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Knowledge Hub: what lab tests measure

Explanations of 55 laboratory tests: what each one measures and why it may be requested. This is general information to help you understand your tests. It is not medical advice, and your doctor will interpret your results.

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A

Adrenocorticotropic Hormone (ACTH)

Adrenocorticotropic hormone (ACTH) is a single chain polypeptide of 39 amino acids with a molecular mass of approximately 4.5 kd. It is produced in the anterior pituitary and serves to stimulate steroid production by the adrenal cortex. ACTH secretion is in turn controlled by the hypothalamic hormone corticotropin releasing factor (CRF) and by negative feedback from cortisol.

ACTH determinations are valuable in the differential diagnosis of adrenal insufficiency and hypersecretion. In Addison’s disease (primary adrenal insufficiency), elevated ACTH levels are typical, whereas low levels are the rule when adrenal insufficiency is secondary to pituitary disfunction. ACTH determinations can also help to Identify the cause of cortisol hypersecretion in Cushing’s syndrome. ACTH levels are typically low when this is due to lesions or hyperplasia of the adrenal cortex, and high when it is due to ectopic ACTH production or hypersecretion of ACTH by the pituitary.

Plasma levels of ACTH exhibit a significant diurnal variation. It is important, therefore, to standardize the time of collection.

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Alpha Fetoprotein (AFP)

Alpha-fetoprotein (AFP) is a single-chain glycoprotein with a molecular mass of approximately 70 kd. It shares considerable sequence homology with albumin, and is produced by the fetus primarily in cells of the yolk sac, gastrointestinal tract and liver. AFP appears as a major serum protein in the fetus, but its concentration decreases rapidly toward birth. The reappearance of elevated AFP concentrations in adult serum has been observed not only during pregnancy, but also in conjunction with several benign and malignant diseases.

Elevated levels of AFP have been noted in patients with nonseminomatous testicular cancer, and other malignancies such as hepatocellular carcinoma, ovarian cancer, gastrointestinal cancer and pulmonary cancer. Serum AFP is frequently elevated in benign hepatic conditions such as acute viral hepatitis, chronic active hepatitis and cirrhosis. Conditions of pregnancy, ataxia telangiectasia and hereditary tyrosinemia have also presented with elevated concentrations of AFP. Seminomas, in pure form, do not present with elevated concentrations of AFP. However, elevated concentrations of serum AFP have been observed in patients diagnosed with seminomatous testicular cancer accompanied by nonseminomatous metastases. During chemotherapy, patients with advanced seminoma and hepatic dysfunction have also presented with elevated serum AFP concentrations. The interpretation of elevated AFP concentrations in patients with seminoma requires special consideration and should assist the clinician in the selection of appropriate therapy. The clinical utility of AFP measurement as an aid in the management of patients with nonseminomatous testicular cancer is well documented. AFP measurement has found clinical application as an aid in assessing the extent of disease.

Serial measurements of serum AFP have been shown to reflect the effectiveness of therapeutic regimens in patients with nonseminomatous testicular tumors. Post-surgical determinations of AFP are particularly valuable. The presence of residual tumor is strongly suggested if post-operative AFP concentrations fail to return to normal. The accurate interpretation of post-surgical changes in AFP concentration requires consideration of its metabolic decay rate. When utilizing AFP for monitoring therapy or disease recurrence during chemotherapy, it should be noted that levels often fall rapidly during chemotherapy, reaching normal levels while tumor masses are still evident. In such instances, completion of the planned therapy has been recommended. Following therapy or surgery, serial measurements of AFP have also been proved clinically useful when monitoring for progression or recurrence of disease in patients with nonseminomatous testicular cancer. It has been reported that AFP levels frequently rise during disease progression and fall during disease remission. Elevated AFP levels have frequently been observed to accompany tumor recurrence before progressive disease is clinically evident.

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α-Androstenedione

α-Androstenedione is a steroid, which serves as a major precursor for testosterone and estrone. Its clinical interest is derived from the fact that it is often elevated in cases of abnormal hair growth (hirsutism) and virilization. Unlike the adrenal androgens, dehydroepiandrosterone and its sulfate, circulating androstenedione originates both from the adrenals and from the ovaries. Plasma levels increase steadily from about the seventh year of life, then gradually decline after the third decade. Androstenedione exhibits a diurnal variation, being highest in the morning, and also a cyclical variation during the menstrual cycle, being highest near midcycle. During pregnancy, there is an increase in the plasma level.

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Anti Double Stranded DNA (Anti-dsDNA)

Antinuclear antibodies (ANA) directed against a variety of macromolecules occur in extraordinarily high frequency in systemic rheumatic diseases. Many rheumatic diseases are characterized by the presence of one or more of these ANA. Therefore, the identification of the specific antibody is useful in the detection and diagnosis of the disease.  Anti-dsDNA is present in 50% to 70% of patients with SLE (systemic lupus erythematosus). Circulating DNA/anti-DNA immune complexes are considered a part in the pathogenesis of SLE. The presence of anti-dsDNA is one of the diagnostic criteria for SLE. IgG antibodies to dsDNA are clinically useful in the diagnosis and management of SLE.  Antibodies to single stranded DNA and IgM antibodies to dsDNA are found in a number of other connective diseases, liver diseases, and in some normal individuals. Accurate detection of anti-dsDNA is important in the diagnosis and management of SLE.

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Anti-Cardiolipin Antibodies

Anti-phospholipid antibodies are autoantibodies that react with most negatively charged phospholipids, including cardiolipin (CL). Additionally, anti-phospholipid antibodies are known to prolong invitro phosphollipid-dependent coagulation tests and have been historically referred to as the “lupus anticoagulant”. Paradoxically, patients with the lupus anticoagulant do not present with abnormal bleeding except in the presence of other hemostatic abnormalities.

Anti-cardiolipin (aCL) antibodies are frequently found in patients with systemic lupus erythematosus (SLE). They are also found in patients with other autoimmune diseases, as well as in some individuals with no apparent previous underlying disease. Elevated levels of aCL antibodies have been reported to be significantly associated with the presence of both venous and arterial thrombosis, thrombocytopenia, and recurrent fetal loss. The term “anti-phospholipid syndrome” (APS) has been introduced to describe patients who present these clinical manifestations, in association with aCL antibodies or the lupus anticoagulant.

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Antinuclear Antibody (ANA) screening

The serological detection of antinuclear antibodies (ANA) in patients with suspected autoimmune disorders is a common practice. Inflammatory connective tissue diseases are characterized by idiopathic genesis along with disturbances in terms of cellular and humoral immunity, systemic organ failure, and a chronic course of disease. Additionally, connective tissue diseases exhibit over-lapping symptomatic features thus making a right diagnosis extremely difficult.  Systemic lupus erythematosus (SLE), Sjogren’s syndrome, progressive systemic scleroderma along with CREST syndrome, Sharp’s syndrome (mixed connective tissue disease) and myositis belong to the inflammatory rheumatic diseases. Considering the diversitivity of mixed connective tissue diseases such disorders exhibit a common serological characteristic: the presence of anti-nuclear antibodies. Those antibodies are directed against parts of the cell nucleus and the cytoplasm. For the most part the presence of a particular ANA in a patient serum can be assigned to a special inflammatory disease.

When an autoimmune disorder is suspected the first diagnostic step is the performance of a screening test on ANA. Common practice is indirect immunofluorescence on HEp-2 cells. The second step in the ANA algorithm is the isolated detection of the particular antibodies specificities. In between an additional screening test can be performed.

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Antistreptolysin-O (ASO)

Autoimmune diseases are illnesses in which the immune system attacks normal components of the body as if they are foreign substances. Rheumatoid arthritis, rheumatic heart disease and lupus erythematosus are autoimmune diseases in which serological testing is important for effective patient treatment and disease management.

Rheumatoid arthritis is an immunologic response of the patient’s immune system to the presence of an immunoglobulin auto-antibody. These “anti-self’ complexes bind with complement, which can eventually lead to the destruction of synovium, cartilage and bone.

Rheumatic heart disease is believed to be a result of childhood infection by group A, beta hemolytic streptococcal bacteria. It sometimes develops following mild, asymptomatic infections. The antibodies formed against the bacteria can cause inflammation of the heart and damage to the heart valves, which eventually could lead to valve malfunction and even death.

Quantitation of rheumatoid factor (RF) is valuable for assessing immunologic response in patients with rheumatoid arthritis and in monitoring the effectiveness of anti-rheumatic therapy. 

Measurement of C-reactive protein (CRP), an acute phase protein, is an additional important index for monitoring rheumatoid-related and other inflammation resulting from autoimmune disease.

The addition of the antistreptolysin 0 (ASO) assay to the serology panel is useful in differentiating inflammation due to rheumatic fever from that associated with rheumatoid arthritis and other autoimmune diseases.

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C

C-Peptide

Human C-peptide is a 31 amino acid chain with a molecular mass of approximately 3,020 daltons. Metabolically inert, it originates in the pancreatic β-cells as a by-product of the enzymatic cleavage of proinsulin to insulin. In this process, insulin and C-peptide are split from the prohormone and secreted into the portal circulation in equimolar concentrations. It is this fact which underlies the clinical interest in plasma determinations of C-peptide.

Within limits, C-peptide levels can serve as a valuable index to insulin secretion. Thus, low C-peptide levels are to be expected where insulin secretion is diminished, as in insulin-dependent diabetes, or suppressed, as a normal response to exogenous insulin; whereas elevated C-peptide levels may result from the increased β-cell activity observed in insulinomas.  Accordingly, in the differential diagnosis of hypoglycemia, C-peptide determinations can be used to supplement insulin measurements as an index to pancreatic activity in the classic 72-hour fasting test, and as the sole indicator of pancreatic activity where insulin itself is administered to check for suppressibility. In addition, covert self-administration of insulin can be virtually ruled out as the cause of hyperinsulinemia by the finding of an elevated C-peptide level.

Circulating anti-insulin antibodies are commonly encountered in patients who have undergone insulin therapy. These would typically interfere with immunoassays for insulin, making it impossible to use insulin measurements in this context to check on residual β-cell activity, even if treatment were temporarily suspended.  C-peptide measurements have therefore been used as an alternative in this context, to yield information on the natural history of insulin-dependent diabetes, to indirectly monitor insulin secretion in the presence of anti-insulin antibodies, and to help settle on an appropriate course of treatment.

C-peptide has also been measured as an additional means for evaluating glucose tolerance and glibenclamide-glucose  tests.

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C-Reactive Protein (CRP)

CRP is an acute phase β-globulin with a molecular mass of approximately 118,000 daltons. CRP is highly conserved, composed of five identical cyclic globular subunits, and is classified as a member of the pentraxin superfamily of proteins. CRP levels in serum or plasma may rise during general, nonspecific response to infectious and non-nfectious inflammatory conditions such as rheumatoid arthritis, cardiovascular disease and peripheral vascular disease. CRP is synthesized in the liver and is normally present as a trace constituent of serum or plasma.  While the precise in vivo functions of CRP during the inflammation state are not known, there is considerable evidence indicating a role in the recognition and elimination of foreign pathogens, as well as potentially toxic endogenous substances released from damaged tissue, by assisting humoral and cellular immunity. In normal individuals, hepatic cells produce CRP at constitutive levels of less than 1 mg/dL.  Within 24 to 48 hours following acute tissue damage, production dramatically rises to approximately 1000 times the constitutive level. CRP levels may remain elevated for several days before returning to normal.

As elevated CRP values are always associated with pathological changes, the CRP assay provides useful information for the diagnosis, therapy, and monitoring of inflammatory conditions and associated diseases. Additionally, measurement of CRP by high sensitivity CRP assays may add to the predictive value of other markers used to assess the risk of cardiovascular and peripheral vascular diseases.

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Cancer Antigen 125 (CA125)

CA 125 is identified as a 200 to 1000 kDa mucin-like glycoprotein. CA 125 is a surface antigen associated with nonmucinous epithelial ovarian cancer. The protein is sloughed or secreted from the surface of the ovarian cencer cells into the serum or ascites. The antigen reacts to a murine monoclonal antibody, OC 125, that was originally developed by immunizing mice with cells from ovarian cancer cell line OVCA 433. Second-generation assays for CA 125 utilize both the OC 125 and M 11 epitopes yielding an improved assay range.

CA 125 is a useful tumor marker for evaluating therapy and monitoring disease status in patients under treatment for ovarian cancer. Post-operatively, the level of CA 125 correlates with tumor bulk and is a prognostic indicetor of clinical outcome. It has been reported that patients with levels exceeding 35 U/mL have the highest risk for clinical recurrence.

It has been reported that prior to a second-look laparotomy, a patient with levels of CA 125 greater than 35 UlmL is very likely to have tumor present at the surgery or to have a future recurrence. However, a level of CA 125 less than 35 U/mL prior to a second-look operation is not definitive evidence that the patient is free from residual tumor. Levels of CA 125 measured after a second-look operation provide strong indications of clinicel outcome. Measured serially, the levels of CA 125 correspond with disease progression or regression. The rate of change in CA 125 is also highly prognostic. A rapid decrease in the level of CA 125 indicates a positive response to treatment. Elevated levels of CA 125 after the third course of primary chemotherapy are predictive of pool outcome. 

As a diagnostic tool, the level of CA 125 alone is not sufficient to determine the presence or extent of disease. Preoperative levels of CA 125 in patients with malignant pelvic masses provides no information regarding the histologic grade or diameter of the tumor mass. In postmenopausai women, however, the level of CA 125 in combination with ultrasonography may distinguish benign from malignant pelvic masses. Patients with certain benign conditions, such as hepatic cirrhosis, acute pancreatitis, endometriosis, pelvic inflammatory disease, menstruation, and first trimester pregnancy, have shown elevated levels of CA 125. Elevated levels are found in 1 to 2% of healthy donors.

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Cancer Antigen 15-3 (CA 15-3)

CA 15-3 is a highly polymorphic glycoprotein belonging to the mucin family and is the product of the MUC-1 gene. Metastatic breast cancer is usually associated with circulating cancer-related antigens such as CA 15-3. In industrialized nations one in ten women can expect to be diagnosed with breast cancer at some point in her lifetime. The vast majority of breast cancer deaths are from advanced, disseminated disease. Although many therapeutic modalities exist for the treatment of metastatic disease, most breast cancers usually become refractory to specific drugs and require second and third line regimens. A circulating tumor marker, such as CA 15-3, which can monitor response to therapy and can indicate disease status is a valuable tool in the management of these patients. It Is most useful using serial measurements to monitor both the course of disease and response to therapy because of the direct correlation of changing levels of CA 15-3 with clinical status. In patients with known metastases, a reduction in levels of this marker indicates a good response to treatment while increasing levels indicate resistance to therapy and progressive disease and justify further clinical evaluation and regular monitoring. It has also recently been shown that an elevation of CA 15-3 levels above the upper limit of normal in patients with no clinical evidence of disease is an early indicator of recurrence. An elevated serum CA 15-3 level in patients in remission of Stage II or III breast cancer provided a positive predictive value of 83.3% for recurrent disease, with an average lead time of 5.3 months before recurrence was clinically established.

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Carbamazepine

Carbamazepine is an iminostilbene derivative used for the treatment of epilepsy; trigeminal neuralgia; and simple and complex, partial and generalized convulsive seizures. It is administered either alone or in combination with other antiepileptic drugs.  Carbamazepine is rapidly absorbed into the bloodstream, where it binds with protein (60 to 80 percent). The drug is metabolized by hepatic oxidation to the 10, 11-epoxide form, which is as active as the parent drug. The epoxide form is further metabolized to the 10, 11-dihrdroxide, which is eliminated in the urine. The presence of other drugs can significantly alter the rate of epoxide formation: phenytoin, phenobarbitol and felbamate induce the metabolic enzyme activity, whereas erythromycin and propoxyphene inhibit this activity.

The therapeutic range for carbamazepine is between 4 and 12 μg/ml with toxic levels above 15 μg/ml. However, individual differences in absorption and metabolism can result in highly variable responses to carbamazepine. Monitoring levels assists the physician in optimizing dosage and minimizing toxic side effects for each patient.

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Carcinoembryonic Antigen (CEA)

Carcinoembryonic antigen is a glycoprotein nonmally found in embryonic entodermal epithelium. In  the mid 1960s, Gold and Freedman isolated CEA from extracts of malignant tissue.  CEA belongs to a group of tumor markers referred to as oncofetal proteins. Increased serum CEA levels have been detected in persons with primary colorectal cancer and in patients with other malignancies including gastrointestinal tract, breast, lung, ovarian, prostatic, liver, and pancreatic cancers. Elevated serum CEA levels have also been detected in patients with nonmaiignant disease, especially patients who are older or who are smokers. CEA levels are not useful in screening the general population for undetected cancers. However, CEA levels provide important information about patient prognosis, recurrence of tumors after surgical removal, and effectiveness of therapy.

Serial CEA levels are useful in monitoring the course of disease. CEA levels generally fall to normal or near normal levels within 1 to 4 months after surgical removal of cancerous tissue. A rise in CEA levels may be the first indication of recurrence, and may precede physical signs and symptoms. Serial CEA levels are also useful in assessing the effectiveness of chemotherapy or radiation treatment. A sustained rise in CEA levels can indicate ineffective therapy or possible metastasis. CEA is a useful tool for monitoring and managing cancer therapy, and provides the clinician with additional information about patient prognosis.

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Chlamydia (CHL)

Chlamydia are nonmotile, gram-negative, obligate intracellular bacteria They rely on host cell ATP for replication, forming characteristic intracellular inclusions which can be seen by light microscopy. C trachomatis is responsible for a significant portion of sexually transmitted diseases seen in the world. Chlamydial infection in women is often only mildly symptomatic or asymptomatic. Pregnant women infected with C trachomatis can pass the organism on during birth, causing conjunctivitis or pneumonia in the newborn chronic salpingitis, seen with some cases of chlamydial infection, can cause damage to the fallopian tubes. This can lead to ectopic pregnancy or infertility In males, C trachomatis is a major cause of nongonococcal urethritis (NGU). Diagnosis is based on symptomatic presentation or history of contact with an infected person. This is then confirmed by cell culture. Cell culture techniques have improved over the years, but are labor-intensive and require at least 48 hours to obtain results and necessitate Giemsa, Iodine or fluorescent antibody staining for confirmation. Although culture is still considered to be the gold standard for diagnosis of chlamydial infection, antigen detection techniques are easier to perform and are used in an increasing number of clinical labs. Direct detection methods currently in use are direct immunofluorescence microscopy, enzyme immunoassay, and nucleic acid assays.

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Cortisol

Cortisol (hydrocortisone, Compound F) is the most abundant circulating steroid and the major glucocorticoid secreted by the adrenal cortex. Physiologically effective in anti-inflammatory activity and blood pressure maintenance, cortisol is also involved in gluconeogenesis, calcium absorption and the secretion of gastric acid and pepsin.

As an indicator of adrenocortical function, measurement of blood cortisol levels is useful in the differential diagnosis of Addison’s and Cushing’s disease, hypopituitarism, and adrenal hyperplasia and carcinoma. A variety of stimulation and suppression tests – ACTH stimulation, ACTH reserve, Dexamethasone suppresion can supply supportive information on adrenocorticol function.

Anomalous cortisol concentrations have been shown to exist in patients with acute infections, severe pain, diabetes mellitus or heart failure, and in women either pregnant or on estrogen therapy. In addition, certain virilizing syndromes and iatrogenic conditions raise other naturally occurring steroid levels to high (nonphysiologic) concentrations that may interfere with assaying cortisol directly, unless a highly specific antiserum is used.

Because of diurnal rhythms, determinations of serum cortisol levels in the morning as well as evening are routinely advocated. But serum cortisol levels vary widely in normal individuals from ~5-30 μg/dl at 8.00 AM and is generally reduced by 50% at midnight. Evaluation of 24 hour urinary free cortisol excretion is therefore considered the most useful reflector of overall adrenocortical function. Typically, the normal basal excretion of cortisol is <100 μg/24 hour. Values consistently >250 μg/24 hour are virtually diagnostic of Cushing,s syndrome. However, it is of importance to note that because of the profound effects of abnormal thyroid function on urinary steroid excretion, it is essential that thyroid status be evaluated first and the patient be euthyroid at the time of adrenal evaluation.

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Cytomegalovirus Antibodies

Cytomegalovirus (CMV), a member of the herpes virus family, is found throughout the world. Humans of all ages are susceptible and infection is spread through sexual contact, direct exposure to infected body fluids, blood transfusions and organ transplants. The majority of infections are asymptomatic however, CMV infections can be severe in neonates and immunocompromised individuals. Infection can also be severe in patients with congenital or acquired cellular immune defects, including cancer patients, organ recipients and AIDS patients.

CMV is the most common congenital infection, infecting between 0.5 and 2.5 percent of newborn infants. Five percent of these will develop classic cytomegalic inclusion disease with jaundice, pneumonia and central nervous system disorder. Infected infants may be asymptomatic at birth, but can develop neurological problems later in life. Between 40 and 100 percent of people, have detectable antibody, with the prevalence highest in developing countries.

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D

Dehydroepiandrosterone Sulphate (DHEA-S)

Measurement of dehydroepiandrosterone sulfate (DHEAS), an adrenal steroid, is important to investigations of abnormal hair growth [hirsutism; and balding (alopecia)] in women. It is also of value in the assessment of adrenarche and delayed puberty. DHEA-S in circulation originates almost entirely from the adrenals, though in men some may also be derived from the testes, partly accounting for the sex difference which emerges at about age 15. On the other hand, this hormone is not produced by the ovaries even under pathological conditions. In itself, DHEA-S is only weakly androgenic, but it can be metabolized to more potent androgens like androstenedione and testosterone, and thus be indirectly a cause of hirsutism or virilization.

Plasma levels of DHEA-S increase steadily from about the seventh year of life, then gradually decline after the third decade. Pregnancy and oral contraceptives induce a moderate decrease. Unlike cortisol, DHEA-S04 does not exhibit significant diurnal variation. Unlike testosterone, it does not circulate bound to sex hormone-binding globulin and hence is not influenced by alterations in the level of this carrier protein. Its abundance, together with its within-day and day-to-day stability, makes it an excellent direct indicator of adrenal androgen output – superior,  certainly, to the measurement of urinary 17 -ketosteroids in this context. Accordingly, DHEA-S is often assayed in conjunction with free testosterone as an initial screen for hyperandrogenism in hirsutism. At least one of these two hormones is likely to be elevated in the great majority of cases – reportedly over 80 percent of the time. Sometimes DHEA-S is the only hormone circulating at a level above normal, and is apparently more likely to be elevated during the early stages of hirsutism than most other androgens.

High DHEA-S levels are often encountered in the polycystic ovary syndrome, showing that adrenal hyperandrogenism is a fairly typical facet of this syndrome. Elevated plasma levels which – over the course of two weeks or so – are dexamethasone-suppressible may also result from adrenal  hyperplasia. Extremely high levels of DHEA-S are suggestive of a hormone-secreting adrenal tumor. By contrast, DHEA-S levels are typically normal in the presence of ovarian tumors.

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Digoxin

Digoxin belongs to the class of compounds known as digitalis glycosides, and is the most commonly prescribed drug for congestive heart failure (CHF). Digoxin strengthens the contraction of the cardiac muscle and reduces heart rate by improving cardiac output. In addition, digoxin therapy is also indicated in most cases of atrial fibrillation and atriail flutter whether or not CHF is present.

Therapeutically, digoxin is effective within a narrow serum concentration range. Knowledge of the serum level is important for establishing optimal doses for the patient and for diagnosing digoxin toxicity. Toxic levels can be reached from repeated doses when renal function is impaired because 60 to 90% of digoxin is excreted in the urine unchanged. Other complications that add to digoxin toxicity include: variation in gastrointestinal absorption & variation in nonrenal excretion.

Varation in gastrointestinal absorption.

Variation in non-renal excretion

an inaccurate history of dosage

(Digoxin toxicity is a frequent complication of digoxin therapy. In patients with CHF, symptoms of digoxin toxicity frequently resemble symptoms of CHF itself. In other words, high toxic levels of digoxin often mimic sub-therapeutic levels, thereby complicating therapy.

Some patients require or tolerate doses that are highly toxic for other patients. Patients exhibiting toxic effects are frequently elderly individuals and those with impaired renal function. Therefore, each serum level must be interpreted with the patient’s clinical status in mind.

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E

17 β-Estradiol (E2)

Estradiol is a steroid hormone with a molecular mass of 272.3 daltons which circulates predominantly protein-bound. In addition to estradiol, other natural steroidal estrogens include estrone, estriol and their conjugates. Estrogens are hormones secreted principally by the ovarian follicles and also by the adrenals, corpus luteum, placenta and, in males, by the testes.

Estrogenic hormones are secreted at varying rates during the menstrual cycle throughout the period of ovarian activity. In assisted reproductive techniques, circulating E2 concentrations are helpful in monitoring follicular maturation under gonadotropin stimulation.

The gonadotropins of the anterior pituitary regulate secretion of the ovarian hormones, estradiol and progesterone; hypothalamic control of pituitary gonadotropin production is in turn regulated by plasma concentrations of the estrogens and progesterone. This complex feedback system results in the cyclic phenomenon of ovulation and menstruation.

During pregnancy, the placenta becomes the main source of estrogens. At the menopause, ovarian secretion of estrogens declines at varying rates.

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F

Ferritin

The ferritin molecule consists of a protein shell (MW 450,000) and a core of iron. High concentrations are found in liver cells and in erythrocyte recycling centers (RE cells) of the liver, spleen and bone marrow. In these tissues, ferritin serves as the body’s principal storehouse for surplus iron, protecting against the toxic effects of excess and maintaining a readily mobilized reserve for erythropoiesis. Ferritin is also present in human plasma, where its concentration is normally a satisfactory index of body iron stores.This relationship with iron stores can be seen in the pattern of serum ferritin values under a variety of physiological and pathological conditions. For individuals in good health the median level, slightly elevated at birth, reaches a low of about 30 ng/mL at six months, with the increase to adult levels taking place after puberty. In males, the median level continues to climb – from about 70 ng/mL at age eighteen to almost 200 ng/mL twenty-five years later – whereas in females there is a plateau at 35 or 40 ng/mL throughout the childbearing years and a sharp increase thereafter. For adults in good health, the serum ferritin level has been variously reported to range from 20 (+10) up to 300 (+100) ng/mL for men, and 10 (+5) up to 150 (+ 50) ng/mL for women. Concentrations below 10 or 15 ng/mL are typical of uncomplicated iron deficiency anemia. For iron overload, values over 300 or 400 ng/mL are the rule, with levels in the 1,000 – 5,000 ng/mL range common in full blown cases of hemochromatosis.

Clinical applications of the serum ferritin assay have been extensively reviewed. It has important roles to play in the diagnosis of iron deficiency and excess, and in the management of conditions and treatments posing a threat to iron balance. It has been  proved as a valuable aid in discriminating iron deficiency anemia from anemias due to other causes and in exposing the disappearance of iron reserves before the onset of anemia.

Serial determinations have been employed to monitor, noninvasively, the progressive erosion of iron stores during pregnancy and in patients undergoing regular dialysis treatment. Both in company with other routine blood tests & and on its own, the ferritin assay has been used to screen for iron deficiency in a variety of populations, ranging from blood donors to unselected hospital patients. It is also valuable in screening for precirrhotic hemochromatosis and other forms of iron overload and in monitoring patients who are receiving regular blood transfusions or iron replacement therapy and thus in danger of accumulating excessive iron stores.

Although iron depletion appears to be the only condition associated with reductions in the serum ferritin level, increases are observed not only in the presence of increased iron stores but also in several other situations, including liver disorders, inflammatory conditions, leukemia, Hodgkin’s disease and certain other malignancies. Here, increased levels may reflect the escape of ferritin from damaged, liver cells, impaired clearance of ferritin from the plasma, synthesis of ferritin by tumor cells, or an expansion of the iron storage compartment induced by ineffective erythropoiesis. Inflammation tends to raise the ferritin level while lowering the serum iron concentration by stimulating increased ferritin production in RE cells, using iron that would otherwise be released to plasma transport proteins. In this condition and others, the correlation between iron stores and circulating ferritin continues to hold, but with a shift towards higher values – necessitating an adjustment in the reference range if the ferritin assay is still to be used for distinguishing normal from depleted iron reserves.

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Folate

Folates are compounds of pteroylglutamic acid (PGA) that function as coenzymes in metabolic reactions involving the transfer of single-carbon units from a donor to a recipient compound. Folate, with vitamin B12, is essential for DNA synthesis, which is required for normal red blood cell maturation. Humans obtain folate from dietary sources including fruits, green and leafy vegetables, yeast, and organ meats. Folate is absorbed through the small intestine and stored in the liver.

Low folate intake, malabsorption as a result of gastrointestinal diseases, pregnancy, and drugs such as phenytoin are causes of folate deficiency. Folate deficiency is also associated with chronic alcoholism. Folate and vitamin B12 deficiency impair DNA synthesis, causing macrocytic anemias. These anemias are characterized by abnormal maturation of red blood cell precursors in the bone marrow, the presence of megaloblasts, and decreased red blood cell survival.

Since both folate and vitamin B12 deficiency can cause macrocytic anemia, appropriate treatment depends on the differential diagnosis of the deficiency. Serum folate measurement provides an early index of folate status. However, folate is much more concentrated in red blood cells than in serum so the red blood cell folate measurement more closely reflects tissue stores. Red blood cell folate concentration is considered the most reliable Indicator  foIate stalus.

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Follicle Stimulating Hormone (FSH)

Follicle stimulating hormone (follitropin, FSH) is secreted by the antirior pituitary under the control of the gonadotropin releasing hormone produced in hypothalamus. FSH facilitates the development and maintenance of gonadal tissues, which synthesize and secrete steroid hormones. Circulating levels of FSH are controlled by a negative feedback mechanism on the hypothalamus by steroidal hormones. Although FSH and LH required for normal sexual function in both males and females, the secretory patterns are very different for the two sexes.

In mature females, FSH initiates the growth and development of ovarian follicles. During ovulation, when the follicle is raptured, the follicle, now called the corpus luteum, secretes estradiol and progesterone, which control the circulating levels of FSH by a negative feedback effect on the hypothalamus. In menopause, with diminished ovarian function, there is a resulting decrease in estradiol secretion. Due to the lack of a negative feedback effect, with diminished estradiol, the circulating FSH levels become significantly increased. In association with amenorrhoea, elevated levels of FSH on 2 or more occasions are considered presumptive evidence of premature ovarian failure.

In the mature male, FSH is associated with the stimulation and maintenance of spermatogenesis. Testosterone and eastradiol have the role of providing the negative feedback signal to the hypothalamus for controlling the release of FSH. Infertility in males may be due to hypogonadism as a result of primary, testicular failure. Testicular failure may be functional failure to mature, or a result of germ cell damage. Whatever the etiology, the conditions of hypogonadism have the net result of dramatically raising the circulating FSH levels, due to the lack of a negative feedback effect.

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G

Growth Hormone / Human Growth Hormone (GH/HGH)

Human growth hormone (hGH, somatotropin) is a 191 amino acid polypeptide chain having a molecular mass of ~ 22 kd originating in the anterior pituitary. Its metabolic effects are primarily anabolic. It promotes protein conservation and engages a wide range of mechanisms for protein synthesis. It also enhances glucose transport and facilitates the buildup of glycogen stores. Another family of peptide hormones, the somatomedins, mediates its cascade of growth-promoting actions.

Measurement of hGH is primarily of interest in the diagnosis and treatment of various forms of inappropriate growth hormone secretion. Clinical disorders of hyposecretion include dwarfism and unattained growth potential. Hypersecretion is associated with gigantism and acromegaly.

Caution must be exercised in the clinical interpretation of growth hormone levels. These vary throughout the day, making it difficult to define a reference range or to judge an individual’s status based on single determinations. Many factors are known to influence the rate of growth hormone secretion, including periods of sleep and wakefulness, exercise, stress, hypoglycemia, estrogens, corticosteroids, L-dopa, and others. Because of its similarity to prolactin and placental lactogen, earlier growth hormone immunoassays were often plagued with falsely high values in pregnant and lactating women. Because not all acromegalic individuals have elevated baseline levels, suppression tests based on glucose loading are of value in this context. In spite of the induced hyperglycemia, there is rarely a decrease from baseline levels in acromegaly.

Growth hormone-deficient individuals have fasting/resting levels similar to those found in healthy individuals. Various challenge tests have therefore been devised to differentiate these groups. Thus, with the onset of deep sleep or after 15 to 20 minutes of vigorous exercise, growth hormone levels normally show a rise. Other tests of growth hormone responsiveness are based on the administration of L-dopa, arginine and insulin. Propanolol or estrogen are sometimes given in conjunction with the primary stimulus to accentuate the response.

A small number of cases of dwarfism have been documented in which both the basal level and the response to challenge testing were normal. Such cases may involve tissue insensitivity to either growth hormone or the somatomedins, or the presence of antibodies or immunoreactive but biologically inactive growth hormone.

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H

Hepatitis B core Antibody, IgM (HBc IgM)

The hepatitis B virus causes acute, and occasionally fulminant viral hepatitis, but also chronic hepatitis which may result in cirrhosis and cancer of the liver, proving fatal for over 2 million carriers every year. In a study completed in 1990 , more than 2000 million people worldwide have been infected, including approximately 280 million chronic carriers. Acute hepatits B virus carriers are usualiy asymptomatic. Infection will lead to jaundice in approximate 10 % of infected subjects. One percent of icteric patients will develop fulminant hepatitis, which has an 80 % mortality rate . Chronic infection may lead to cirrhosis in 15 to 30 % of patients, which can be further complicated by hepatocellular carcinoma in 30 to 40 % of patients.

The normal course of chronic infection comprises three phases :

– an active replication phase, which can last for several years, during which viral replication is high, but the destruction of hepatocytes is moderate,

– an inactivation phase, during which viral replication is slow, but the destruction of hepatocytes increases, due to the HBc antigen present on the cell surface, and the strong immune response,

– an inactive phase, during which HBc Ag is no longer synthesized and viral replication no longer occurs. One or several phases of reactivation are possible.

The hepatitis B virus has a very limited cytopathogenic effect. Hepatocellular necrosis is caused by the immunocellular response to HBc Ag on the surface of the hepatocytes.

Diagnosis of hepatitis B relies on the detection of HBs surface antigen and IgM anti-HBc. The level of infectivity, and infection evolution will be assessed by other markers; they will also enable a discrimination between patients that need to be screened. The HBs antigen will either disappear in case of a positive evolution after 2 or 6 months or remain in chronic carriers.

In the case of fulminant hepatitis, HBs antigen can disappear at an early stage. Determination of anti-HBcIgM is then the only indication of HBV infection. The ultra sensitive quantitative tests enable patients to be monitored from the time HBs Ag appear up to the appearance of anti-HBs Ab, by titering the anti-HBc IgM, and also a distinction to be made between healthy carriers and those with active chronic hepatitis. In cases of chronic hepatitis, anti-HBc IgM is a very sensitive indirect marker of viral replication, but also of the host response to HBc Ag in the liver. As with serum HBe Ag and HBV DNA, a positive result for anti-HBc IgM is of considerable assistance in the diagnosis of chronic hepatitis, but a negative result does not necessarily exclude this possibility. The diagnosis should therefore be made using both histological and serological criteria. In patients with a significant response, titration of anti-HBc IgM enables anti-viral treatments to be monitored by a specific marker of HBV.

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Hepatitis B envelope antibody (Anti-Hbe)

The C gene of the HBV viral genome can express two distinct proteins 1) core protein (HBc Ag) which forms the nucleocapsid 2 e non-particulate protein (HBe Ag). HBe Ag can be detected in the serum of patients  with hepatitis B wild-type virus during active viral replication . The function of this antigen in the viral replication cycle is not clearly defined. It is not indispensable to the virus, however this antigen is a major immunological target in the clearance of the virus. Generally, HBe Ag can be detected early in an acute HBV infection.It coincides with or follows the appearance of HBs Ag. In acute cases which evolve to recovery, HBe Ag disappears after several weeks and seroconversion to anti-HBe usually follows. For chronic HBV cases, HBe Ag can persist from several months to as long as several years, indicating on-going viral replication. The presence of HBe Ag in serum indicates active replication of HBV and people with HBe Ag- positive results are considered highly infectious for hepatitis B.

HBe Ag is used to monitor chronic hepatitis and anti- viral therapy. The objective of anti-viral therapy is to prevent the progression to liver cirrhosis. HBe Ag seroconversion to anti-Hbe  is generally considered as an indicator of transition to a state of viral latency accompanied by normalization of aminotransferase levels. HBe Ag seroconversion to Anti-HBe reduces the risk of developing cirrhosis and decompensated liver disease .

A positive result for anti-HBe in patients recovering from acute hepatitis indicates normal recovery, particularly if HBsAg and HBe Ag are no longer detectable. In an HBV carrier, a positive anti-HBeV result usually indicates inactivity of the virus and low infectivity of the patient. However a positive anti-HBe result in the presence of a positive HBV-DNA test result, as found in HBV mutants, can indicate active viral replication and progression of liver disease in a carrier. HBV mutants unable to secrete HBe Ag, can prevail over wild-type HBVs in patients with severe acute and chronic hepatitis B and in chronic HBs Ag carriers at the time of HBe Ag/anti-HBe seroconversion. These mutants are positively selected by the anti-viral immunoreaction.

Because this mutation affects only a portion of the viral population, serum HBe Ag and anti-HBe antibodies can be simultaneously detected during a period which varies depending on the individual.

Perinatal transmission of hepatitis B virus is frequent in areas with a high endemicity of the infection or in countries where screening of pregnant women is not undertaken regularly. About 90% of HBe Ag positive mothers transmit HBV to their infants and 90% become chronic HBs Ag carriers.

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Hepatitis B Surface antibody, Total (HBST)

85 % of patients infected with the hepatitis B virus evolve towards recovery (appearance of anti-HBs Ab, considered to be immunity markers) and the remaining 15 % become chronic carriers. In areas where hepatitis B is endemic, all individuals are at risk. Elsewhere, indviduals with multiple sexual partners, drug-abusers, medical workers, immunosuppressed patients, and children with HBs antigen positive mothers are concerned. Vaccination strategies against the hepatitis B virus depend on the epidemiologic: situation Vaccination is highly recommended for patients at risk.

In cases of acquired immunity following infection by the hepatitis B virus, presence of anti-HBs antibodies is associated with anti-HBc antibodies.

Patients vaccinated against HBV will only be anti-HBs positwe. Post-vaccine protection is limited to a period of time, which is directly related to the concentration of anti- HBs currently admitted of at least 10 mIU/ml. Regular controls are essential to determine the need for booster injections.

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Hepatitis B Surface Antigen (HBsAg), Australia Antigen

Hepatitis-B virus (HBV) is the sole human pathogen in the family of hepatitis-associated DNA viruses, and is found world-wide. Distribution of HBV infection will vary among geographical areas and population groups. Transmission of the virus is due to parenteral contact, through the exchange of blood or blood products, sexual contact, and perinatal spread from mother to newborn. Clinical manifestations range from mild asymptomatic infections to severe fulminant hepatitis. Over 90% of infected adults will have an acute self- limiting infection, with jaundice and abnormal liver function. Recovery occurs without any chronic sequelae. Chronic liver disease, a condition in which infection persists for more than six months, a known sequel of a hepatitis-B infection, is usually progressive. The risk of developing the chronic carrier state is more likely to follow infection acquired in childhood than as an adult. In chronic HBV carriers, there is no evidence of continued hepatic damage, however, the infection persists and the carrier maintains the ability to transmit the virus.

Availability of recombinant HBV vaccines, and the recommendation of universal immunization for infants and other high-risk persons has aided in the prevention of HBV infections. In addition, treatment with alpha-interferon to relieve symptoms is available. Results have shown positive response to treatment in 40-50% of selected individuals with chronic active hepatitis-B.

Classification of a hepatitis B infection requires the identification of several serological markers expressed during three phases (incubation, acute and convalescent) of the infection. The first marker to appear in serum is hepatitis B surface antigen (HBsAg). Presence of this antigen indicates an ongoing infection with HBV and is detectable in the acutely ill and in chronic carriers.

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Hepatitis E virus Antibodies (HEV)

Hepatitis E Virus (HEV) is a recently discovered agent of enterically transmitted non-A, non-B hepatitis. The HEV infection has a worldwide distribution and a predominat waterborn route of transmission. The first reported outbreak of this infection occured in New Delhi; since this time, epidemics on hepatitis E have been documented in many countries. HEV shows morphological and biophysical properties similar to viruses found in the family Caliviridae. The HEV genom consists of a single stranded RNA molecule that contains 3 open reading frames (ORF1, ORF2, ORF3) That encode for non-structural and structural proteins.

Epitope mapping of the viral genome have lead to identify the presence of highly immunoreactive type common epitopes. Synthetic peptides or recombinant expressed proteins, derived from these regions, have been used to develop enzyme immunoassay for the detection of IgG and IgM antibody. Antibody to HEV of IgM class appears associated to acute stage of infection, while antibody to IgG class characterizes previous HEV exposure.

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Herpes Simplex virus 1 & 2 Antibodies (HSV 1&2)

Herpes simplex virus (HSV) is an ancient and ubiquitous virus, known to cause acute and recurrent infections in humans. The virus enters the mucous membranes (ocular, genital or oral) and replicates locally. Infection of neonates during passage through the birth canal may result in neurological damage and death. In a small portion of infected individuals, the virus may enter the sensory root ganglion, resulting in latent, recurrent infections.

In the 1960s it was recognized that HSV consisted of two distinct types, HSV-I and HSV-II. HSV-I is considered to be primarily associated with ocular and oral infection, while HSV-II is considered to be a genital infection. Clinical cases primarily are 1) Eczema herpeticum, with eczematous skin changes with numerous lesions, 2) Gingivo-stomatitis and 3) Herpes sepsis, almost only found in newly born of premature infants. However, HSV types I and II share several common antigens, and the use of specific monoclonal antibodies or restriction endonuclease mapping may be required to type individual strains.

Infections with HSV type I or type II can differ in their clinical manifestations and severity. The immune response of the host can play an important role in controlling the severity of primary or reactivated infections. Those at highest risk are neonates, who contact the infection during passage through the birth canal, and immunocompromised patients.

While isolation of the virus in tissue culture is recommended for the diagnosis of active infections, serological testing can provide valuable information in the management of at-risk populations, such as pregnant women,

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Homocysteine

Total (tHcy) has emerged as an important risk factor in the assessment of cardiovascular disease.3-7,12 Hcy, a thiol-containing amino acid, is produced by the intracellular demethylation of methionine. Hcy thereby serves as a pool that can be later scavenged for use in the remanufacture of either methionine through the action of the folate-dependent enzyme methionine synthase or cysteine using the B6 dependent transsulphuration pathway. 1,2Hcy in plasma is found primarily in a protein bound form but free, oxidized and disulfide forms are also present. Highly elevated levels of tHcy are found in patients with homocystinuria, a rare genetic disorder of the enzymes involved in Hcy metabolism 1,2,3 Homocystinuria patients exhibit arterial thromboembolism, mental retardation and early arteriosclerosis.1 Less severe genetic defects are also associated with moderate levels of Hcy.

Homocysteine has been identified as a indicator of cardiovascular disease. A meta-analysis of 27 epidemiological studies has suggested that a 5 µmol/L increase in tHcy could be associated with an odds ratio for coronary artery disease (CAD) of 1.6 for men and 1.8 for women, the same increase in risk as a 0.5 mmol/L increase in cholesterol.7 In addition, patients with chronic renal disease complicated by arteriosclerotic cardiovascular disease show elevated tHcy due to the inability of the kidney to remove Hcy from the blood.

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Human Chorionic Gonadotropin (HCG), Total

Human chorionic gonadotropin (HCG) is a two-chain glycoprotein hormone (MW -37,000) normally found in blood and urine only during pregnancy. It is secreted by placental tissue, beginning with the primitive trophoblast, almost before and / or from the time of implantation, and serves to support the corpus luteum during the early weeks of pregnancy. Circulating – HCG typically reaches levels of approximately 2,000 mIU/mL one month after conception. A peak level on the order of 100,000 mIU/mL is attained in the third month, after which a gradual decline sets in. Following delivery, the HCG level normally undergoes rapid descent, reaching nonpregnant concentrations (usually less than 5 mIU/mL) some two weeks later. Ectopic pregnancies and pregnancies terminating in spontaneous abortion tend to have lower than normal circulating HCG levels, while somewhat higher levels are often seen in multiple pregnancies. Many publications describe the value of detecting multiple HCG-related molecules in abnormal pregnancies, aneuploidy (trisomy-21 pregnancies), spontaneous and threatened abortions, preeclampsia, cancers and trophoblastic diseases.

Choriocarcinomas, one of the gestational trophoblastic diseases, arise mostly in the uterus from hydatidiform mole, following abortion, or during normal pregnancy. They can also occur in the testis. Although choriocarcinomas represent less than 1 percent of gynecological malignancies, they are important to recognize: early treatment of this life- threatening cancer results in a high cure rate. Metastases are commonly found at diagnosis and are taken into account in disease staging. HCG and especially the free-β-HCG subunit can aid in the diagnosis and monitoring of choriocarcinomas.

In testicular tumors, measurement of HCG in conjunction with α-fetoprotein  is used as an aid in determining tumor type (seminoma, nonseminoma), prognosis and therapy. These tumor markers are essential monitoring tools; failure of either marker to return to normal after therapy indicates residual tumor. In certain testicular tumors, the ratio of free-β-HCG subunit to HCG can be quite high; occasional tumors secrete only the free-β subunit and virtually no detectable intact HCG.

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Human Immunodeficiency virus (HIV)

Human immunodeficiency viruses (HIV) are RNA retroviruses transmitted via sexual contact, parenteral and perinatal pathways or the placenta. HIV1 and HIV2 were respectively isolated in 1983 and 1985 in patients infected by AIDS (Acquired Immunodeficiency Syndrome). Since then numerous genetic variants have  been characterized. These mutations seemed to be  without consequence for serological diagnosis until HIV1 variants of group O (Outlier) were isolated, since they have only 50 % homology at the env gene level with  those of group M (Major)

During 1995, 2.7 million adults were newly infected by HIV and 500,000 children were born infected with HIV. From the beginning of the pandemic until the middle of 1996, an estimated 27.9 million people were infected by the HIV virus. This figure includes 7.6 million people who contracted AIDS.

Current diagnosis of HIV infection relies on the detection of anti-HIV serum antibodies using an ELISA method. : However, there is a mean period of 3 weeks between contamination and the appearance of the first antibodies. Recent studies have shown that during this period p24 antigen was present in most people infected by , HIV1, regardless of their origin. Thus simultaneous detection of p24 antigenemia, anti-HIV1 and anti-HIV2  antibodies enables the time lapse between contamination and diagnosis of the infection to be decreased.

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I

Immunoglobulin E (IgE)

Modern laboratory methods for allergy testing are based on the comparatively recent discovery that many allergies are mediated by immunoglobulins of the IgE class acting as points of contact between the allergen and specialized cells. The IgE molecules, which have a molecular mass of approximately 200 kd bind to the surface of mast cells and basophilic granulocytes. Subsequent binding of allergens to cell-bound IgE causes these cells to release histamines and other vasoactive substances, thereby initiating the events which we recognize as an allergic reaction.

In deciding on a Course of therapy, it is important to distinguish between IgE-mediated and non-lgE-mediated reactions. Measurement of the total circulating IgE level, in conjunction with other supporting diagnostic information, can aid in making this diagnosis. The supporting information should include appropriate tests for allergen-specific IgE. Measurement of the total circulating IgE level may also be of value in the early detection of allergy in infants, and as a means for predicting future atopic manifestations.

IgE levels normally show a slow increase during childhood, reaching adult levels in the second decade of life. In general, the total IgE level increases with the number of allergies which a person has and with the amount of exposure to relevant allergens.

Significant elevations may be encountered not only in sensitized individuals, but also in cases of IgE myeloma, pulmonary aspergillosis, and during the active stage of parasitic infestations.

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Immunoglobulins G,A,M (IgG, IgA, IgM)

The autoimmune disorders are a group of acquired diseases in which genetic factors appear to play a role. In autoimmune disease, the patient’s immune system reacts to normal components of the body as if they were foreign substances by producing antibodies (auto antibodies) against them. These diseases share certain clinical features and differentiation among them is often difficult. The most common findings associated with them include wide-spread immunologic and inflammatory alterations of connective tissue causing synovitis, pleuritis, myocarditis, endocarditis, pericarditis, peritonitis, vasculitis, myositis, skin rash and nephritis.

Generally, the autoimmune diseases are regarded as acquired diseases; however, their causes cannot be determined in most instances. Consequently, quantitation of specific protein assays, such as immunoglobulin G (IgG), immunoglobulin A (IgA),immunoglobulin M (IgM), C-reactive protein (CRP), and rheumatoid factor (RF), while not diagnostic of the underlying cause, can be used to assess disease activity and response to therapy.

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Insulin

Human insulin is a polypeptide hormone originating in the beta cells of the pancreas and serving as a principal regulator for the storage and production of carbohydrates. Its secretion is normally stimulated by increases in the amount of glucose in circulation. This leads to higher insulin levels and more rapid tissue-assimilation of glucose – followed by a decline in the insulin level as the glucose level subsides.

In a number of conditions, notably insulinoma and diabetes, this relationship is impaired. Insulin tends to circulate at inappropriately high levels in patients with insulin-secreting pancreatic tumors; such tumors can thus be a cause of hypoglycemia. Accordingly, insulin immunoassays  used sometimes in connection with provocative doses of tolbutamide or calcium, play an essential role in the identification (and localization) of insulinomas. The finding of fasting hypoglycemia in association with an inappropriately high serum insulin coentration is considered diagnostic.

Insulin levels do not figure in the subclassification of diabetes worked out by the National Diabetes Data Group. Nevertheless, when obtained in the course of a glucose tolerance test, they appear to be of some prognostic value in predicting the benefits of insulin therapy and the likelihood of progression to insulin-dependence and the complications (such as retinopathy) characteristic of  diabetes.

The application of insulin immunoassay to patients already undergoing insulin therapy is complicated by the fact that such therapy typically leads to the formation of anti-insulin antibodies capable of interfering with the assay. Some investigators have sought therefore to measure insulin in urine, or in serum samples subjected to column chromatography or PEG precipitation. But the measurement of “free” insulin remains of limited interest as a technique for – monitoring insulin therapy in the absence of statistics establishing therapeutic or toxic ranges. So far it appears that glucose control in diabetics cannot in general be achieved by normalizing the.insulin profile. Nor is it known at what point abnormally high insulin levels become dangerous.

Insulin assay also finds a significant diagnostic role in anovulatory hyperandrogenic women. Insulin resistance (an impaired glucose response to a specific amount of insulin) is frequently observed in association with polycystic ovarian disease in women. In many of these women normal glucose levels are maintained at the expense of increased circulating insulin to overcome the underlying defect. Elevated insulin perhaps acting through the IGF-1 receptors on the theca interstitial cells of the ovary produces excess androgens and induces dysovulation. Assessment of insulin levels in fasting and subsequently after glucose load may help identify these hyperinsulinemic anovulatory women

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L

Luteinising Hormone (LH)

Luteinizing hormone (Iutropin, LH), a glycoprotein of 28,000 daltons, is secreted by the anterior pituitary under the control of the hypothalamic gonadotropin releasing hormone (GnRH). LH consists of two polypeptide chains, alpha and beta. The alpha chains of LH, FSH, TSH and HCG are biochemically identical, whereas the beta chains are :biochemically unique, conferring bioactivity and biological and immunological specificity. In females, LH causes ovulation and steroid (estrogen and progesterone) production by the corpus luteum. Small quantities of LH are also necessary to promote estrogen production by the maturing follicle. In males, it stimulates interstitial (Leydig) cells to produce androgens and estrogens. Circulating levels of LH are controlled by a negative feedback effect on the hypothalamus by the steroid hormones. LH secretion, different for the two sexes and required for normal sexual function, occurs in pulses with rapid fluctuations over the entire reference range. Values for samples obtained in a single day from the same patient may therefore vary widely.

LH  measurements are used to define the hypothalamic-pituitary-gonadal axis. Serum gonadotropin determinations permit distinguishing between primary gonadal failure and deficient gonadal stimulation. If LH and FSH levels are elevated, primary gonadal failure is present, whereas if gonadotropin levels are low, deficient gonadal stimulation resulted in the hypogonadal state. LH measurement is also clinically important because LH and growth hormone are frequently the first hormones to be affected by pituitary disease.

Serum LH determinations have been very useful in the diagnosis and treatment of infertility in women. A midcycle rise is a good indication that ovulation will occur approximately 24 hours later. Subfertile couples, and women being treated with gonadotropins for infertility, can be informed that ovulation is imminent.

LH determination is also sometime in certain forms of dysovulatory infertility primarily polycystic overian (PCO) disease. In many PCO women LH:FSH ratio is increased, and under the influence of excess LH follicular theca cells produce excess androgenus and follicules become atretic and results is anovulation. 

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O

17-α-OH Progesterone

17α-Hydroxyprogesterone is a twenty-one carbon steroid ” produced in the adrenals – and also in the ovaries, testes and placenta – which serves as a biosynthetic precursor to cortisol. Its measurement is of value in the diagnosis and management of congenital adrenal hyperplasia, hirsutism and infertility. Circulating 17α-hydroxyprogesterone normally exhibits a diurnal pattern similar to that of cortisol, with higher values in the early morning than in the late afternoon. Hence, the time of collection should be standardized. Like progesterone, l7a-hydroxyprogesterone increases during the luteal phase of menstruating women and rises during pregnancy.

In the most common form of congenital adrenal hyperplasia, deficiency of the enzyme 21-hydroxylase blocks normal synthesis of cortisol, leading to a compensatory increase of ACTH secretion. This results in adrenal hyperplasia with increased levels of 17α-hydroxyprogesterone, DHEA and other adrenal steroids. Measurement of I7α-hydroxyprogesterone in blood samples collected on filter paper has been used to screen for congenital adrenal hyperplasia in newborns. In addition, serum measurements have been used in the differential diagnosis of hirsutism and infertility where 21-hydroxylase deficiency is suspected, since late-onset congenital adrenal hyperplasia can sometimes mimic the polycystic ovary syndrome. Untreated congenital adrenal hyperplasia in newborns is usually associated with markedly elevated 17α-hydroxyprogesterone levels ranging from 10 to 400 times the upper limit of normal, but lesser elevations may also occur. Some women with late-onset congenital adrenal hyperplasia may present modestly elevated basal 17α-hydroxyprogesterone levels (greater than 3 or4 ng/mL), but in others measurement of 17α-hydroxyprogesterone after ACTH stimulation may be required to demonstrate the disorder.

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P

Parathyroid Hormone, Intact (iPTH)

Parathyroid hormone (parathyrin, PTH), a single-chain polypeptide (molecular mass of ~ 9500 daltons) containing 84 amino acids, exerts significant influence in the maintenance of optimal calcium ion concentrations. PTH raises serum ionized calcium levels through direct action on bone and the kidneys: it increases the rate of calcium ion flow from bone to the extra cellular fluid, and increases both the renal tubular reabsorption of ionized calcium and the renal excretion of phosphate. Long-term regulation of total body calcium by PTH occurs through its stimulation of vitamin D metabolism, which results in enhanced intestinal absorption of ionized calcium.

In healthy individuals, PTH is secreted in response to circulating calcium ion levels. Any dip below an individual’s normal level triggers a pronounced increase in PTH secretion. Calcium levels returning to normal exert a negative feedback effect, thus inhibiting PTH secretion by the parathyroid glands.

PTH undergoes proteolysis to a lesser extent in the parathyroid glands but mostly peripherally – especially in the liver but also in the kidneys and bone – to yield N-terminal fragments and longer lived C-terminal and midregion fragments. The N-terminal fragment contains the region that confers bioactivity. For the intact hormone, the in vivo half-life is 2 to 5 minutes.

In hypercalcemia due to primary hyperparathyroidism or to ectopic PTH production (pseudohyperparathyroidism),the majority of patients have elevated PTH levels. By contrast, in hypercalcemia due to malignancy or other causes, the concentration of PTH in circulation is typically low or within normal reference range limits. PTH levels are also characteristically high in secondary hyperparathyroidism – usually associated  with renal failure – as a result of constant stimulation of the parathyroid gland by low calcium levels. Hypocalcemia accompanied by a low PTH level, on the other hand, is to be expected in hypoparathyroidism, either postsurgical or idiopathic.

Immunoassays specific for various PTH fragments have been developed. However, recent assays for intact PTH have the necessary sensitivity for detecting circulating intact PTH in normals and for discriminating between normals, those with primary hyperparathyroidism and nonparathyroidal hypercalcemic patients.

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Phenytoin

Phenytoin (5,5-diphenylhydantoin MW: 252.3 Da) is an antiepileptic drug widely used for treating several types of seizure. It is typically administered orally as phenytoin itself, or else by intravenous infusion (IV) or intramuscular injection (IM) of the prodrug fosphenytoin, a relatively water-soluble, phosphate ester of phenytoin. Depending on the route of administration, conversion of fosphenytoin to phenytoin is expected: to be essentially complete within 2 to 4 hours. Most of the phenytoin in circulation is tightly bound to plasma proteins, chiefly albumin. Normally, only about 10% circulates in the pharmacologically active free form, though in some conditions, such as renal failure, this fraction may increase to 30% or more. The amount circulating in free form is expected to be increased in hypoalbuminemia and in conditions where other compounds compete with phenytoin for protein binding sites. Examples include valproic acid and other anticonvulsants which may be administered concurrently with phenytoin; salicylates and nonsteroidal anti-inflammatory drugs such as oxaprozin as well as many other drugs which bind strongly to albumin. Likewise. high free fatty acid  levels may displace phenytoin from plasma proteins.

Phenytoin is cleared through the liver, where it is converted primarily to 5-(p- hydroxyphenyl)-5-phenylhydantoin, which is subsequently glucuronidated and excreted in the urine.  Though inactive, these metabolites-HPPH and its glucuronide HPPG – are structurally similar to phenytoin and may compete with phenytoin for protein binding sites. The clearance rate declines somewhat with age, and is reduced in renal insufficiency. Drugs enhancing or inhibiting the liver’s ability to metabolize phenytoin can be expected to affect circulating levels. Moreover, metabolic capacity is limited; hence the relationship between dosage and circulating levels is not uniform: at higher levels, even within the therapeutic range, small increases in administered dose may result in large increases in circulating levels.

Phenytoin is commonly monitored by immunoassay because (total) circulating levels of the drug correlate more strongly with therapeutic effect and toxicity than does the administered dose. The generally accepted therapeutic range for total circulating phenytoin is 10 to 20 μg/mL(40 to 80 μmol/L), but these limits should be considered as guidelines only.  (There is no established range for free circulating phenytoin.) Dosage optimization must take into account the patient’s clinical response to the drug. Low levels may be associated with inadequate control, as manifested in the frequency and/or severity of the seizures. High levels may be associated with symptoms of Ineurotoxicity – including involuntary rhythmic eye movements (nystagmus),  nausea, vomiting, impaired coordination (ataxia), speech interference (dysarthia), severe lethargy, and so on – or even with  a worsening of the seizures.

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Progesterone

Progesterone is a steroid hormone which plays an important role in the preparation for and maintenance of pregnancy. It is synthesized from cholesterol via pregnenolone – then rapidly metabolized to pregnanediol, for the most part, in the liver. The ovary and placenta are the major production sites; but a small amount is also synthesized by the adrenal cortex in both men and women.

Circulating progesterone levels, which are characteristically low during the follicular phase, increase sharply during the luteal phase of menstrual cycles, reaching a maximum some 5 to 10 days after the midcycle LH peak. Unless pregnancy occurs, a steep decline to follicular levels sets in about 4 days before the next menstrual period. This pattern constitutes the rationale behind the well-established use of serum progesterone measurements as a simple and reliable method for ovulation detection.

There is growing literature on luteal phase defects. Daily progesterone levels are considered the most accurate means for documenting a defective luteal phase. However, some investigators have found that three samples or even a single sample (if well timed) can provide valuable information on the adequacy of the luteal phase.

Measurements of serum progesterone have also been used to check the effectiveness of ovulation induction, to monitor progesterone replacement therapy and to detect and evaluate patients at risk for abortion during the early weeks of pregnancy. On the other hand, although progesterone levels increase throughout pregnancy, they are not considered a suitable means for monitoring fetal well-being during the third trimester.

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Prolactin

Human prolactin is a polypeptide hormone of the anterior pituitary with a molecular mass of about 22 kd. It plays an essential role in the secretion of milk and has the ability to suppress gonadal function. Determination of prolactin is an important tool in the investigation of amenorrhea, galactorrhea and hypothalamic-pituitary disorders.

As a reference range for circulating prolactin, the literature suggests concentrations up to approximately 20 ng/mL. Values are distinctly elevated at birth but decline to adult levels in less than three months. Women are reported to have slightly higher mean levels than men, with a slight rise at puberty – apparently estrogen related – and a corresponding fall at menopause. During pregnancy, the prolactin level climbs steadily to ten or twenty times its former value, then drops back down to normal after delivery – within three weeks in nonnursing mothers. In those who breast-feed, the decline to normal is more gradual because of the prompt and dramatic surges in prolactin release induced by suckling. Women taking oral contraceptives or under estrogen treatment may have prolactin levels higher than normal.In assessing the significance of moderate elevations, it is important to keep in mind that prolactin is a stress hormone. Not only surgery, but events no more distressing than venipuncture or a clinical interview have been reported to occasion a transient rise. Moreover, the release of prolactin is inherently episodic, and day- to-day fluctuations with CVs as high as 30% have been encountered. Finally, there is a sleep-related diurnal variation: prolactin levels increase during sleep and reach their lowest a few hours after waking. The advice sometimes given to draw samples “between nine and noon” is based on the assumption that subjects observe reasonably normal waking hours.

Under normal circumstances the 22 kd  prolactin predominates, however, prolactin may also be produced in higher molecular mass forms (50-150 kd). These prolactins have markedly reduced bioactivity. In certain forms of macroprolactinemia the high mw prolactin variant may represent 85% or more of the total prolactin. Because of difference in the binding affinity and avidity between the macroprolactins and the employed antibody in an assay (it is desirable that macroprolactins should have negligible cross-reactivity with the antibody), results of commercial prolactin assays in the presence of macroprolactis may widely differ between different assay systems and, therefore, between the laboratories.

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Prostate-Specific Antigen (PSA), Total

Prostate specific antigen (PSA) is a glycoprotein monomer with protease activity. PSA has an isoelectric point of approximately 6.9 and a molecular weight of approximately 33-34 kilodaltons; it contains approximately 10% carbohydrate by weight. The amino acid sequence of PSA was reported, and the gene has been cloned. PSA is biochemically and immunologically distinct from Prostatic Acid Phosphatase (PAP) and does not exhibit enzymatic phosphatase activity.

PSA is localized in the cytoplasm of prostatic ductal epithelium and in secretions of the ductallumina. Because PSA is a secretory protein of the prostate, it can be recovered and purified both from prostatic tissue and from seminal plasma. PSA has been found to be exclusively associated with prostate tissue; an elevated serum PSA has been found In patients with prostate cancer, benign prostatic hypertrophy, and inflammatory conditions of other adjacent genitourinary tissues, but not in healthy men, men with nonprostatic carcinoma, healthy women or  women with cancer.  Measurement of serum PSA is not suitable as a screen for prostate cancer because elevated PSA concentrations are also observed in patients with benign prostatic hypertrophy; nor is it recommended as a guide in disease staging. The combination of PSA measurement and rectal examination with ultrasonography, in the event of abnormal findings, may provide a better method of detecting prostate cancer than rectal examination alone. Determinations of total immunoreactive PSA can be useful in detecting metastatic or persistent disease in patients following surgical or medical treatment of prostate cancer. Persistent elevation of PSA following treatment or an increase in the pretreatment PSA concentrations is indicative of recurrent or residual disease. Hence, PSA is widely accepted as an aid in the management of prostate cancer patients.

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R

Rubella Antibodies

Rubella, also known as German measles,occurs throughout the world. The prodromal stage includes malaise and a low-grade fever, followed by characteristic lymphadenitis and finally a macular or maculopapular rash. While rubella is primarily an infection of children, rubella infections during the first trimester of pregnancy can result in congenital infections with disastrous consequences. Birth defects, such as deafness and/or congenital heart defects are the most common. Multiple defects such as mental retardation, cataracts and hepatosplenomegaly may also occur and contribute to death of the infant in the first year of life. Infants with congenital infections may secrete virus for up to two years. Contact with these children poses a risk to susceptible pregnant women.

Clinical symptoms of rubella infection are frequently mild or nonspecific, making the infection difficult to diagnose clinically.For these reasons, pregnant women with an undiagnosed illness with rash should be evaluated for the possibility of an acute, primary rubella infection. While the virus can be cultured in vitro, serology remains the principal means for , establishing a clinical diagnosis of acquired rubella and congenital infections. As two-thirds of defects are not apparent at birth, it is recommended that children exposed in utero be monitored for clinical and serological status until school age. A rubella vaccine, introduced in 1969. has significantly lowered the incidence of both acute disease and congenital rubella syndrome: However, as the vaccination program may vary with geographical location and as the level of immunity provided by vaccination is not always adequate, pregnant women and women of child-bearing age are routinely screened for immune status.

The presence of rubella IgG antibodies indicates a previous vaccination or infection and is indicative of presumptive immunity. Patients suspected of having primary, acute rubella infection should be tested for the presence of IgM antibodies.

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T

Testosterone, Total & Free

In the male, testosterone is mainly synthesized in the interstitial Leydig cells of the testis, and is luteinizing hormone of the anterior pituitary. Testosterone is responsible for the development of secondary sex characteristics, such as the accessory sex organs, the prostate, seminal vessicles and the growth of facial, pubic and axillary hair. Testosterone measurements have been very helpful in evaluating hypogonadal states. Increased testosterone levels in males can be found in complete androgen resistance (testicular feminization). Common causes of decreased testosterone levels in males include: hypogonadism, orchidectomy, estrogen therapy, Klinefelter’s syndrome, hypopituitarism, and hepatic cirrhosis. In the female, testosterone comes from three sources. It is secreted in small quantities by both the adrenal glands and the ovaries, and in healthy women 50-60% of the daily testosterone production arises from peripheral metabolism of prehormones, chiefly androstenedione. Assessment of testosterone measurement finds a major role in women with dysovulatory infertility, hirsutism, polycystic ovarian disease and related hyperandrogenic states.

Testosterone circulates almost entirely bound to transport proteins: normally less than one percent is free. The principal transport protein for testosterone is known as sex hormone binding globulin (SHBG) or testosterone-estradiol binding globulin(TeBG),since it binds not only to testosterone but also to estradiol (and dihydrotestosterone). Albumin and cortisol binding globulin (CBG) are the other testosterone transport proteins. For three reasons, SHBG is the most important of these transport proteins. It carries, at least in females, a higher percentage of the testosterone in circulation than either albumin or CBG. Furthermore, it binds to testosterone with a much higher affinity than do the other two transport proteins. (The testosterone bound to albumin and CBG is collectively known as “weakly bound” testosterone.) Finally, SHBG has a responsiveness, not associated with albumin, insofar as the SHBG level is sensitive to changes in the ratio of circulating estrogens to circulating androgens. SHBG thus plays a greater role in determining the level of free testosterone in circulation.

In pregnancy, SHBG levels show a progressive increase that mirrors the rise in estradiol levels. Although the total testosterone level also shows some increase during pregnancy, the rise in estradiol, and hence also in SHBG, is more dramatic. The net result is a decrease in free testosterone as a percent of total testosterone. Women taking oral contraceptives likewise have increased SHBG levels, at least if they are taking high dose ethinyl estradiol preparations. Conversely, the administration of androgens to prepubertal boys, or the elevation of endogenous testosterone by HCG stimulation, induces a significant decrease in the SHBG level. Obesity is also associated with a decrease in the SHBG level.

Other things being equal, we expect the concentration of free testosterone in circulation to increase if the testosterone level (T) increases or if the SHBG level decreases. The T/SHBG ratio, ie. the ratio of total testosterone to (the concentration or binding capacity of) SHBG, thus serves as a rough guide to the concentration of free testosterone in circulation. The T/SHBG ratio is sometimes referred to as the Testosterone Free Index (TFI).

The Testosterone Free Index is often increased in severe acne, male androgenic alopecia (balding), hirsutism and other conditions. A low SHBG level, often in combination with a normal total testosterone level, is a common finding in these conditions. An increase in the testosterone production rate typically induces a decrease in the SHBG level. This stimulates cellular uptake and metabolism of testosterone, by making more available in the free form. The result is that the total testosterone level is often normal, because the increased production rate is offset by an increased rate of clearance.

Total testosterone measurements have traditionally been used to help screen for hirsutism. In view of the mechanism just described, it is natural to expect free testosterone levels, measured directly or indexed by the T/SHBG ratio, to correlate better with hirsutism. It is therefore logical to measure free testosterone, rather than total testosterone, for the assessment of true androgenic status.

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Thyroglobulin

Thyroglobulin (TG) is a heterogeneous iodoglycoprotein which has a molecular mass of approximately 660,000 daltons. Thyroglobulin is normally synthesized in the follicular cells of the the thyroid gland, under the influence of thyrotropin and represents the precursor to thyroxine and the other iodothyronines. The expected upper limit of normal for circulating thyroglobulin is approximately 40 to 60 ng/mL, with a median of 5 to 10 ng/mL. Somewhat higher values are encountered in new borns and during the third trimester of pregnancy. Thyroglobunin levels also tend to be elevated in regions of endemic goiter. The major clinical applications for measurement of this prohormone is derived from the fact that functioning thyroid tissue appears to be the only source of circulating thyroglobulin. Accordingly, thyroglobulin determinations have been widely used to complement radioiodine scanniog and other technique (such as ultrasound or immunohistocbemical staining) as an aid in identifying the presence or absence of functioning thyroid tissue, or an increase in such tissue relative to an individually established baseline. The differential diagnosis of congenital hypothyroidism is a well-established context of use for this application of serum thyroglobulin measurement Congoniltal hypothyroidism.

Thyroglobulin determinations have been used, sometimes in conjunction with ultrasound and radioiodine scanning, to help clarify the type of thyroid defect in previously diagnosed congenital hypothyroidism. Very low or undetectable thyroglobulin levels are expected in infants born without thyroid tissue (thyroid agenesis), whereas higher, but widely varying levels are generally encountered in infants with hypoplastic thyroid gland, ectopic thyroid tissue, dyshormonogenic goiter, congenital TBG deficiency or trasient hypothyrodism.

Thyroglobulin measurements may also be value in helping to distinguish subacute thyroiditis from thyrotoxicosis caused by cover administration of thyroid hormones. In te lattr event low levels of thyroglobulin are expected due to thyroid hormone suppression of thyrotropin.

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Thyroglobulin Antibody (Anti-TG)

Thyroglobulin is produced only by the thyroid gland and is a major component of the thyroid follicular colloid. The thyroid hormones 3,5,3′,5′-tetraiodothyronine (thyroxine, T4) and 3,5,3′-triiodothyronine (T3) are synthesized from thyroglobulin.  Autoantibodies to thyroglobulin (TG autoantibodies) are often present in patients with autoimmune thyroid disease. Approximately 10 percent of healthy individuals have TG autoantibodies at low levels; higher concentrations are found in 30 and 85 percent of patients with Graves’ disease and Hashimoto’s thyroiditis, respectively. Elevated levels of antibodies to thyroid peroxidase (TPO autoantibodies) occur more frequently than high anti-TG levels in these diseases. However, anti-TG determinations therefore do not seem to add to the diagnostic information provided by anti- TPO results.

TG autoantibody measurements are most useful for evaluating samples submitted for thyroglobulin measurements because TG autoantibodies can interfere with both competitive immunoassays and immunometric assays for thyroglobulin.

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Thyroid Peroxidase Antibody (Anti-TPO)

Antithyroid peroxidase (TPO) antibodies are autoantibodies directed against the thyroid peroxidase enzyme. This enzyme catalyzes the iodination of tyrosine in thyroglobulin during the biosynthesis of T3 and T4.

Historically, these antibodies were referred to as antimicrosomal antibodies (AMA) because the antibodies bind to the microsomal part of the thyroid cells. Recent research has identified thyroid peroxidase as the primary antigenic component of microsomes. Thyroid autoimmune disease is the major factor underlying hypothyroidism and hyperthyroidism and tends to occur in a genetically predisposed population. 

The major thyroid autoimmune diseases are Hashimoto’s thyroiditis and Graves’ disease. In virtually all cases of Hashimoto’s disease and in the majority of Graves’ disease, TPO autoantibodies are elevated. High levels of TPO autoantibodies, in the context of the clinical presentation of hypothyroidism, confirms the diagnosis of Hashimoto’s disease.

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Thyroid Stimulating Hormone (TSH Ultrasensitive)

Thyroid stimulating hormone (thyrotropin, TSH) is a pituitary hormone which, through its action on the thyroid gland, plays a major role in maintaining normal circulating levels of the iodothyronines, T4 and T3. TSH is controlled by negative feedback from circulating T4 and T3, and by the hypothalamic hormone TRH (thyrotropin releasing hormone).

In primary hypothyroidism, where there is impaired production of thyroid hormones, the TSH level is typically highly elevated. In secondary or tertiary hypothyroidism, on the other hand, where thyroid hormone production is low as a consequence of pituitary or hypothalamic lesions, the TSH level is usually low. In hyperthyroidism, the TSH level is typically suppressed to subnormal levels. Less often, this condition may result from hyperstimulation of the thyroid, due to hypothalamic or pituitary lesions, in which case the TSH level is usually increased.

Measurement of circulating TSH has been used as a primary test for differential diagnosis of hypothyroidism and as an aid in monitoring the adequacy of thyroid hormone replacement therapy. It should be remembered that hyperthyroidism and hypothyroidism are graded conditions. This implies that not all patients in these disease categories can be expected to have TSH levels far outside the euthyroid range. On the other hand, TSH levels exit the euthyroid reference range in the very early phases  developing thyroid disease, while the patient’s disease is still subclinical and thyroid hormone levels remain within their  euthyroid reference ranges.

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Thyroxine (T4), Free

The principal thyroid hormone, thyroxine (T4), circulates almost entirely bound to carrier proteins, chief of which is thyroxine-binding globulin (TBG). Altered carrier protein concentrations induce changes in total T4levels, and free T4 concentrations tend to stay within a tight range. For this reason, total T4 measurements do not always reflect thyroid status. TBG levels may vary under different physiological conditions, such as during pregnancy, oral contraceptive use, and estrogen therapy. Total T4 1evels may increase above the normal range while free T4 remains normal. Alternatively, patients with a dysfunctional thyroid gland and altered TBG levels can have normal total T4levels, masking the illness. Since abnormal T4 1evels may signify either abnormal thyroid function or carrier protein variation (physiological or pathological), free T4 measurements more highly correlate with thyroid status than total T4 measurements.

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Toxoplasma Antibodies-IgG,IgM (Toxo IgG & IgM)

Toxoplasma gondii is an obligate intracellular parasite capable of infecting most mammals, including humans. The organism is transmitted through ingestion of insufficiently cooked meat. Throughout the world, 1 to 90 percent of populations may be infected, with 25 to 30 percent of the adult population infected in the United States. While toxoplasmosis may be manifested in several forms, infections are usually clinically not apparent, and latent infections usually persist for life. Overt clinical symptoms are similar to infectious mononucleosis, with lymphadenopathy, fever, headache, malaise and sometimes pneumonia and myocarditis.

As with other latent infections, acute toxoplasma infection can pose a serious threat to immunocompromised individuals and newborns who acquire the infection in utero. Immuno-suppressed patients may develop encephalitis, myocarditis or pneumonitis. Congenital infections usually result as a consequence of asymptomatic acute maternal infection. This infection can cause premature delivery, spontaneous abortion or stillbirth. Neonates may manifest chorioretinitis, hydrocephaly, microcephaly, cerebral calcification and psychomotor retardation. The majority of congenitally infected children will not exhibit any symptoms until later in life. Management of toxoplasmosis requires serological monitoring of infected individuals as the organism is not readily available for culture. Quantitative testing for the presence of toxoplasma IgG can be useful to determine prior infection and indicate reactivation of the infection. Qualitative testing for the presence of toxoplasma IgM is useful to determine acute infection. Accurate diagnostic information is important, particularly during pregnancy, as treatment with spiramycin can reduce the  risk to the fetus.

Accurate diagnostic information is important, particularly during pregnancy, as treatment with spiramycin can reduce the risk to the fetus.

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Tri-Iodothyronine (T3), Free

Under normal physiological conditions triiodothyronine (T3) represents approximately 5 percent of the thyroid hormone in plasma. Although present in lower concentration than thyroxine (T4), T3 has greater metabolic activity, faster turnover and a larger volume of distribution. It is produced largely through extrathyroidal conversion of T4. Like T4, it circulates almost entirely bound to the carrier proteins TBG, pre-albumin and albumin. Free T3 constitutes only about 0.25% of the total T3 in circulation.

Measurement of total T3 by immunoassay has a number of well-established uses. In the presence of elevated free or total T4, T3 measurements help confirm a hyperthyroidism diagnosis. Abnormal elevation of total T3 may also occur when the total T4 concentration is normal- a condition known as “T3 toxicosis”.

For the most part, free T3 levels correlate closely with total T3 levels. Total T3, however, depends not only on thyroid status and the peripheral conversion of T4 to T3, but also on the concentration of thyroid hormone-binding proteins. Free T3, on the other hand, is largely unaffected by variations in these carrier proteins. Thus, the TBG elevations typical of pregnancy, oral contraceptive use, and estrogen therapy effects an increase in the total T3 level while leaving the free T3 concentration basically unchanged. The free T3 concentration therefore typically reflects a patient’s actual status more reliable than the total T3 concentration.

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Tri-Iodothyronine (T3), Total

Under normal physiological conditions, T3 represents approximately 5 percent of the thyroid hormones in serum. Although present in lower concentration, T3 has a greater intrinsic metabolic activity, faster turnover and larger volume of distribution than circulating T4. Reports that thyrotoxicosis may be caused by abnormally high concentrations of T3, rather than T4, have reinforced the importance of T3 measurements. In addition, T3 determination is an important tool for monitoring hypothyroid patients receiving sodium liothyronine therapy. Unlike “T3 Uptake” tests, which estimate the saturation of thyroid hormone binding proteins, total T3 analysis actually measures circulating levels of triiodothyronine. Most reports indicate that T3 levels distinguish clearly between euthyroid and hyperthyroid subjects, but , provide a less clear-cut separation between hypothyroid and euthyroid subjects.

Numerous conditions unrelated to thyroid disease may cause abnormal T3 values. Consequently, total T3 values should not be used on their own in establishing the thyroid status of an individual. The levels of serum T4, TBG (thyroid binding globulin), TSH (thyroid stimulating hormone) and other clinical findings must be considered as well.

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Triple Screening

According to the American College of Obstetricians and Gynecologists, it has become standard in prenatal care to offer screening tests for neural tube defects and genetic abnormalities. There have been some changes in the recommended method of prenatal screening over the past few years, and research to improve detection rates with better combinations of maternal serum analytes is ongoing. The issues facing physicians are the sensitivity and specificity of multiple serum analyte combinations. The current maternal serum analytes in use in most areas are alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG) and unconjugated estriol. Measurement of AFP alone can detect the vast majority of neural tube defects (NTDs) and a small portion of trisomy 21–affected pregnancies in patients of all ages. Adding hCG and unconjugated estriol to this screen increases the rate of detection of tri-somies 21 and 18. Counseling patients about the risks and benefits of such screening is important to provide a balanced discussion of screening issues.

Interpreting Triple Analyte Screening Results

Anomaly

AFP

hCG

uE 3

NTDs

Increased

Normal

Normal

Trisomy 21

Decreased

Increased

Decreased

Trisomy 18

Decreased

Decreased

Decreased

 
 

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V

Valproic Acid

Valproic acid is used primarily in the treatment of simple and complex absence seizures. It can be administered alone or in combination with other drugs such as phenobarbital or phenytoin. Valproic acid increases the concentration of γ-amino- butyric acid (GABA) by inhibiting GABA transaminase. GABA is a potent inhibitor of pre- and postsynaptic discharges in the central nervous system. Valproic acid circulates mainly bound to protein. It competes with phenytoin for protein-binding sites. Valproic acid also inhibits the renal clearance of phenobarbital. When these two drugs are used in combination, the concentration of phenobarbital can be increased by up to  40 percent. Valproic acid is rapidly and almost completely absorbed after oral administration, reaching its peak concentration after 1 to 2 hours. In adults, its half-life is 16 hours. The therapeutic range for valproic acid is 50 to 100 μg/mL. Levels above 100 μg/mL are considered toxic. Plasma concentrations should be monitored to help maintain an effective dosage and prevent side effects caused by an excessive concentration.

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Vitamin B12

Vitamin B12 (cobalamin) and folate are nutrients essential to hematopoiesis. Megaloblastic anemia is almost always due to lack of one of these two vitamins. Vitamin B12 deficiency can also result in severe neurological impairment. Circulating levels of vitamin B12 are usually a good index to tissue stores. That is, vitamin B12 levels as measured in serum or plasma by an optimized assay system are typically low in vitamin B12 deficiency, and normal or elevated otherwise. Exceptions to this rule can occur in those relatively uncommon situations where levels of vitamin B12 transport proteins are abnormal. Thus, low circulating vitamin B12 levels can occur in the absence of vitamin B12 deficiency where the level of Transcobalamin-I (a physiologically inactive transport protein) is low. Conversely, vitamin B12 deficiency can occur in the presence of normal or even elevated plasma vitamin B12 levels, where transcobalamin-II levels are low or where levels of inactive vitamin B12 transport proteins are high, as in chronic myelogenous leukemia.Circulating folate levels are usually normal or elevated in vitamin B12 deficiency, but red cell folate levels are frequently low in this condition.

Vitamin B12 deficiency occurs only rarely as a result of dietary lack of this vitamin. More commonly, it results from impaired absorption, as in partial or total gastrectomy, or in pernicious anemia, a condition characterized by absence or near absence of intrinsic factor. Since roughly two thirds of all patients with pernicious anemia have blocking antibodies to intrinsic factor (IFbAb), while IFbAb are only very rarely encountered in other situations, IFbAb determinations represent a useful follow-up test for the differential diagnosis of vitamin B 12 deficiency. (Circulating intrinsic factor antibodies are present in more than half of all pernicious anemia patients. Increased transport protein levels can occur, for example, in chronic myelogenous leukemia.)

Common causes of high vitamin B12 levels include liver disease, myeloproliferative disease (with chronic myelogenous leukemia as a special case) and the use of multivitamin supplements.

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