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tests at Central Laboratory T - Z
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T lymphocyte CD3+, CD4+ & CD8+ subsets
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printPurpose and scope
Lymphocytes can be subdivided into 3 major sub-populations, based on their functions and antigen expression: T lymphocytes, B lymphocytes, and natural killer lymphocytes. T lymphocytes (CD3+) are further subdivided into: suppressor/cytotoxic (CD8+); and helper/inducer (CD4+).
Determining the percentages or absolute counts of these subsets of cells is important in the monitoring and therapy of immunodeficiency (eg HIV) and autoimmune diseases. In clinical trials, we measure T lymphocytes and their subsets as biomarkers of the effects of drugs on immune function.Method
Flow cytometry using antibodies to cell-specific markers
Sample requirements
Collect blood by venepuncture into a sterile K3 EDTA Vacutainer tube. Store blood samples at room temperature, and stain them within 48 h of collection. Analyse them within 24 h of staining.
On receipt of a sample, do a white blood cell (WBC) count. To ensure linearity of the T lymphocyte assay, WBC should be between 0.2 x 109 and 29.7 x 109/L, and lymphocyte counts should be between 0.1 x 109 and 9.0 x 109 /L. If the counts are not within the above ranges, add an appropriate comment to the report.Maximum turnaround time
Batched
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Testosterone (free)
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printAlternative test name
FTEST
Purpose and scope
Testosterone is an androgen secreted by the Leydig cells of the testes, and its production increases during puberty. Women produce about 5–10% as much testosterone as do men.
Testosterone directly affects development of male secondary sexual characteristics. Also, it is converted to an active metabolite, dihydrotestosterone, in the target organs. Circulating testosterone concentrations are elevated in women with hyperandrogenism, in the presence or absence of polycystic ovarian disease.
About 60% of blood testosterone is normally bound with high affinity to sex hormone-binding globulin (SHBG); of the remainder, 1–2% is loosely bound to albumin. Both the albumin-bound and free fractions represent the biologically active fraction, while SHBG effectively inhibits testosterone's action.
Measurement of the free or unbound fraction of serum testosterone is a means of estimating the physiologically active hormone. In clinical trials, we measure free testosterone: to ensure that potential subjects are eligible for a trial; as a pharmacodynamic marker; or as a pharmacokinetic variable.Method
Solid-phase competitive assay
Sample requirements
Serum. If necessary, store serum at 2–8°C for up to 24 h, or at –20°C for up to 2 months, before assay.
Maximum turnaround time
Batched
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Testosterone (total)
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printPurpose and scope
The pituitary gonadotrophins, luteinising hormone (LH) and follicle-stimulating hormone (FSH), control the function and secretion of oestrogens, progesterone, and testosterone. In addition, LH and FSH regulate the development of ovarian follicles in females, and FSH stimulates spermatogenesis in males. LH and FSH secretion is in turn regulated by the hypothalamic gonadotrophin releasing hormone (GnRH).
In the male, pulses of GnRH stimulate FSH and LH secretion from the pituitary. FSH stimulates in the Sertoli cells in the seminiferous tubules of the testis to produce mature sperm. LH stimulates testosterone production from Leydig cells in the testis. Testosterone aids spermatogenesis, and is responsible for the male secondary sexual characteristics. It is also an anabolic hormone. Testosterone inhibits pituitary GnRH secretion. In healthy women, testosterone levels are low. Testosterone is mainly bound to sex hormone-binding globulin (SHBG).
In the trials of new medicines, testosterone is not routinely measured. Testosterone may be measured if the study medicine is expected to affect blood levels of testosterone.Method
competitive binding immunoenzymatic method
Sample requirements
Serum or heparin plasma. Samples are stable for 8 h at room temperature, 48 h at 2–8°C, or for 6 months at –20°C.
Maximum turnaround time
24 h
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Thrombin time
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printAlternative test name
TT
Purpose and scope
Thrombin time (TT) is a measure of the integrity of blood coagulation system and reflects a deficiency of fibrinogen, or inhibition of thrombin. Drugs, and deficiencies and abnormalities of coagulation factors, are the causes of a prolonged TT. In clinical trials of new medicines, the TT serves as a marker for drug effects on blood coagulation. In some studies, that effect might be an intended pharmacodynamic one.
Method
Absorbance
Sample requirements
109 mmol/L buffered sodium citrate plasma with a 9:1 ratio of blood to citrate. For long-term storage, keep samples at –40°C for a maximum of 2 months.
Maximum turnaround time
24 h
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Thyroid stimulating hormone
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printAlternative test name
TSH
Purpose and scope
TSH is released from the anterior pituitary gland and regulates the synthesis of thyroid hormones. TSH synthesis and release is controlled by thyrotrophin-releasing hormone (TRH), which is produced by the hypothalamus. A rise in thyroid hormone levels inhibits the pituitary response to TRH and a fall in thyroid hormone levels causes an increase in TRH and TSH.
In clinical practice, TSH is used to diagnose and monitor the effectiveness of treatment in thyroid dysfunction. TSH is elevated in primary hypothyroidism and low in secondary and tertiary hypothyroidism. TSH is normally suppressed in hyperthyroidism. In early clinical trials of new medicines, TSH is measured to confirm euthyroid status before entry. Also, serial measurements may be done if the trial medicine is expected to affect the hypothalamic-pituitary-axis.Method
Two-site immunoenzymatic ‘sandwich' immunoassay
Sample requirements
Serum, or plasma (heparin). Samples are stable for 8 h at room temperature, 48 h at 2–8°C, or for 6 months at –20°C.
Maximum turnaround time
24 h
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Thyroxine (free)
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Free T4, FT4
Purpose and scope
Free thyroxine (FT4) is synthesised in and secreted from the thyroid gland under the control of thyroid stimulating hormone (TSH).
In clinical practice, measurement of FT4 is used to diagnosis thyroid dysfunction. FT4 is usually elevated in hyperthyroidism (but may be normal in T3 thyrotoxicosis) and reduced in hypothyroidism. In early clinical trials of new medicines, FT4 is measured to confirm euthyroid status before entry to the trial. Also, serial measurements may be done if the study medicine is expected to affect the hypothalamic-pituitary-axis.Method
Two-step enzyme immunoassay
Sample requirements
Serum or heparinised plasma. Samples are stable for 8 h at room temperature and 48 h at 2–10°C. Freeze samples at –20°C for longer storage.
Maximum turnaround time
24 h
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Thyroxine (total)
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Total T4, TT4
Purpose and scope
The hypothalamus produces thyrotropin releasing hormone (TRH), which stimulates the synthesis and release of thyroid stimulating hormone (TSH) by the pituitary gland. In turn, TSH binds to receptors in the thyroid gland, resulting in the synthesis, storage, secretion and metabolism of triiodothyronine (T3) and thyroxine (T4).
99% of T3 and T4 in the blood is bound to serum proteins, and is biologically inactive. Free T3 and T4 bind to receptors in target tissues, thereby regulating body temperature, carbohydrate metabolism and some aspects of lipid and vitamin metabolism. T3 is up to 9 times more biologically active than T4. About 80% of T3 is not secreted directly by the thyroid, but is derived by the enzymatic removal of an iodine atom from T4, mainly in the liver.
The clinical importance of total serum T4 measurement is in the diagnosis of thyroid disorders. Serum concentrations of T4 are higher than normal in Grave's disease, and most other types of hyperthyroidism, and are reduced in primary hypothyroid diseases such as Hashimoto's thyroiditis and neonatal hypothyroidism. In clinical trials of new medicines, total T4 serves as a marker of drug effects on thyroid function.Method
Competitive binding immunoenzymatic assay
Sample requirements
Serum or plasma (heparin). Samples are stable for 8 h at room temperature, and for 24 h at 2–8°C. Freeze samples at –20°C or colder for longer storage.
Maximum turnaround time
24 h
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Total protein
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printPurpose and scope
Blood contains many proteins, the most abundant of which are albumin and immunoglobulins. Other blood proteins include fibrinogen, complement proteins, peptide hormones, blood clotting factors, enzymes, and the α and β-globulins. Although total protein is a measure of all the proteins in blood, albumin and immunoglobulins are the most important. Hypoproteinaemia is almost always due to hypoalbuminaemia. Fluid loss can cause relative hyperalbuminaemia, and hence hyperproteinaemia. Hyperproteinaemia with a normal albumin is usually due to an increase in immunoglobulins. In clinical trials of new medicines, total protein is used as a screening test for underlying disease, and as an indicator of haemodilution.
Method
Timed-endpoint biuret method
Sample requirements
Serum or plasma (lithium or sodium). Centrifuge the samples within 2 h of collection. Samples are stable for 4 h at room temperature, or 3 days at 2–8ºC. Samples can be frozen at –20°C for up to 6 months. Once thawed, do not refreeze.
Maximum turnaround time
24 h
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Total protein (urine)
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printPurpose and scope
Urine contains traces of many proteins; albumin constitutes about one third of the total. Other urine proteins include α-, β-, and γ-globulins, and immunoglobulin A (derived from secretions of the urinary tract), and enzymes and proteins from the tubular epithelial cells and leucocytes. The amount of a particular protein in the urine depends on the extent of its reabsorption by the renal tubules; that is inversely proportional to molecular size.
Measurement of total protein aids in the diagnosis and treatment of diseases associated with disordered renal, cardiac and thyroid function. There are 4 main types of proteinuria: a) glomerular proteinuria (resulting from increased glomerular permeability); (b) tubular proteinuria (resulting from defective tubular reabsorption); (c) overload proteinuria (resulting from increased concentration of low molecular weight protein); and (d) postrenal proteinuria (resulting from abnormal secretion of protein into the urinary tract). Increased urinary protein may also be due to strenuous exercise, nephritis, diabetic nephropathy, or urinary tract infections.
In clinical trials of new medicines, urine total protein serves as a marker of renal toxicity.Method
Enzymatic reaction rate
Sample requirements
Urine. Samples are stable for up to 48 h at 2–8°C.
Maximum turnaround time
24 h
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Transferrin
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printPurpose and scope
Transferrin is the principal plasma protein for the transport of iron. It has 2 binding sites for iron: they are strong at physiological pH, but weaken with decreasing pH. Transferrin is synthesised in the liver and, to a smaller extent, in the reticuloendothelial system and endocrine glands, such as the testes and ovaries.
In clinical trials, measurement of plasma transferrin concentrations is useful for the differential diagnosis of anaemia: concentrations rise in iron deficiency anaemia. In congenital atransferrinaemia, a very low level of transferrin is accompanied by iron overload and a severe hypochromic anaemia resistant to iron therapy. High concentrations of transferrin occur in pregnancy, and during oestrogen administration. Concentrations decrease in conditions associated with protein loss, such as nephrotic syndrome; and in protein-deficient states such as malnutrition, and chronic liver disease.Method
Enzymatic reaction rate
Sample requirements
Serum and EDTA, or heparinised plasma. Transferrin is stable in serum and plasma for 8 months when stored at 2–8°C, and for 4 months when stored at
15–20°C.Maximum turnaround time
24 h
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Triglycerides
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printPurpose and scope
Fats are insoluble in water, and are transported in the blood stream as protein-lipid complexes (lipoproteins) that contain cholesterol, cholesterol esters and triglycerides. Triglycerides contain glycerol which has been esterified with 3 fatty acids. The glycerol may be of dietary origin (from animal products), or synthesised in the liver. Dietary triglycerides are transported mainly in chylomicrons; endogenously synthesised triglycerides are transported mainly in very low density lipoprotein (VLDL) particles. The pathways regulating triglyceride concentrations are major targets for therapeutic agents.
Triglycerides are a major risk factor for disease, eg atherosclerosis. In early clinical trials of new medicines, serum triglycerides are measured to identify people with disorders of lipid metabolism, or people with raised triglyceride concentration, who may be at risk of coronary heart disease. Triglycerides may also help to show whether a subject is in the fasted or post-prandial state, as their concentration increases after meals.Method
Timed endpoint method
Sample requirements
Serum, heparinised plasma or EDTA plasma. Centrifuge the samples within two hours of collection. If assay is not completed within 8 hours, serum or plasma can be stored at 2–8°C for 48 hours or frozen at –20°C for up to 6 months. Once thawed, do not refreeze.
Maximum turnaround time
24 h
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Triiodothyronine (free)
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printAlternative test name
FT3, Free T3
Purpose and scope
Thyroid stimulating hormone (TSH) stimulates the synthesis, storage, secretion and metabolism of thyroxine (T4) and triiodothyronine (T3). T3 is the major biologically active thyroid hormone. Of the circulating T3, about 80% is formed from peripheral deiodination of thyroxine (T4), and 20% is secreted directly by the thyroid gland.
Free T4 and free T3 regulate normal growth and development, by maintaining body temperature and stimulating calorigenesis. Also, free T4 and free T3 affect all aspects of carbohydrate metabolism, as well as certain areas of lipid and vitamin metabolism. Fetal and neonatal development also require thyroid hormones.
When plasma concentrations of thyroid hormone binding proteins are normal, total T3 concentrations correlate closely with free T3. Total T3 is an unreliable measure of free T3 in the presence of abnormalities in thyroid hormone binding proteins, especially in cases with abnormal thyroxine binding globulin (TBG), or low albumin concentrations.
Measurement of free T3 in clinical trials is done if it is anticipated that an investigational medicinal product (IMP) could affect thyroid function.Method
Two-step competitive enzyme immunoassay
Sample requirements
Serum or plasma (heparin). Samples are stable for 8 h at room temperature, 48 h at 2–8°C, or for 6 months at –20°C.
Maximum turnaround time
24 h
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Triiodothyronine (total)
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printAlternative test name
Total T3, TT3
Purpose and scope
The hypothalamus produces thyrotropin releasing hormone (TRH), which stimulates the synthesis and release of thyroid stimulating hormone (TSH) by the pituitary gland. In turn, TSH binds to receptors in the thyroid gland, resulting in the synthesis, storage, secretion and metabolism of triiodothyronine (T3) and thyroxine (T4).
99% of T3 and T4 in the blood is bound to serum proteins, and is biologically inactive. Free T3 and T4 bind to receptors in target tissues, thereby regulating body temperature, carbohydrate metabolism and some aspects of lipid and vitamin metabolism. T3 is up to 9 times more biologically active than T4. About 80% of T3 is not secreted directly by the thyroid, but is derived by the enzymatic removal of an iodine atom from T4, mainly in the liver.
The clinical importance of total serum T3 measurement is in the diagnosis of thyroid disorders. Serum concentrations of T3 are higher than normal in Grave's disease, and most other types of hyperthyroidism, and are reduced in primary hypothyroid diseases such as Hashimoto's thyroiditis and neonatal hypothyroidism. In clinical trials of new medicines, total T3 serves as a marker of drug effects on thyroid function.Method
Competitive immunoenzymatic assay
Sample requirements
Serum or plasma (heparin). Samples are stable for 8 h at room temperature, and for 24 h at 2–8°C. For longer storage, store at –20°C or colder.
Maximum turnaround time
24 h
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Troponin I
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printAlternative test name
cTnI
Purpose and scope
Troponin protein complex regulates skeletal and cardiac muscle contraction. It inhibits the ATPase activity of the actin-myosin complex in the absence of calcium, thereby preventing muscle contraction. Troponin protein complex consists of 3 subunits: troponin C, troponin T and troponin I. Cardiac Troponin I (cTnI) is found only in cardiac muscle.
CTnI is a biochemical marker of cardiac damage in patients with suspected acute coronary syndromes: it can be detected in a patient's blood 3–6 h after the onset of chest pain, reaching a peak concentration at 12–16 h. The concentration of cTnI may remain elevated for 4–9 days after a myocardial infarction.
In clinical trials of new medicines, cTnI serves as a marker of cardiac muscle damage.Method
Two-step immunoenzymatic ‘sandwich' assay
Sample requirements
Serum. Samples are stable for 2 h at room temperature, and for 24 h at 2–10°C.
Maximum turnaround time
24 h
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Urea
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printPurpose and scope
Urea is the major nitrogen-containing metabolite of protein breakdown in humans. Its serum concentration may be elevated in renal disease, particularly in pre-renal failure, eg dehydration and gastro-intestinal haemorrhage, and decreased in liver failure and malnutrition. In clinical trials of new medicines, urea most often serves as a test of renal function.
Method
Enzymatic rate method
Sample requirements
Fresh, haemolysis-free serum or plasma (heparinised, EDTA or oxalate/fluoride). Centrifuge the samples within two hours of collection. It is stable for 3 days at room temperature, or 5 days at 2–8ºC. The sample can be frozen at –20°C for up to 6 months. Once frozen, do not refreeze.
Maximum turnaround time
24 h
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Uric acid
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printAlternative test name
Urate
Purpose and scope
Uric acid is the end product of the metabolism of purines, adenine and guanine, which are constituents of nucleic acid (DNA and RNA). Adenine is oxidized to hypoxanthine, and then again to xanthine by xanthine oxidase; guanine is oxidized directly to xanthine. Xanthine is oxidized to uric acid by xanthine oxidase. 75% of uric acid is excreted in the urine, the remainder being metabolised by intestinal bacteria.
Elevated levels of uric acid are the cause of gout, and deposition of urate crystals can cause damage elsewhere in the body, eg the kidney. In clinical trials of new medicines, uric acid is measured if the study medicine might affect blood levels.Method
Timed-endpoint method
Sample requirements
Serum, or plasma (EDTA or heparinised). Centrifuge the samples within two hours of collection. It is stable for 3 days at room temperature or 5 days at 2–8ºC. The sample can be frozen at –20°C for up to 6 months. Once thawed, do not refreeze.
Maximum turnaround time
24 h
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Von Willebrand Factor Antigen
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printAlternative test name
VWF:Ag
Purpose and scope
The von Willebrand Factor Antigen (VWF:Ag) is a protein involved in a congenital bleeding disorder – von Willebrand disease (VWD). VWF:Ag binds non-covalently to Factor VIII, and then stabilises it, and protects it against degradation. VWF:Ag is also required for adhesion of platelets to damaged blood vessels.
In congenital VWD, or acquired VWD (due to autoantibodies, or to various disease states), the rate of VWF:Ag synthesis is reduced. In chronic or acute inflammatory disease, or processes involving damage to the vascular endothelium, the concentration of VWF:Ag is greater than normal.
In clinical trials of new medicines, VWF:Ag serves as a marker of effects on blood coagulation. It is also used, in association with Factor VIII assay, as a screening test to identify carriers of haemophilia A.Method
Immuno-turbidimetric
Sample requirements
109 mmol/L buffered sodium citrate plasma with a 9:1 ratio of blood to citrate. Store at –40°C or lower for up to 2 months.
Maximum turnaround time
24 h
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