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Testosterone, Free, Equilibrium Ultrafiltration With Total Testosterone, LC/MS-MS
Evaluate hirsutism and masculinization in women; evaluate testicular function in clinical states in which the testosterone-binding proteins may be altered (obesity, cirrhosis, thyroid disorders)
This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.
Free: equilibrium ultrafiltration; total: liquid chromatography/tandem mass spectrometry (LC/MS-MS)
The concentration of free testosterone is very low, typically <2% of the total testosterone concentration. In most men and women, >50% of total circulating testosterone is bound to sex hormone-binding globulin (SHBG) and most of the rest is bound to albumin.1 Routinely available assay methods used to measure total testosterone are not sensitive enough to quantitate accurately the free testosterone fraction directly. Free testosterone is estimated in this profile by an indirect method, equilibrium ultrafiltration. Tritiated testosterone is added to the sample and allowed to come to equilibrium with testosterone in the serum at physiological temperature.2,3 The amount of the added radiolabeled testosterone must be low enough to ensure that the addition will not significantly increase the total testosterone concentration. Once equilibrium is achieved, the free testosterone is separated from the bound testosterone by filtration through a membrane by centrifugal ultrafiltration.4 The radioactivity of the protein-free ultrafiltrate is measured and used to calculate the percent free testosterone. The concentration of free testosterone is then calculated by multiplying the percent free testosterone by the total testosterone concentration.
1 mL (Note: This volume does not allow for repeat testing.)
Red-top tube or gel-barrier tube
Serum should be transferred from cells within one hour of collection and transferred to a plastic transport tube.
Causes for Rejection
Gross lipemia; recently administered isotopes; plasma specimen; improper labeling; specimen drawn in citrate or ACD tube
State patient's age and sex on the test request form.
- 1. Wheeler MJ. The determination of bioavailable testosterone. Ann Clin Biochem. 1995; 32(Pt 4):345-357 (review). 7486793
- 2. Klee GG, Heser DW. Techniques to measure testosterone in the elderly. Mayo Clin Proc. 2000; 75(Suppl):S19-S25. 10959211
- 3. Gronowski AM, Landau-Levine M. Reproductive endocrine function. In: Burtis CA, Ashwood ER, eds. Tietz Textbook of Clinical Chemistry. 3rd ed. Philadelphia, Pa: WB Saunders Co; 1999:1601-1641.
- 4. Vlahos I, MacMahon W, Sgoutas D. An improved ultrafiltration method for determining free testosterone in serum. Clin Chem. 1982; 28(11):2286-2291. 7127776
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|070038||Testosterone, F Eqlib+T LC/MS||070036||Testosterone, Total, LC/MS||ng/dL||2986-8|
|070038||Testosterone, F Eqlib+T LC/MS||070039||Testosterone, Free||ng/dL||2991-8|
|070038||Testosterone, F Eqlib+T LC/MS||080770||% Free Testosterone||%||15432-8|