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Testosterone Free, Profile II
- Free Testosterone by Vermeulin Equation
- Free Testosterone, Calculated
Albumin; free testosterone, calculated; sex hormone binding globulin; testosterone by LC-MS
Free testosterone is the concentration of unbound testosterone in serum.1 The majority (approximately 60% to 90%) of serum total testosterone is associated with sex hormone binding globulin (SHBG); this fraction is tightly bound and biologically unavailable to its target tissues. The remaining bioavailable testosterone is mostly bound to albumin, with only a small fraction (approximately 0.5% to 2%) circulating in the free form.1,2 Free testosterone is the form of testosterone that can diffuse into the tissues and act on receptors and is considered the active fraction by many physicians.1,3,4 Free testosterone assessment is recommended as a primary or secondary measure of androgen activity in men2,5-11 and women.12-16 The equilibrium dialysis or ultrafiltration methods are recommended, however they are relatively difficult and expensive to perform. All of these methods are currently available from LabCorp.
The primary screening test for the diagnosis of hypoandrogenism in men is the measurement of total testosterone in serum in a morning sample.2,5-11 Low concentrations of testosterone in serum should be confirmed by repeat measurement, preferably using liquid chromatography/mass spectrometry.6,7,10 Determination of free testosterone can be of value in men with borderline total testosterone because alterations in SHBG levels can markedly affect the concentration of biologically available free testosterone.2,17-20 Factors and conditions that tend to increase SHBG concentrations in men include aging, hyperthyroidism, estrogens, HIV disease, anticonvulsant therapy, and liver disease.2 Factors and conditions that tend to decrease SHBG concentrations in men include obesity, diabetes mellitus, hypothyroidism, glucocorticoid therapy, androgenic steroid therapy, nephrotic syndrome and acromegaly.2
The binding affinities between testosterone, SHBG and albumin have been measured experimentally, and it has been shown that if the concentrations of serum total testosterone, SHBG, and albumin are measured, the corresponding concentration of free testosterone can be accurately estimated according to equilibrium kinetics.21 The widely accepted method of calculation of serum free testosterone is based upon a 1999 paper by Vermeulen.21 The authors derived the equation based upon the law of mass action. Using the known association constants between testosterone, SHBG, and albumin, they calculated the theoretically predicted serum free testosterone concentrations. This method demonstrated substantial agreement with equilibrium dialysis measured concentrations when testosterone, SHBG and albumin are measured using reliable assays.
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This test was developed, and its performance characteristics determined, by LabCorp. It has not been cleared or approved by the US Food and Drug Administration (FDA).
Testosterone: Liquid chromatography/tandem mass spectrometry (LC/MS-MS)
SHBG: Electrochemiluminescence immunoassay (ECLIA)
0 to 1 y
2 to 5 y
6 to 7 y
18 to 30 y
31 to 40 y
41 to 50 y
51 to 60 y
61 to 70 y
71 to 80 y
81 to 100 y
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.
to a plastic transport tube.
Causes for Rejection
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This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|070130||Testosterone Free, Profile II||001081||Albumin||g/dL||1751-7|
|070130||Testosterone Free, Profile II||070036||Testosterone, Total, LC/MS||ng/dL||2986-8|
|070130||Testosterone Free, Profile II||082016||Sex Horm Binding Glob, Serum||nmol/L||13967-5|
|070130||Testosterone Free, Profile II||004230||Testost., Free, Calc||pg/mL||2991-8|