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TESTOSTERONE, F EQLIB+T LC/MS
Test Code70038
CPT Codes
84402; 84403
Preferred Specimen
"Serum
2.5 mL
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2.5 mL
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Minimum Volume
"1 mL (Note: This volume does not allow for repeat testing.)
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Instructions
"If a red-top tube is used, transfer separated serum to a plastic transport tube.
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Transport Container
"Red-top tube or gel-barrier tube
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Transport Temperature
Refrigerated
Specimen Stability
Refrigerated
Methodology
"Free: equilibrium ultrafiltration; total: liquid chromatography/tandem mass spectrometry (LC/MS-MS) "
Clinical Significance
"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)
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.
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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.
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