Testosterone, Free, Equilibrium Ultrafiltration with Total Testosterone, LC/MS-MS LabCorp

This test aids in the evaluation of testicular function in clinical states in which the testosterone-binding proteins may be altered (obesity, cirrhosis, thyroid disorders). It may also be used to evaluate hirsutism and masculinization in women. Concentrations of free testosterone is typically very low (typically >2% of the total testosterone concentration. In most men, >50% of total circulating testosterone is bound to sex hormone-binding globulin (SHBG) and most of the remainder is bound to albumin. Routine assay lab methods used to measure total testosterone are not sensitive enough to quantitate the free testosterone fraction accurately and directly. Free testosterone is estimated in this profile by an indirect method, which is equilibrium ultrafiltration. Tritiated testosterone is added to the sample and allowed to come to equilibrium with testosterone into he serum at physiological temperature. 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. The radioactivity of the protein-free ultrafiltrate is measured an dosed to calculate the percentage of free testosterone. The concentration of free testosterone is then calculated by multiplying the percentage of free testosterone by the total testosterone concentration.