Specimen Information

Type

Gold, SST

Volume

1.0 ml

Transport Info

Refrigerated
5 day stability

Fasting Required?

False

Clinical Significance

As an aid in the differential diagnosis of hirsutism. Measurement of total testosterone and SHBG provide information of free testosterone and bioavailable testosterone in vivo.
SHBG is a glycoprotein, synthesized in the liver, which binds testosterone and 5-dihydro-testosterone with high affinity and estradiol with somewhat lower affinity. It has a single steroid hormone-binding site, a molecular mass of approximately 80,000 to 100,000 daltons, and consists of two subunits, roughly equal in size. SHBG typically circulates at higher concentrations in women than in men, due to the higher ratio of estrogens to androgens in women. For the same reason, SHBG levels in late pregnancy or after estrogen administration may be especially elevated. Administration of androgens tends to be associated with decreased SHBG levels. Testosterone circulates primarily protein-bound, principally to SHBG, but also to albumin and cortisol-binding globulin. Since variations in the carrier protein levels may affect the concentration of testosterone in circulation, SHBG levels are commonly measured as a supplement to total testosterone determinations. The free androgen index (FAI), calculated as the ratio of total testosterone to SHBG, has proved to be a useful indicator of abnormal androgen status in conditions such as hirsutism.