Sex hormone-binding globulin (SHBG) is a glycoprotein that binds to androgen and estrogen sex hormones. Other steroids such as progesterone, cortisol, and other corticosteroids are bound by transcortin.

SHBG is primarily ordered in conjunction with other tests to evaluate androgen levels. In men, the issue of concern is testosterone deficiency, while in women the concern is excess testosterone production. 

A total testosterone may be ordered prior to or along with a SHBG test to evaluate free androgens by calculating the Free Androgen Index (FAI). This equation gives doctors an idea of the quantity of testosterone that is not bound (bioavailable testosterone) to SHBG and is calculated as follows: FAI = Total Testosterone / SHBG.