Sex hormone binding globulin (SHBG) is a protein with a mol wt 90 kDa containing two subunits. SHBG transports the sex steroids testosterone, DHT and estradiol in the blood. Serum levels are increased during pregnancy, in women taking estrogens and in men over the age of 50. Levels are reduced after menopause and in response to treatment with androgens or corticosteroids. Diagnostic uses include polycystic ovary disease and tests for liver and thyroid function.