Sex hormone binding globulin (SHBG) is a glycoprotein of about 80-100 kDa; it has a high affinity for 17 beta-hydroxysteroid hormones such as testosterone and estradiol. SHBG concentration in plasma is regulated by, amongst other things, androgen/estrogen balance, thyroid hormones, insulin and dietary factors. It is the most important transport protein for estrogens and androgens in peripheral blood. SHBG concentration is a major factor regulating their distribution between the protein-bound and free states. Plasma SHBG concentrations are affected by a number of different diseases, high values being found in hyperthyroidism, hypogonadism, androgen insensitivity and hepatic cirrhosis in men. Low concentrations are found in myxoedema, hyperprolactinaemia and syndromes of excessive androgen activity. Measurement of SHBG is useful in the evaluation of mild disorders of androgen metabolism and enables identification of those women with hirsutism who are more likely to respond to estrogen therapy. The ratio of testosterone to SHBG is also known as the Free Androgen Index (FAI) or the Free Testosterone Index (FTI). This ratio correlates well
with both measured and calculated values of free testosterone and helps to discriminate subjects with excessive androgen activity from normal individuals.
Manufacturer’s Reagent package insert Architect SHBG, February 2018, Abbott GmbH & Co. KG, Max-Planck-Ring 2, 65205 Wiesbaden, Germany.