SHBG (Sex hormone-binding globulin)

SHBG is a liver-synthesised glycoprotein that binds approximately 98% of circulating testosterone and 30-60% of estradiol with high affinity, regulating the bioavailable hormone fraction. It is measured by automated immunoassay (electrochemiluminescence, chemiluminescence) with platform-dependent reference ranges of roughly 10-80 nmol/L in adult men and 20-130 nmol/L in non-pregnant women; mass spectrometry serves as criterion method. SHBG falls with insulin resistance, obesity, type 2 diabetes, exogenous androgens, hypothyroidism, glucocorticoids, growth hormone, and advanced liver disease, and rises with estrogens, oral contraceptives, hyperthyroidism, anorexia, and ageing in men. Its main clinical use is correcting total testosterone interpretation by calculating free or bioavailable testosterone (Vermeulen formula). Inter-assay variability is large enough to alter clinical classification, so serial measurements should use the same platform.