Sex hormone–binding globulin (SHBG) is a glycoprotein that binds and transports circulating sex steroids, primarily testosterone and estradiol. Less than 2% of biologically active steroid hormones circulate in the free state, with the majority bound to SHBG or albumin. SHBG binds 17-hydroxysteroid hormones with high affinity, whereas albumin binds these hormones with lower affinity.
Although the free hormone fraction was initially considered the only biologically active component, it is now recognized that the albumin-bound fraction is readily dissociable and biologically available to tissues. The sum of free and albumin-bound hormone constitutes the “bioavailable” fraction. Measurement of SHBG is therefore useful for assessing androgen or estrogen status, particularly in cases where clinical features suggest hormone excess or deficiency despite normal total hormone concentrations.
Elevated SHBG concentrations may be observed in individuals with androgen insensitivity, hyperthyroidism, liver cirrhosis, and in patients receiving oral contraceptives or antiepileptic medications. Increased SHBG levels are also characteristic of pregnancy due to estrogen-stimulated hepatic synthesis. Decreased SHBG concentrations are commonly seen in men with hypothyroidism or receiving androgen replacement therapy, and in women with hirsutism, virilization, polycystic ovary syndrome (PCOS), obesity, acromegaly, or elevated androgen levels.
Store/transport at 15–30°C for ≤8 hours; 2–8°C for ≤7 days; freeze at ≤ –20°C if delayed. Avoid repeated freeze–thaw cycles.
Hemolyzed or unseparated specimens.
Enhanced Chemiluminescence
| Population | Reference Interval |
| Adult Males (20–50 years) | 13.3–89.5 nmol/L |
| Adult Females (20–46 years) | 18.2–135.5 nmol/L |
| Postmenopausal Females (47–91 years) | 16.8–125.2 nmol/L |