Sex Hormone Binding Globulin (SHBG) is a glycoprotein produced primarily by the liver that binds and transports sex hormones in the bloodstream. SHBG levels directly influence the bioavailability of testosterone and estradiol, making it essential for accurate assessment of hormonal status and calculation of free hormone levels. SHBG binds with high affinity to testosterone and dihydrotestosterone, and with lower affinity to estradiol, effectively regulating the fraction of these hormones available to tissues. Hepatic SHBG production is upregulated by estrogens and thyroid hormones while being suppressed by androgens and insulin, creating a complex regulatory system that reflects metabolic and hormonal balance.
Sex hormone-binding globulin (SHBG) is a glycoprotein produced by the liver that binds testosterone and estradiol with high affinity, regulating their bioavailability. Only the unbound (free) fraction of these hormones is biologically active at target tissues. SHBG is therefore essential for accurate interpretation of total testosterone and estradiol levels.
High SHBG reduces bioavailable testosterone, potentially causing symptoms of androgen deficiency despite normal total testosterone. Low SHBG increases free hormone availability and is associated with insulin resistance, metabolic syndrome, type 2 diabetes, and polycystic ovary syndrome (PCOS). Thyroid hormone excess raises SHBG; hypothyroidism lowers it.
SHBG is influenced by insulin, thyroid status, body composition, and dietary patterns. Low-carbohydrate diets and caloric surplus tend to lower SHBG, while caloric restriction and aging increase it. Because total testosterone alone does not reflect bioavailable testosterone, concurrent SHBG measurement is necessary for meaningful hormonal assessment.
Turnaround Time
3 days (up to 12 days)
Fasting Required
No
Method
Immunoassay (ECLIA)
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