What does the Sex Hormone-Binding Globulin (SHBG), Serum test measure?

Why is Sex Hormone-Binding Globulin (SHBG), Serum measured?

SHBG is the critical interpretive companion to total testosterone — without SHBG, total testosterone cannot be accurately contextualised as representing actual androgen bioavailability. Elevated SHBG (from ageing, liver disease, hyperthyroidism, OCP, HRT, or caloric restriction) reduces the free and bioavailable testosterone fractions despite normal or even high-normal total testosterone, producing symptomatic androgen deficiency that total testosterone alone would not identify. Conversely, reduced SHBG (from insulin resistance, obesity, exogenous androgens, progestogens, or glucocorticoids) increases free and bioavailable testosterone fractions despite low-normal total testosterone, potentially explaining androgenic signs in women with apparently normal total testosterone. In males, low SHBG alongside normal total testosterone but low free testosterone is a clinically meaningful pattern — particularly in obese, insulin-resistant patients — where the low SHBG reduces the total testosterone threshold at which symptoms of androgen deficiency occur. In females, SHBG is the denominator of the Free Androgen Index (FAI) and is central to diagnosing the metabolic androgen excess of PCOS.

Reference ranges

Standard reference

Male (18+): 16.5–55.9 nmol/L; Female (18+): 17.3–125.0 nmol/L # REVIEWER FLAG: Confirm LabCorp sex-specific and age-stratified reference ranges for SHBG — SHBG rises substantially with age and differs considerably between sexes; the ranges above are approximate LabCorp values. Confirm whether LabCorp provides separate premenopausal and postmenopausal female ranges, and confirm whether age-stratified male ranges are reported.

Functional medicine optimal

Male: 25–50 nmol/L (functional medicine optimal — SHBG below 20 nmol/L in males indicates significant insulin resistance or androgen excess and warrants metabolic assessment; SHBG above 60 nmol/L in younger males warrants thyroid and liver assessment); Female: 40–80 nmol/L (premenopausal optimal for adequate sex steroid buffering capacity without excessive androgen sequestration). # REVIEWER FLAG: SHBG optimal ranges are not standardised in mainstream endocrine guidelines — reviewer to confirm appropriate framing.

Units

nmol/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.