SHBG (Sex Hormone Binding Globulin) is a blood test that measures shbg (sex hormone binding globulin) levels in the blood. Normal range: Men: 15 - 50 nmol/L · Women: 30 - 90 nmol/L (Australian adult reference range; rises with age, lowered by insulin resistance and androgens). It is commonly used to sHBG is essential for correctly interpreting total testosterone results. A man with normal total testosterone but low SH...
What is SHBG (Sex Hormone Binding Globulin)?
SHBG (Sex Hormone Binding Globulin) is a glycoprotein produced by the liver that binds tightly to testosterone, dihydrotestosterone (DHT) and oestradiol. The portion of testosterone bound to SHBG is biologically inactive, so SHBG levels directly determine how much "free" (bioavailable) testosterone reaches tissues. Insulin and androgens lower SHBG; oestrogen, thyroid hormone and ageing raise it.
Why is it measured?
SHBG is essential for correctly interpreting total testosterone results. A man with normal total testosterone but low SHBG can still be functionally hypogonadal because his free testosterone is suppressed - a pattern common in obesity, type 2 diabetes and metabolic syndrome. In women, low SHBG amplifies free testosterone and is a hallmark of PCOS (used in the Free Androgen Index calculation: FAI = total T / SHBG x 100). On TRT, SHBG often drops, which is why "free testosterone" or "calculated free T" is monitored alongside total T.
Normal Reference Range
Men: 15 - 50 nmol/L · Women: 30 - 90 nmol/L (Australian adult reference range; rises with age, lowered by insulin resistance and androgens)
Note: Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation.
What Causes High SHBG?
High SHBG binds up more sex hormone, lowering free (active) testosterone and oestrogen. Causes include ageing, an overactive thyroid (hyperthyroidism), liver disease and cirrhosis, oestrogen exposure (the combined pill, pregnancy, hormone therapy), anorexia and significant calorie restriction, and some anticonvulsant medications. In men, high SHBG can produce symptoms of low testosterone even when total testosterone looks normal, because free testosterone is reduced.
What Causes Low SHBG?
Low SHBG raises free testosterone and is a hallmark of insulin resistance. The common causes are obesity, type 2 diabetes and metabolic syndrome, polycystic ovary syndrome (where low SHBG amplifies androgen effects), an underactive thyroid, Cushing's syndrome, acromegaly, and the use of testosterone or anabolic steroids. In women, low SHBG contributes to acne, excess hair growth and the PCOS picture.
How Often Should SHBG Be Tested?
SHBG is measured together with total testosterone so that free or calculated free testosterone can be worked out — the result that best reflects active hormone. It is checked when investigating low testosterone in men, androgen excess or PCOS in women, and is rechecked when starting or adjusting testosterone replacement, since SHBG often falls on treatment.
Related Blood Markers
SHBG is interpreted with total testosterone (to derive free testosterone and, in women, the free androgen index), oestradiol, and albumin. Thyroid function and markers of insulin resistance (glucose, HbA1c) help explain an abnormal level.
Key Facts
- •Category: Hormone Health
- •Unit of Measurement: nmol/L
- •Test Code: SHBG
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