What this test measures
Sex Hormone Binding Globulin (SHBG) is a liver-produced glycoprotein that tightly binds testosterone and oestradiol, regulating their bioavailability. Only the unbound (free) fraction is biologically active. SHBG is therefore a "modulator" — the same total testosterone can mean very different things at different SHBG levels.
SHBG levels are influenced by many factors: obesity, type 2 diabetes and insulin resistance lower SHBG; ageing, hyperthyroidism, oestrogen pills, liver disease and anorexia raise it.
Why it matters
SHBG is the partner test to total testosterone when interpreting reproductive and androgen status. In an obese diabetic man with low SHBG, a "borderline" total testosterone may hide a normal free testosterone (so no hypogonadism). In an older man with high SHBG, a "normal" total testosterone may hide a truly low free testosterone (so real hypogonadism). The Endocrine Society explicitly recommends calculating free testosterone from total + SHBG + albumin in these settings.
In women with PCOS and hirsutism, SHBG is suppressed by hyperinsulinaemia — leading to higher free testosterone even when total testosterone looks normal. A low SHBG in a PCOS workup supports a biochemical hyperandrogenism diagnosis. SHBG is also part of insulin-resistance research and the workup of hepatic and thyroid disorders.
How to prepare
No fasting required. Morning sample preferred for paired interpretation with testosterone. Stop biotin for 48–72 hours. Mention any hormonal medications — oestrogen pills, HRT, anabolic steroids and antiepileptics all change SHBG.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Sex Hormone Binding Globulin (nmol/L)[1][2] | Adult male: 18.3 – 54.1 · Adult female (non-pregnant, non-pill): 32.4 – 128 (assay-dependent) | Low SHBG is seen in obesity, type 2 diabetes, metabolic syndrome, PCOS, hypothyroidism, Cushing's syndrome, anabolic steroid use, and rarely in genetic SHBG variants. Often makes total testosterone look misleadingly low in men. | High SHBG is seen in ageing, hyperthyroidism, oestrogen therapy / pregnancy, liver disease (cirrhosis), anorexia, anti-epileptic drugs (phenytoin, carbamazepine), and HIV. Often makes total testosterone look misleadingly normal in older men who actually have low free testosterone. |
SHBG — interpretation in common scenarios
| Patient | SHBG | Total T | Free T | Interpretation |
|---|---|---|---|---|
| Obese diabetic man | Low | Borderline low | Often normal | Low SHBG masking — recheck free T |
| Older man on no meds | High | Normal | Often low | High SHBG masking — recheck free T |
| Woman with PCOS | Low | Normal | Raised | Biochemical hyperandrogenism |
| Woman on oestrogen pill | High | Raised total | Normal | Pill effect — no true androgen problem |
| Hyperthyroid | High | Variable | Variable | Treat thyroid first, recheck |
| Anabolic steroid use | Very low | Often suppressed (endogenous) | Very high (exogenous) | Suspect exogenous androgens |
Frequently asked questions
Why is SHBG ordered with testosterone?
Because SHBG changes substantially with obesity, ageing, diabetes and thyroid disease — and the same total testosterone can mean opposite things at low vs. high SHBG. Measuring both lets the lab calculate the bioavailable / free fraction that actually drives symptoms.
My SHBG is low — should I be worried?
On its own, no. Low SHBG is a marker of insulin resistance and metabolic syndrome — common in Indians — and an early signal that lifestyle change would help. It is not a disease by itself.
I am a woman with PCOS — what does my SHBG look like?
Almost always low. Insulin resistance in PCOS suppresses hepatic SHBG production, which raises free testosterone even when total testosterone is borderline. A low SHBG in a PCOS workup is part of the typical biochemistry.
How do oral contraceptive pills change SHBG?
Combined OCPs raise SHBG substantially — by binding more testosterone, they reduce free testosterone, which is why they help acne and hirsutism. Total testosterone may look unchanged or slightly higher.
Do I need to fast for SHBG?
No fasting is required. Sample any time of day, though a morning draw paired with testosterone is preferred.
Can I raise my SHBG with lifestyle?
Yes — meaningful weight loss, reducing insulin resistance and getting thyroid status optimal all raise SHBG by 20–50%. In obese men this can substantially improve free testosterone.
My free testosterone was calculated, not measured — is that accurate?
Calculated free testosterone using total T, SHBG and albumin (Vermeulen formula) is the Endocrine Society-endorsed practical approach and is considered accurate enough for clinical decisions. Measured equilibrium-dialysis free T is the gold standard but rarely available outside reference labs.
Related Hormones / Endocrine tests
Tests commonly ordered alongside SEX HORMONE BINDING GLOBULIN (SHBG), or that help interpret an unexpected result.
Sources & references
- Endocrine Society — Testosterone Therapy in Men with Hypogonadism · accessed 2026-05-30T00:00:00.000Z
- Endocrine Society — Hirsutism in Premenopausal Women · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — SHBG Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Sex Hormone Binding Globulin · accessed 2026-05-30T00:00:00.000Z
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