Sex Hormone Binding Globulin (SHBG) Test
Sex hormone binding globulin is a hepatic glycoprotein that binds circulating sex steroids and determines their bioavailability, binding dihydrotestosterone and testosterone with high affinity and oestradiol less avidly. It is measured principally to interpret total testosterone and to calculate free and bioavailable testosterone, since total testosterone becomes unreliable whenever binding…
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Biomarkers
Blood (serum)
Sample
2–4 business days
Turnaround
No — fasting is not specifically required, though SHBG is commonly collected with a morning fasting testosterone, in which case the testosterone protocol governs
Fasting
What is the SHBG test?
The SHBG Test measures sex hormone binding globulin, the hepatic glycoprotein that binds circulating sex steroids and governs how much of them is available to tissues. It binds dihydrotestosterone and testosterone with high affinity and oestradiol less avidly, so changes in SHBG alter the balance of bioavailable androgen and oestrogen without any change in gonadal output. It is ordered principally to interpret total testosterone correctly and to calculate free and bioavailable testosterone, and secondarily in the assessment of hyperandrogenism in women. The clinical case for measuring SHBG rests on a straightforward problem: total testosterone measures bound and free hormone together, so it becomes an unreliable index of androgen status whenever binding capacity is abnormal. This is not an edge case. SHBG is suppressed by insulin and androgens and raised by oestrogen and thyroid hormone, so it falls in obesity, insulin resistance, type 2 diabetes, and hypothyroidism, and rises with ageing, hyperthyroidism, oestrogen therapy, pregnancy, and hepatic disease — collectively describing a large proportion of patients in whom testosterone is measured. A man with obesity may have a low total testosterone with preserved free testosterone and no true androgen deficiency, while an older man with a high SHBG may have a reassuring total testosterone alongside genuinely inadequate bioavailable hormone. Measuring SHBG alongside total testosterone and albumin allows free testosterone to be calculated, which is the practical route to a reliable free testosterone value given that direct analogue immunoassays for free testosterone perform poorly. In women, a low SHBG raises free testosterone and is a recognised contributor to the clinical hyperandrogenism of polycystic ovary syndrome, so SHBG helps explain androgenic symptoms in the presence of an unremarkable total testosterone. SHBG has also attracted attention as an independent marker of insulin resistance and cardiometabolic risk; that association is consistent in observational data but has not translated into a validated clinical target, and it should inform interpretation rather than drive management.
What does the SHBG test measure?
Sex hormone binding globulin is a homodimeric glycoprotein synthesised principally by the liver, which binds circulating sex steroids with high affinity and thereby regulates their bioavailability. It binds dihydrotestosterone most avidly, then testosterone, and oestradiol with roughly a third of testosterone's affinity. In men, approximately 44–65% of circulating testosterone is bound to SHBG, a similar proportion is loosely bound to albumin, and only 1–2% circulates free. Only the free and albumin-bound fractions are considered bioavailable, since the SHBG-bound fraction is not readily released to tissues. Hepatic SHBG synthesis is upregulated by oestrogen and thyroid hormone and suppressed by insulin and androgens, which is why SHBG tracks so closely with metabolic and endocrine state.
SHBG is rarely informative in isolation and derives almost all of its clinical value as a denominator: it is measured to interpret total testosterone correctly and to calculate free and bioavailable testosterone. Total testosterone becomes misleading whenever SHBG is abnormal — a low SHBG in obesity or insulin resistance depresses total testosterone while free testosterone may be preserved, and a high SHBG in ageing, hyperthyroidism, or oestrogen therapy elevates total testosterone while bioavailable hormone may be inadequate. SHBG is also increasingly described as an independent marker of insulin resistance and metabolic risk, a relationship that is consistent in observational data but not yet established as a guideline-actionable clinical target.
Why is the SHBG test ordered?
- Interpretation of total testosterone in men where an abnormal binding capacity is likely — obesity, insulin resistance, type 2 diabetes, ageing, thyroid disease, or hepatic disease
- Calculation of free and bioavailable testosterone from total testosterone, SHBG, and albumin, where a reliable free testosterone value is required
- Investigation of suspected male hypogonadism where total testosterone is borderline or discordant with the clinical picture
- Assessment of hyperandrogenism in women, including suspected polycystic ovary syndrome, where a low SHBG raises free testosterone despite an unremarkable total testosterone
- Evaluation of androgenic or oestrogenic symptoms in patients on oestrogen therapy, oral contraceptives, or thyroid hormone, all of which alter SHBG substantially
- Assessment of patients on androgen or anabolic steroid therapy, where suppressed SHBG alters the relationship between total and free testosterone
- Investigation of discordance between total testosterone and the clinical picture, where binding capacity is the likely explanation
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No — fasting is not specifically required, though SHBG is commonly collected with a morning fasting testosterone, in which case the testosterone protocol governs
Collection method
Venipuncture at patient service centre
Turnaround
2–4 business days
Collection notes
Where SHBG is being used to calculate free testosterone, collect alongside total testosterone and albumin on the same specimen, following the early-morning fasting protocol required for testosterone. Document oestrogen therapy or oral contraceptives, androgen or anabolic steroid use, thyroid status and thyroid hormone therapy, glucocorticoids, anticonvulsants, pregnancy, and known hepatic disease. Use the same laboratory, assay, and calculation method for serial monitoring.
Specimen requirements
Minimum 0.5 mL serum. Separate serum from cells per Quest protocol. Specimen stable refrigerated; follow Quest transport guidelines.
What can affect SHBG results?
Oestrogen strongly upregulates hepatic SHBG synthesis, and oral preparations do so more than transdermal because of first-pass hepatic exposure. SHBG rises markedly in pregnancy, raising total testosterone while free testosterone may be unchanged.
Insulin suppresses hepatic SHBG synthesis, so SHBG falls as insulin resistance increases. This lowers total testosterone in men while free testosterone may be preserved, and raises free testosterone in women, contributing to clinical hyperandrogenism.
Thyroid hormone stimulates hepatic SHBG synthesis, so SHBG rises in hyperthyroidism and falls in hypothyroidism. Thyroid status should be established before attributing an abnormal SHBG or a discordant testosterone to gonadal or metabolic causes.
Exogenous androgens suppress hepatic SHBG synthesis, sometimes markedly with oral or supraphysiological preparations, altering the relationship between total and free testosterone and complicating interpretation in treated patients.
SHBG rises with advancing age and in chronic liver disease including cirrhosis, so an older or hepatically impaired patient may have a reassuring total testosterone alongside inadequate bioavailable hormone.
SHBG assays are not fully harmonised between manufacturers, and calculated free testosterone additionally depends on which equation is used, since the commonly applied formulae do not yield identical values. Serial monitoring should use the same laboratory, assay, and calculation method.
What do SHBG results mean?
Elevated
A raised SHBG lowers the bioavailable fraction of testosterone, so total testosterone overestimates androgen status. Common causes are ageing, hyperthyroidism, oestrogen therapy or oral contraceptives, pregnancy, hepatic disease including cirrhosis, anorexia nervosa, and some anticonvulsants. In men, a high SHBG with an apparently normal total testosterone may conceal genuinely low free testosterone, so free testosterone should be calculated before excluding hypogonadism.
Normal
A normal SHBG supports the reliability of total testosterone as an index of androgen status in that patient. It does not exclude gonadal dysfunction, which is assessed on total and calculated free testosterone alongside LH, FSH, and the clinical picture.
Reduced
A low SHBG raises the bioavailable fraction, so total testosterone underestimates androgen status. Common causes are obesity, insulin resistance, type 2 diabetes, metabolic syndrome, hypothyroidism, androgen or anabolic steroid use, glucocorticoids, and acromegaly. In men, a low SHBG with a low total testosterone may reflect preserved free testosterone rather than true androgen deficiency. In women, a low SHBG contributes to clinical hyperandrogenism and is characteristic of polycystic ovary syndrome even where total testosterone is unremarkable.
Note: SHBG is rarely interpretable alone and is measured to contextualise testosterone rather than as a standalone marker. It is strongly influenced by metabolic and endocrine state, so thyroid status, insulin resistance, hepatic function, and oestrogen or androgen exposure should be established before drawing conclusions. Assays are not fully harmonised and calculated free testosterone varies with the equation used, so serial monitoring requires the same laboratory, assay, and calculation. Its association with insulin resistance and cardiometabolic risk is observationally consistent but has not been established as a validated clinical target.
Frequently asked questions
It measures sex hormone binding globulin, the hepatic glycoprotein that binds circulating sex steroids and governs how much is available to tissues. It binds dihydrotestosterone and testosterone with high affinity and oestradiol less avidly.
How to access the SHBG test
The SHBG reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: July 16, 2026
Last reviewed: July 16, 2026
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. (2018)
- Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. (1999)
- Hammond GL. Diverse roles for sex hormone-binding globulin in reproduction. Biol Reprod. (2011)
- Ding EL, et al. Sex hormone-binding globulin and risk of type 2 diabetes in women and men. N Engl J Med. (2009)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.