Sex Hormone-Binding Globulin (SHBG)
Sex hormone-binding globulin (SHBG) is a liver protein that binds testosterone and oestrogen in the blood; it is lowered by high insulin and is a useful marker of insulin resistance.
Plain English
Patient-Friendly Explanation
Sex hormone-binding globulin, or SHBG, is a protein made mainly by the liver that attaches to sex hormones such as testosterone and oestrogen and carries them through the bloodstream. Only the hormone that is not bound - the free portion - can act on the body, so SHBG effectively acts as a control valve on how much hormone is active. Insulin suppresses SHBG production, which is why people with excess weight and insulin resistance often have low SHBG levels, and why SHBG rises when insulin sensitivity improves. Because of this link, SHBG is used both to interpret sex-hormone results correctly and as an indirect marker of metabolic health. Measuring it alongside testosterone is what makes a testosterone result meaningful.
Medical
Clinical Definition
SHBG is synthesised by hepatocytes and its circulating concentration is regulated principally by insulin, which suppresses hepatic SHBG transcription; thyroid hormone raises, and oestrogen and androgen status modulate, its production. Low SHBG is strongly associated with visceral adiposity, hyperinsulinaemia, insulin resistance, non-alcoholic fatty liver disease, metabolic syndrome and incident type 2 diabetes, and in several cohorts it predicts diabetes risk independently of established risk factors. In polycystic ovary syndrome, low SHBG reflects the underlying insulin resistance and amplifies free androgen availability, contributing to hirsutism and ovulatory dysfunction. Because total testosterone measurements are misleading when SHBG is abnormal, free and bioavailable testosterone should be derived from total testosterone plus SHBG and albumin using validated equations (for example Vermeulen). Interpretation caveats include the effect of oral oestrogen, thyroid disease, liver disease, obesity, ageing and some medications.
Key Insight
Why It Matters
A blood test can show a normal total testosterone level yet the patient still has symptoms, because the binding protein changes how much hormone is actually active. That is why we measure SHBG with sex hormones in patients with excess weight, and why we treat the underlying insulin resistance rather than the number alone.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: September 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
