Sex Hormone Binding Globulin (SHBG)
Sex hormone binding globulin is produced by the liver and binds testosterone, estradiol, and other sex steroids in blood. Only the unbound ('free') fraction is biologically active. SHBG changes the balance of free vs. total hormone — high SHBG lowers bioavailable hormone even when total levels are normal. SHBG is useful in evaluating PCOS, hirsutism, male hypogonadism, and in interpreting testosterone and estrogen results.
Reference Ranges
Male
18 – 54
nmol/L
Female
32 – 128
nmol/L
Child
Consult pediatrician
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Low SHBG is seen in insulin resistance, type 2 diabetes, metabolic syndrome, obesity, PCOS, hypothyroidism, and nephrotic syndrome. Low SHBG increases the free fraction of testosterone, which can worsen symptoms of hyperandrogenism in PCOS. Chronic low SHBG independently predicts future development of type 2 diabetes.
What High Levels Mean
High SHBG is seen in hyperthyroidism, oral estrogen (contraceptives, HRT), anorexia, liver disease, and some medications (anticonvulsants, tamoxifen). High SHBG reduces free testosterone even when total testosterone is normal — a common cause of hypogonadal symptoms in older men on oral estrogens or with liver disease.
Frequently Asked Questions
Why measure SHBG when testosterone is already tested?
Total testosterone includes both bound and free forms. When SHBG is abnormal (common in obesity, diabetes, hyperthyroidism, estrogen use), total testosterone can be misleading. Measuring SHBG allows calculation of free or bioavailable testosterone, which better reflects androgen activity. This is standard in male hypogonadism workup and PCOS evaluation.
Is low SHBG a warning sign?
Yes — chronically low SHBG is an independent predictor of metabolic syndrome and type 2 diabetes, even before glucose becomes abnormal. It reflects insulin resistance at the level of the liver. Lifestyle changes (weight loss, exercise, reduced refined carbohydrates) that improve insulin sensitivity also raise SHBG toward normal.
Does oral contraceptive use affect SHBG?
Yes. Oral estrogen dramatically increases SHBG (often 2–3 fold), which lowers free testosterone. Many women on combined oral contraceptives experience reduced libido and sometimes vulvar dryness because of this. It usually reverses within weeks to months after stopping. Transdermal and intrauterine contraceptives affect SHBG much less.
Related Hormones tests
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Calculated index that estimates insulin resistance.
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mIU/mLHormonesTotal Testosterone
Total blood level of the main male sex hormone.
ng/dLThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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