SHBG
Sex hormone-binding globulin regulates the free fraction of testosterone and estradiol
Also known as
Definition
Sex hormone-binding globulin (SHBG) is a transport protein produced in the liver that binds testosterone (~60%) and estradiol (~37%) with high affinity. Only hormone not bound to SHBG is biologically active: free testosterone/estradiol (2–3%) plus the weakly albumin-bound fraction (together = bioavailable). SHBG is therefore the primary regulator of hormone availability and varies substantially with insulin levels, liver health, and age.
| Parameter | Value |
|---|---|
| Unit | nmol/l |
| Reference Range | Men: 13–71 nmol/l | Women (premenopausal): 26–110 nmol/l | Women (postmenopausal): 15–80 nmol/l |
Agree on your personal target range with your doctor.
↓ What a low value means
Low SHBG (< 13 nmol/l men, < 26 nmol/l premenopausal women) is a strong marker of insulin resistance, metabolic syndrome, and visceral adiposity. Associated with increased type 2 diabetes and cardiovascular risk. In men: paradoxically often elevated free testosterone fraction, but increased metabolic risk.
↑ What a high value means
High SHBG reduces free hormone availability. Causes: liver cirrhosis, hyperthyroidism, anorexia, estrogen use (oral contraceptives, HRT), advanced age. In men: hypogonadism symptoms despite normal total testosterone. In women: possible androgen deficiency despite normal total testosterone. Low-carb and calorie-restrictive diets raise SHBG.
✓ What can influence this value
The SHBG value is influenced by insulin levels, body weight, liver and thyroid function, age, and estrogen intake. Insulin resistance and visceral obesity are associated with lower SHBG; hyperthyroidism, liver cirrhosis, estrogen intake, and low-carb and calorie-restrictive diets can raise the value. Boron and zinc have been studied as possible influencing factors on SHBG. The assessment is made by the treating doctor.
When to test
Usually measured together with total testosterone and estradiol. With suspected hyperandrogenism (PCOS), hypogonadism diagnostics, fertility concerns, or when total testosterone is normal but symptoms are present.
Frequently asked questions
Why can a man have normal testosterone values and still show hypogonadism symptoms? +
Because total testosterone measures all fractions — including the inactive SHBG-bound testosterone (~60%). When SHBG is high (e.g., with liver problems, aging, or hyperthyroidism), free (active) testosterone can be low even if total testosterone appears normal. Measuring SHBG at the same time allows free testosterone to be calculated.
Does the birth control pill raise SHBG? +
Yes. Estrogen-containing oral contraceptives significantly raise SHBG (often 3–4-fold), which strongly reduces the free testosterone fraction. Some women report persistently low libido and emotional blunting. In some cases, SHBG normalizes only slowly after stopping the pill (months).
What is the Free Androgen Index (FAI) and what is it used for? +
FAI = total testosterone × 100 / SHBG. In women it is useful for assessing androgen excess (PCOS diagnostics): FAI > 5 in women is considered elevated. In men, the direct free testosterone calculation (Vermeulen formula) is more precise than the FAI.
SHBG
Sources
- Hammond GL (2011) Diverse roles for sex hormone-binding globulin in reproduction. Biol Reprod.
- Bhasin S et al. (2011) Reference ranges for testosterone in men generated using liquid chromatography tandem mass spectrometry in a community-based sample of healthy nonobese young men in the Framingham Heart Study. J Clin Endocrinol Metab.
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.