SHBG is the liver-made carrier protein that locks up testosterone and estradiol in the blood. Its level decides how much hormone is actually free to act, and low SHBG doubles as an early flag for insulin resistance and fatty liver.
Standard range versus optimal range
| Framework | SHBG value | Source |
|---|---|---|
| Adult men, typical reference | about 10-57 nmol/L | Common laboratory range |
| Adult women, typical reference | about 18-144 nmol/L | Common laboratory range |
| Metabolic marker | low values predict type 2 diabetes in cohort studies | Prospective cohort literature |
When it runs high
High SHBG binds more hormone and lowers the free, active share of testosterone and estradiol. Symptoms of hormone deficiency can appear despite normal totals, the classic trap in older men and in hyperthyroid patients.
- Aging, especially in men
- Hyperthyroidism
- Estrogen exposure and pregnancy
- Liver disease
- Caloric restriction and low body weight
- Anticonvulsant medicines
When it runs low
Low SHBG leaves more hormone unbound and is one of the earliest laboratory signs of insulin resistance, often appearing years before glucose rises. In women it unmasks androgen excess, in men it makes total testosterone read falsely low.
- Insulin resistance, obesity and fatty liver, the dominant cause
- Hypothyroidism
- Growth hormone excess
- Glucocorticoids and androgenic progestins
- Genetic variants affecting liver production
The gatekeeper of hormone availability
SHBG is built in the liver, and its production answers directly to metabolic state. Insulin and fat in the liver suppress it, thyroid hormone and estrogen stimulate it. Because SHBG-bound hormone is essentially in storage, the protein acts as a valve between the amount of hormone in blood and the amount tissues feel. Every free hormone calculation flows through this number, which is why no serious interpretation of total testosterone or estradiol skips it.
A stealth metabolic marker
Prospective cohorts show that low SHBG predicts future type 2 diabetes and metabolic syndrome in both sexes, independent of weight. The mechanism runs through liver fat, as de novo lipogenesis from excess carbohydrate pours substrate into the same pathway that suppresses SHBG synthesis. A falling SHBG over serial checks is often the first chemical whisper of insulin resistance, arriving before fasting glucose or even fasting insulin moves.
Moving it in the right direction
Weight loss, improved insulin sensitivity and treatment of fatty liver raise a low SHBG, and the rise confirms the metabolic repair is real. Very low carbohydrate and ketogenic diets lower it further in some people, worth remembering when a free hormone calculation looks odd. Persistent high values deserve a thyroid check, and persistent low values in a lean person warrant a closer look at insulin dynamics.
Related calculators
Related biomarkers Free testosterone · Total testosterone