SHBG is a protein that carries the sex hormones (testosterone, estradiol) through the blood and regulates how much of them is free and active. The more SHBG there is, the fewer free hormones, and vice versa.
But SHBG has an unexpected role too: its level is a sensitive marker of metabolism. A low SHBG is closely tied to insulin resistance, obesity and metabolic syndrome.
Reference ranges
The reference range depends on the lab, sex and age; approximately:
| Men | ≈ 13 – 71 nmol/L |
| Women | ≈ 18 – 144 nmol/L |
| Low SHBG | insulin resistance, obesity, hypothyroidism |
| High SHBG | hyperthyroidism, estrogens, liver disease |
What an elevated level means
A high SHBG means that more of the sex hormones are "bound" and less remains in the active free form.
Causes: hyperthyroidism, taking estrogens (including oral contraceptives), liver disease, low weight, older age. In men a high SHBG can mask a deficiency of free testosterone when the total is formally normal.
What a low level means
A low SHBG is an important metabolic signal. It is closely tied to insulin resistance, obesity, metabolic syndrome and fatty liver disease, and in women to PCOS.
Other causes: hypothyroidism, taking androgens and glucocorticoids. With a low SHBG the share of free hormones rises, which is important to account for when assessing androgens.
How the test is done
SHBG is measured in blood from a vein, usually together with the sex hormones. It is used to calculate free and bioavailable testosterone — more accurate measures than total testosterone.
As a metabolic marker, SHBG is assessed in the context of weight, glucose and insulin.
What affects the value
- Insulin resistance and obesity — lower SHBG.
- Estrogens (incl. combined oral contraceptives) — raise it.
- Hyperthyroidism — raises it, hypothyroidism lowers it.
- Liver disease — raises it.
- Androgens and glucocorticoids — lower it.
- Age — in men SHBG rises with age.
Assess insulin resistance
A low SHBG is linked to insulin resistance — assess it from your lab results:
Frequently asked questions
Why is SHBG needed if you have testosterone?
Total testosterone includes the bound, inactive part. SHBG shows how much of the hormone is "bound" and lets you calculate free (active) testosterone. So when there are hormone-related complaints, SHBG is tested together with testosterone or estradiol.
Why is a low SHBG linked to metabolism?
Insulin suppresses SHBG production by the liver, so in insulin resistance and obesity its level falls. A low SHBG is regarded as an early, sensitive marker of metabolic syndrome and the risk of type 2 diabetes.
What does a high SHBG mean?
That more of the sex hormones are bound and less is active. Causes are hyperthyroidism, taking estrogens, liver disease, low weight. In men a high SHBG can hide a deficiency of free testosterone when the total is normal.
Related terms
Sources
- Low SHBG in US adults: prevalence and risk factors. NCBI/PMC
- SHBG and insulin resistance prediction. NCBI/PMC
- MedlinePlus (NIH) — SHBG Blood Test