SHBG Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is SHBG?

Sex hormone-binding globulin (SHBG) is a glycoprotein produced primarily by the liver that binds to sex hormones - testosterone, dihydrotestosterone (DHT), and oestradiol - in the bloodstream. By binding these hormones, SHBG controls how much is "free" (unbound) and biologically active.

Approximately 60–70% of testosterone in men and 80–90% in women is bound to SHBG. Only the unbound fraction can enter cells and exert effects. This means SHBG effectively acts as a thermostat for sex hormone activity: high SHBG reduces the biological impact of sex hormones, while low SHBG increases it.

SHBG production is influenced by multiple factors including oestrogen (increases SHBG), insulin (decreases SHBG), thyroid hormones (increases SHBG), and androgens (decrease SHBG). Understanding SHBG is essential for interpreting total testosterone results in both sexes.

Why Is SHBG Tested?

• Interpreting testosterone results - a normal total testosterone with abnormal SHBG can indicate androgen excess or deficiency
• PCOS assessment - low SHBG is common in PCOS, increasing bioavailable androgens
• Male hypogonadism - high SHBG can cause symptoms of low testosterone despite normal total levels
• Calculating free androgen index (FAI) - FAI = (total testosterone ÷ SHBG) × 100
• Metabolic health - low SHBG is associated with insulin resistance, metabolic syndrome, and type 2 diabetes
• Liver disease - liver dysfunction alters SHBG production

Normal Ranges

What Do High SHBG Levels Mean?

• Hyperthyroidism - excess thyroid hormones stimulate SHBG production
• Oestrogen therapy - oral contraceptives and HRT significantly raise SHBG
• Pregnancy - oestrogen levels drive SHBG up 5–10 fold
• Liver disease, cirrhosis can elevate SHBG
• Ageing in men, SHBG rises approximately 1–2% per year after age 40
• Anorexia nervosa, calorie restriction raises SHBG
• Anticonvulsants, phenytoin and carbamazepine induce hepatic SHBG production

What Do Low SHBG Levels Mean?

• Insulin resistance and metabolic syndrome, the most common clinical association
• PCOS, hyperinsulinaemia suppresses SHBG, increasing free androgens
• Obesity - excess adipose tissue promotes insulin resistance and lowers SHBG
• Hypothyroidism, reduced thyroid function lowers SHBG
• Type 2 diabetes, low SHBG is both a risk factor and a consequence
• Androgen excess - anabolic steroid use or androgen-secreting tumours
• Nephrotic syndrome - urinary protein loss includes SHBG

How to Improve Your SHBG Levels

• If SHBG is too low - improve insulin sensitivity through weight loss, exercise, and reducing refined carbohydrates
• Regular exercise - both aerobic and resistance training improve SHBG
• Adequate fibre intake - dietary fibre supports healthy oestrogen metabolism and SHBG
• If SHBG is too high - review medications (OCP, anticonvulsants), check thyroid function
• Optimal thyroid function — treat hypo- or hyperthyroidism to normalise SHBG
• Moderate alcohol — alcohol increases oestrogen and SHBG; reducing intake may help if SHBG is elevated

When Should You Get Tested?

• Women with signs of androgen excess (hirsutism, acne, hair loss) or suspected PCOS
• Men with symptoms of low testosterone despite normal total testosterone
• To calculate the free androgen index
• As part of a metabolic or insulin resistance assessment
• When interpreting borderline testosterone results

Which Lola Health Tests Include SHBG?

SHBG is included in our Hormone 7 panel alongside testosterone, oestradiol, and other reproductive hormones. Also included in Peak Insights. Available as an add-on with any Lola Health blood test.