What is SHBG and why does it matter for testosterone optimization?
SHBG (sex hormone–binding globulin) is the liver-produced protein that binds testosterone and estradiol in circulation. It determines how much hormone is bioavailable. Reading total testosterone without SHBG is reading half the picture — two men with identical totals can have very different free testosterone depending on SHBG.
Full answer
Sex hormone–binding globulin (SHBG) is a liver-produced protein that binds circulating sex hormones — primarily testosterone and estradiol — and regulates how much remains bioavailable. Free testosterone is the fraction not bound to SHBG (and loosely bound to albumin) and is the fraction your tissues actually use. SHBG is moved by insulin sensitivity, thyroid status, alcohol, body composition, oral estrogens, and certain medications. Low SHBG often co-travels with insulin resistance and elevated free testosterone relative to total. High SHBG suppresses free testosterone even when total is in range and is common with hyperthyroidism, low caloric intake, or oral estrogen exposure. This is why the oMeds biomarker panel reads total testosterone, free testosterone, and SHBG together — and reads them again on the recalibration cadence rather than once at baseline.
Educational. Not a substitute for individualized provider review.
- Testosterone optimization pathway — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29