SHBGSex hormone-binding globulin
The carrier protein that decides how much of your testosterone is usable.
SHBG (sex hormone-binding globulin) is a liver-made protein that binds sex hormones — testosterone most tightly — and carries them in the blood. Hormone bound to SHBG is largely unavailable to tissues.
It matters because it is why a total testosterone result can mislead. SHBG rises with age and in some conditions, and falls with obesity, insulin resistance and an underactive thyroid — so two people with identical total testosterone can have quite different amounts actually available, which is why guidelines recommend assessing free testosterone when SHBG is likely to be abnormal.
In practice, SHBG is interpreted alongside total testosterone and symptoms rather than alone, and it is one reason hormone results should be read by a clinician rather than off a private lab printout.
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Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
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