Sex hormone-binding globulin is a liver-made protein that binds testosterone and estradiol in the bloodstream, regulating how much is free and active. High SHBG (from aging, thyroid issues, or some medications) reduces free testosterone even when total testosterone reads normal; low SHBG (often with obesity or insulin resistance) does the reverse. It is why total testosterone alone can mislead.
Also known as
sex hormone-binding globulin
Related terms
- Free testosterone
- The fraction of testosterone not bound to proteins and available to tissues — often more telling than total.
- TRT
- Prescription testosterone (gel, injection, or pellet) for men with clinically low, symptomatic levels.