What is SHBG (sex hormone-binding globulin)?
SHBG is a protein produced by the liver that binds to testosterone and other sex hormones in the bloodstream, reducing the amount of free (active) testosterone available to the body's tissues.
Sex hormone-binding globulin (SHBG) is a protein synthesized by the liver that attaches to testosterone molecules circulating in the blood. When testosterone binds to SHBG, it becomes unavailable to tissues that rely on it, because only free testosterone (the unbound fraction) can enter cells and produce biological effects. Higher SHBG levels mean less free testosterone despite potentially normal total testosterone readings.
SHBG levels vary based on age, body weight, liver function, and other hormonal factors. This is why clinicians order both total testosterone and free testosterone tests rather than relying on total testosterone alone. A man with high SHBG might have adequate total testosterone but insufficient free testosterone, which can explain persistent low-T symptoms. Conversely, low SHBG allows more testosterone to remain free and active.
For testosterone replacement therapy (TRT) patients, SHBG matters during treatment monitoring. Changes in SHBG can affect how much active hormone reaches tissues, influencing dose adjustments and symptom response. Men's health clinics in Florida routinely measure SHBG alongside total and free testosterone to interpret lab results accurately and optimize TRT protocols.