What is sex hormone binding globulin (SHBG)?
SHBG is a carrier protein that binds testosterone and other sex hormones in the bloodstream, reducing the amount of free (active) hormone available to body tissues.
Sex hormone binding globulin is a protein your liver produces that attaches to testosterone and other sex hormones as they circulate through your blood. Think of it as a biological binder: hormones stuck to SHBG are unavailable to your cells, while hormones not bound (called free testosterone) are active and can do their work.
The amount of SHBG you have directly changes how much testosterone your body can actually use. High SHBG levels mean more testosterone gets locked up and unavailable, even if your total testosterone number looks normal on paper. Low SHBG means a higher proportion of your testosterone stays free and active.
TRT clinics test SHBG alongside total testosterone because the two readings tell different stories. A patient might have adequate total T but high SHBG, leaving them with low free testosterone and persistent low-T symptoms. Conversely, someone with slightly lower total T but very low SHBG could have plenty of active hormone. This distinction shapes whether a clinician adjusts your dose or investigates other causes like liver function, estrogen levels, or medications affecting SHBG production.
Factors like age, body composition, liver health, and estrogen levels all influence SHBG. During your initial assessment at a Florida TRT clinic, your SHBG result helps providers tailor therapy rather than relying on total testosterone alone.