SHBG, sex hormone binding globulin, is a protein made mainly by the liver that binds testosterone in the blood. Hormone bound to SHBG is held in reserve; the unbound, free portion is what your tissues can use. Two men with the same total testosterone can feel completely different because their SHBG differs, which is why a clinician reads total testosterone, free testosterone and SHBG together and never one of them alone.
What SHBG does
Think of total testosterone as everything in the account and free testosterone as what you can spend today. SHBG is the part that is locked up. When SHBG is high, more testosterone is bound and less is free. When it is low, the opposite. The total number can look identical in both cases.
Why total testosterone alone can mislead
A man with a mid range total and high SHBG may have very little free hormone and feel it. A man with a lower total and low SHBG may be fine. A single total reading is a starting point, not an answer, and it is the most over read number on a men's panel.
What moves SHBG
- Age. SHBG tends to rise over time, so free testosterone can fall faster than the total suggests.
- Thyroid. An overactive thyroid raises SHBG; an underactive one lowers it. TSH, Free T4 and Free T3 are read alongside it for this reason.
- Insulin and body composition. Higher insulin and more body fat tend to lower SHBG, which is one reason glucose and hemoglobin A1c belong on the same draw.
- The liver. SHBG is made there, so liver markers like ALT and AST are part of the context.
- Some medications, which your clinician will ask about.
How a clinician uses it
SHBG is never the headline. It is the number that explains the other two. Read with total and free testosterone, estradiol and the thyroid and metabolic markers, it tells a clinician whether your symptoms and your biology line up, and whether the fix is hormonal at all.
How Regener8 approaches it
SHBG, total testosterone and free testosterone are all on the Regener8 panel, drawn together at LabCorp with thyroid and metabolic markers. A board certified clinician reads the three of them side by side with you on a 30 minute video visit, and any next step comes from that picture, not from one marker.
Last updated
June 25, 2026
