What is SHBG? Sex hormone binding globulin explained

SHBG is short for sex hormone binding globulin. It is a protein in your blood, and its job is to carry sex hormones around.

SHBG

The SHBG blood test, if a clinician has asked for SHBG specifically.

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What SHBG does

Testosterone in the blood is either bound to proteins or unbound, which is called free. SHBG is one of the proteins that binds it. MedlinePlus explains that only unbound hormones can act in your tissues, so SHBG helps set how much testosterone is available.

A 2025 review calls SHBG a glycoprotein produced mainly in liver cells that “transports steroid sex hormones and regulates their bioavailability in a variety of tissues” (Biomedicines, 2025).

Why it matters for a testosterone result

A total testosterone test counts both the bound and the free testosterone. It cannot tell you how the two are split. Two men with the same total testosterone can have different amounts of free testosterone if their SHBG differs. That is the reason a clinician may look at SHBG when symptoms and a total testosterone result don’t seem to match.

What high and low SHBG generally mean

• Low SHBG suggests that more testosterone is free.
• High SHBG suggests that less testosterone is available to tissues.

Each has a list of possible causes, and an SHBG number cannot tell you which applies. The page on high SHBG covers what has been linked to a high result.

Do you need the test?

Not everyone does. The Endocrine Society’s guideline bases a diagnosis of low testosterone on symptoms plus consistently low total and/or free testosterone, and brings in SHBG when a condition may alter it. The SHBG test guide explains when SHBG adds something and which order to place. If you have symptoms, see a clinician rather than relying on a single blood marker.