A blood protein that binds sex hormones such as testosterone, and is often low in PCOS.

What SHBG is

SHBG is a protein made by the liver and carried in the blood. Its job is to bind sex hormones, especially testosterone and also estrogen. Hormone that is bound to SHBG cannot act directly on body tissues, so it is effectively held in reserve until needed. Only the free portion, the part that is not bound, can enter cells and have an effect. In this way the level of SHBG helps set how much testosterone is truly active at any one time, rather than just the total amount present. That is why two people with the same total testosterone can experience different effects if their SHBG levels differ.

How it relates to PCOS

In PCOS, SHBG levels are often low. The insulin resistance common in this condition tends to reduce how much SHBG the liver makes. When SHBG falls, more free testosterone circulates and can act on the skin and hair follicles. That can contribute to androgen signs such as acne, hirsutism, and scalp hair thinning. For this reason, a low SHBG is sometimes seen as an indirect pointer to metabolic health. For background, see hormones in PCOS and how insulin resistance affects this balance.

How a result is interpreted

SHBG is usually measured by a blood test and is not read on its own. A doctor reads it together with total testosterone and the free androgen index, a calculation that estimates the active portion of testosterone. A low SHBG result is interpreted in the context of your symptoms and cycle pattern, not as a single number. Reference ranges can also differ between laboratories, so values from two labs are not always directly comparable. One value alone does not tell the whole story, so ask a doctor what your result means.

What it means for you

SHBG is one piece of the hormone picture in PCOS, not a test that confirms a diagnosis by itself. It helps a doctor understand how active your androgens are, but it needs to be seen alongside the wider clinical picture. If you have androgen signs or irregular periods, a doctor can judge whether this test is useful for you and explain the result in the context of your overall health. You can read more in what is PCOS. Any decision about testing or treatment should be made with a doctor.

This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.