Sex Hormone Binding Globulin (SHBG)

All of the sex hormones in your blood are either bound to proteins or unbound (free). Free sex hormones work with your tissues, helping with a variety of bodily functions including bone and muscle growth and reproductive health. Sex hormones that are bound to proteins, such as SHBG, however, cannot work with your tissues.

An SHBG test is most often done if you have signs and/or symptoms of having too much or too little testosterone. Though often considered a male sex hormone, testosterone is present in females in smaller amounts. In both sexes, it helps control your sex drive and contributes to muscle and bone growth.

Your provider will usually look at your SHBG blood test results along with the results of a total testosterone test. This helps your provider estimate how much free testosterone is in your blood.

If your SHBG levels are too low, it means that more of your total testosterone is likely free and available for your body to use. SHBG can also be lower than normal in conditions such as an underactive thyroid, Cushing's syndrome, acromegaly, and obesity, or with testosterone use. Low SHBG is also linked to insulin resistance, and in some people it may signal a higher chance of developing type 2 diabetes over time.

Higher than normal SHBG can be seen in pregnancy, an overactive thyroid, liver scarring (cirrhosis), with oral estrogen treatment, and with some medicines.

It's also normal for SHBG levels to decrease with older age as the production of sex hormones also decreases.