The test measures the levels of SHBG (sex hormone binding globulin), in the blood. SHBG is a protein produced in your liver that binds to sex hormones in the blood and is most often used to gather more information about how testosterone works in the body.
SHBG has an important function because it helps control the amount of sex hormones that are actively working in your body. When the SHBG protein binds to sex hormones, your tissues cannot use those hormones. A SHBG test may be recommended if you suspect you have too much or too little of the sex hormone testosterone. Because testosterone levels affect sex drive, maintain muscle mass and help produce sperm.