Sex hormone binding globulin (SHBG) is a protein that is produced in the liver and binds to testosterone, dihydrotestosterone (DHT), and estradiol. A blood SHBG test is used to measure this protein level in your blood, but it is most often used to study your testosterone. SHBG is responsible for carrying sex hormones through the blood and into tissue cells and controls the amount of testosterone that can be used.