The hormones testosterone (an androgen), dihydrotestosterone (DHT) (an androgen), and estradiol (an estrogen) are transported in the blood as physiologically inactive forms by the liver protein known as sex hormone binding globulin (SHBG). The amount of hormone that is available for usage by the bodys tissues can change depending on changes in SHBG levels. This test, which assesses the blood level of SHBG, is most frequently used to assess patients for excess or insufficient testosterone. In men, between 45% and 65% of testosterone is typically linked to SHBG in the blood, with the remaining testosterone being weakly and irreversibly attached to albumin (the main protein in the blood).