Free Testosterone

Free testosterone is a term that refers to the amount of testosterone in the bloodstream, usually tested in males with certain medical conditions. According to the American Association for Clinical Chemistry (AACC), free testosterone only accounts for 1-4 percent of the testosterone in a typical male's bloodstream. Testosterone is the major androgenic hormone made by the testes in males. Its production is stimulated and controlled by luteinizing hormone (LH), which is manufactured in the pituitary gland. In males, testosterone stimulates development of secondary sex characteristics, including enlargement of the penis, growth of body hair and muscle, and a deepening voice. It is present in large amounts in males during puberty and in adult males to regulate the sex drive and maintain muscle mass. Testosterone is also produced by the adrenal glands in both males and females and, in small amounts, by the ovaries in females. In women, testosterone is converted to estradiol, the main sex hormone in females.