his test measures the amount of unattached, or "free," testosterone in your blood.
Testosterone is a male sex hormone (androgen) that helps male features develop. Testosterone is made in the testes and the adrenal glands. It causes the changes that occur in boys during puberty. Testosterone helps hair and muscles grow. It also helps the penis and testes grow. Testosterone also causes a boy's voice to deepen. Men continue to make testosterone. It boosts sex drive and helps make sperm.
Women's ovaries also make small amounts of testosterone. It helps many organs and body processes in women.