A testosterone test checks the level of this male hormone (androgen) in the blood. Testosterone affects sexual features and development. In men, it is made in large amounts by the testicles . In both men and women, testosterone is made in small amounts by the adrenal glands , and in women, by the ovaries .
The pituitary gland controls the level of testosterone in the body. When the testosterone level is low, the pituitary gland releases a hormone called luteinizing hormone (LH). This hormone tells the testicles to make more testosterone.
Before puberty, the testosterone level in boys is normally low. Testosterone increases during puberty. This causes boys to develop a deeper voice, get bigger muscles, make sperm , and get facial and body hair. The level of testosterone is the highest around age 40, then gradually becomes less in older men.
In women, the ovaries account for half of the testosterone in the body. Women have a much smaller amount of testosterone in their bodies compared to men. But testosterone plays an important role throughout the body in both men and women. It affects the brain, bone and muscle mass, fat distribution, the vascular system, energy levels, genital tissues, and sexual functioning.
Most of the testosterone in the blood is bound to a protein called sex hormone binding globulin (SHBG). Testosterone that is not bound ("free" testosterone) may be checked if a man or a woman is having sexual problems. Free testosterone also may be tested for a person who has a condition that can change SHBG levels, such as hyperthyroidism or some types of kidney diseases.
Total testosterone levels vary throughout the day. They are usually highest in the morning and lowest in the evening.
Why It Is Done
A testosterone test is done to:
- See why a man is having problems in fathering a child (infertility). A low amount of testosterone can lead to low sperm counts.
- Check a man's sexual problems. Having a low level of testosterone may lower a man's sex drive or not allow him to have an erection (erectile dysfunction).
- See whether a high level of testosterone is causing a boy younger than age 10 to have early signs of puberty.
- Find out why a woman is developing male features, such as excessive facial and body hair (hirsutism) and a deep voice.
- Find out why a woman is having irregular menstrual periods.
- See if testosterone-lowering medicines are working in a man with advanced prostate cancer.
- Find the cause of osteoporosis in a man.