Testosterone

A testosterone test checks the level of this male Reference hormone Opens New Window (androgen) in the blood. Testosterone affects sexual features and development. In men, it is made in large amounts by the Reference testicles Opens New Window Reference Opens New Window. In both men and women, testosterone is made in small amounts by the Reference adrenal glands Opens New Window Reference Opens New Window; and, in women, by the Reference ovaries Opens New Window Reference Opens New Window.

The Reference pituitary gland Opens New Window Reference Opens New Window controls the level of testosterone in the body. When the testosterone level is low, the pituitary gland releases a hormone called Reference luteinizing hormone (LH) Opens New Window. This hormone tells the testicles to make more testosterone.

Before Reference puberty Opens New Window, the testosterone level in boys is normally low. Testosterone increases during puberty. This causes boys to develop a deeper voice, get bigger muscles, make Reference sperm Opens New Window Reference Opens New Window, 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.

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