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
pituitary gland controls the level of testosterone in
the body. When the testosterone level is low, the pituitary gland releases a
luteinizing hormone (LH). This hormone tells the
testicles to make more testosterone.
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
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
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
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
- See if testosterone-lowering medicines are working in a man with
- Find the cause of
osteoporosis in a man.
How To Prepare
You do not need to do anything before
you have this test. Your doctor may want you to do a morning blood test because
testosterone levels are highest between 7 a.m. and 9 a.m.