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. See an illustration of the pituitary gland.

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.

Most of the testosterone in the blood is bound to a protein called sex hormone binding globulin (SHBG). Testosterone that is not bound ("free") can also be checked if a man is having sexual problems.

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. 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.

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, when testosterone levels are highest.

How It Is Done

The health professional taking a sample of blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Pur pressure to the site and then a bandage.