This test measures the level of the hormone testosterone in your blood. Testosterone is a male sex hormone that helps masculine features develop. Testosterone is made in the testes and the adrenal glands, and causes the changes that occur in boys during puberty. Testosterone encourages the growth of hair and muscles, as well as the penis and testes. Testosterone also causes a boy's voice to deepen. Grown men continue to make testosterone, which promotes sex drive and encourages the production of sperm.
Women's ovaries also produce small amounts of testosterone.
Normally, the hypothalamus area of the brain controls the pituitary gland, which regulates the amount of testosterone your body makes. If testosterone levels are too low or too high, you can have problems with sex drive and fertility. Low testosterone, called hypogonadism, is a common problem.
This test is usually done in the morning, because testosterone levels tend to be highest at that time. But you may need to have this test more than once, and at different times of the day, to confirm low testosterone levels. This is necessary because your testosterone level can change from morning to evening and from day to day.
You may need this test if you have symptoms of low testosterone.
Symptoms of low testosterone in men include:
Low sex drive or lack of interest in sex
Difficulty getting an erection
Low sperm count and other fertility problems
Changes in the testicles
Loss of muscle mass
Symptoms of low testosterone in women include:
Missed or irregular menstrual periods
Low sex drive
Changes in breast tissue
Your doctor may order other blood tests to check hormone levels, including:
Follicle-stimulating hormone, or FSH, test
Luteinizing hormone, or LH, test
You may also need to have:
Biopsy of the testicles
Imaging test, such as an MRI
Tests of the pituitary gland
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
The results of this test are given in nanograms per deciliter (ng/dL). Normal test results show total testosterone levels of:
280 to 1,100 ng/dL for men
15 to 70 ng/dL for women
If your testosterone levels are lower than normal, you may have a condition that affects your testosterone production. If your testosterone levels are higher than normal, you may have a tumor on the testes or ovaries that affects your testosterone production.
The test requires a blood sample, which is drawn through a needle from a vein in your arm. For the most accurate results, the sample is usually taken early in the morning, preferably around 8 o'clock.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Some medications may affect your test results. These include antifungal medications, such as ketoconazole, and hormone medications. Having the test performed late in the day may show that your testosterone level is lower than it really is.
You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.