Testosterone

Explore care
Reviewed January 25, 2026

Definition

A testosterone test measures the amount of the male hormone, testosterone, in the blood. Both men and women produce this hormone.

The test described in this article measures the total amount of testosterone in the blood. Much of the testosterone in the blood is bound to a protein called sex hormone binding globulin (SHBG). Another blood test can measure the "free" testosterone. However, this type of test is often not very accurate.

As men age, their testosterone levels may drop.The correct answer is fact. Testosterone levels may drop over time as a man ages. This drop is normal and many men don't even notice it. But if levels get too low, some symptoms may develop. See your doctor if you notice changes in your mood or sex drive. Which physical change could be a sign of low testosterone?The correct answer is swollen breasts. Men with low testosterone also may lose body hair and muscle mass. Their testicles may shrink. See your doctor if you notice any of these changes in your body. It is normal for older men to lose all interest in sex.The correct answer is myth. It is normal for older men to have less interest in sex compared to when they were younger. But it is not normal to lose all interest in sex. This could be a sign of low testosterone levels. Tell your doctor if you have lost interest in sex. Treatment may help.Low testosterone can cause trouble getting an erection.The correct answer is fact. Low testosterone can make it difficult to get or keep an erection. It can also lead to low sperm counts. Erection problems are also called erectile dysfunction, or ED. Health problems, such as high blood pressure, and many medications can also cause ED. See your doctor to find out what may be causing ED.Which emotional change could be a sign of low testosterone?The correct answer is all of the above. Some men also have hot flashes as testosterone levels drop. Emotional changes can make it hard to work, sleep, or do things you enjoy. Be sure you talk with your doctor if these symptoms occur.A simple blood test can detect low testosterone.The correct answer is fact. If you have ED, have lost interest in sex, or have other symptoms such as swollen breasts, your doctor may check for low testosterone. To do the test, your doctor will draw a sample of blood. Sometimes, more than one blood test is needed to accurately diagnose low testosterone.Aging is the only cause of low testosterone.The correct answer is false. Some medications, some cancers, problems with genes, injury to the testicles and other health problems can cause low testosterone. Your doctor can do tests to find out what is causing low testosterone.Low testosterone can make a man's bones weaker.The correct answer is fact. Low testosterone can lead to osteoporosis, a condition that causes thinner bones that may break more easily. If you have low testosterone, your doctor may recommend a bone density test to see if you have osteoporosis.Testosterone therapy can help:The correct answer is all of the above. Testosterone therapy means taking testosterone to bring levels closer to normal. This can reduce the changes caused by low testosterone, but not everyone responds to testosterone therapy.Testosterone therapy is a good idea for all older men.The correct answer is myth. Some men don't need treatment for low testosterone because they don't have symptoms. Testosterone therapy isn't a good idea for healthy older men who don't have low testosterone. It may increase the risk of prostate cancer. Your doctor can help you decide if testosterone therapy is right for you.

Alternative Names

Serum testosterone

How the Test is Performed

A blood sample is taken from a vein. The best time for the blood sample to be taken is between 7 a.m. and 10 a.m. A second sample is often needed to confirm a result that is lower than expected.

How to Prepare for the Test

Your health care provider may advise you to stop taking medicines that may affect the test.

How the Test will Feel

You may feel a slight prick or sting when the needle is inserted. There may be some throbbing afterward.

Why the Test is Performed

This test may be done if you have symptoms of abnormal male hormone (androgen) production.

In males, the testicles produce most of the testosterone in the body. Levels are most often checked to evaluate signs of abnormal testosterone levels such as:

  • Early or late puberty (in boys)
  • Infertility, erectile dysfunction, low level of sexual interest, or thinning of the bones (in men)

In females, the ovaries produce most of the testosterone. The adrenal glands can also produce too much of other androgens that are converted to testosterone. Levels are most often checked to evaluate signs of higher testosterone levels in women, such as:

  • Acne, oily skin
  • Change in voice
  • Decreased breast size
  • Excess hair growth (dark, coarse hairs in the area of the moustache, beard, sideburns, chest, buttocks, inner thighs)
  • Increased size of the clitoris
  • Irregular or absent menstrual periods
  • Male-pattern baldness or hair thinning

Normal Results

Normal measurements for these tests:

  • Male age 17 to 50 years: 249 to 836 nanograms per deciliter (ng/dL), 8.6 to 29.0 nanomoles per liter (nmol/L)
  • Male age over 50 years: 193 to 740 ng/dL, 6.7 to 25.7 nmol/L
  • Female age 17 to 50 years: 8.4 to 48.1 ng/dL, 0.3 to 1.7 nmol/L
  • Female age over 50 years: 2.9 to 40.1 ng/dL, 0.1 to 1.4 nmol/L

The examples above are common measurements for results for these tests. Normal value ranges may vary slightly among different labs. Some labs use different measurements or test different specimens. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

Certain health conditions, medicines, or injury can lead to low testosterone. The testosterone level also naturally drops with age. Low testosterone can affect sex drive, mood, and muscle mass in men.

Decreased total testosterone may be due to:

  • Chronic illness
  • The pituitary gland does not produce normal amounts of some or all of its hormones
  • Problem with areas of the brain that control hormones (hypothalamus)
  • Low thyroid function
  • Delayed puberty
  • Diseases of the testicles (trauma, cancer, infection, immune, iron overload)
  • Benign tumor of the pituitary gland cells that produce too much of the hormone prolactin
  • Too much body fat (obesity)
  • Sleep problems (obstructive sleep apnea)
  • Chronic stress from too much exercise (overtraining syndrome)

Increased total testosterone level may be due to:

  • Resistance to the action of male hormones (androgen resistance)
  • Tumor of the ovaries
  • Cancer of the testes
  • Congenital adrenal hyperplasia
  • Taking medicines or drugs that increase testosterone level (including some supplements)

References

Aleksic S, Bartke A, Lamberts SWJ, Milman S. Endocrine function and aging. In: Melmed S, Auchus RJ, Goldfine AB, Rosen CJ, Kopp PA, eds. Williams Textbook of Endocrinology. 15th ed. Philadelphia, PA: Elsevier; 2025:chap 26.

Bulun SE, Babayev E. Physiology and pathology of the female reproductive axis. In: Melmed S, Auchus RJ, Goldfine AB, Rosen CJ, Kopp PA, eds. Williams Textbook of Endocrinology. 15th ed. Philadelphia, PA: Elsevier; 2025:chap 15.

Pitteloud N, Papadakis GE, Jacobs AN. Physiology and disorders of puberty. In: Melmed S, Auchus RJ, Goldfine AB, Rosen CJ, Kopp PA, eds. Williams Textbook of Endocrinology. 15th ed. Philadelphia, PA: Elsevier; 2025:chap 23.

Swerdloff RS, Wang C. The testis and male hypogonadism, infertility, and sexual dysfunction. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 216.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright ©2026 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.


Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Health. Please discuss with your doctor any questions or concerns you may have.