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Testosterone

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.

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

The 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 low testosterone such as:

  • Early or late puberty (in boys)
  • Infertility, erectile dysfunction, low level of sexual interest, infertility, 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, such as:

  • Acne, oily skin
  • Change in voice
  • Decreased breast size
  • Excess hair growth (thick, dark hair 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 Risks

  • Male: 300 -1,000 ng/dL
  • Female: 15 - 70 ng/dL

Note: ng/dL = nanograms per deciliter

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

What Abnormal Results Mean

Increased testosterone levels 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 medications or drugs that increase testosterone levels

Decreased testosterone may be due to:

  • Chronic illness
  • Condition in which the pituitary gland does not produce normal amounts of some or all of its hormones
  • Injury or disease of the hypothalamus
  • Delayed puberty
  • Diseases of the testicles (trauma, infection, immune)
  • Noncancerous tumor of the pituitary cells that produce too much of the hormone prolactin

References

Swerdloff RS, Wang C. The testis and male sexual function. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 242.


Review Date: 2/20/2014
Reviewed By: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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