The Free Testosterone Blood Test

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What is Testosterone?

Testosterone is a male hormone found in the blood that affects development and sexual features. In men, it is produced by the testicles, whereas in women, it is produced by the ovaries. The adrenal glands in both men and women also produce a small amount of testosterone. The level of testosterone in the body increases when a boy reaches puberty, causing the voice to deepen, body and facial hair to develop, and causes the production of sperm, among other changes. Women have much lower levels of testosterone in the body, but testosterone in both sexes is responsible for muscle mass, fat distribution, and sexual functioning.

Testosterone is usually bound, or connected, to a protein called sex hormone binding globulin. Testosterone that is not bound to this hormone is known as free testosterone. Testing the levels of free testosterone in the blood may be done if the patient is experiencing certain issues.

Why Test Free Testosterone?

A blood test to check the free testosterone levels may be ordered in several cases. Some of these cases are:

  • A man or woman is complaining of a decreased sex drive
  • A man is suffering from erectile dysfunction
  • A boy under 10 years old is showing signs of puberty
  • A man is suffering from infertility (low levels of testosterone may reduce the amount of sperm produced)
  • A woman is developing male characteristics, such as excessive facial hair or a deeper voice
  • A woman is irregular or no menstrual periods
  • To see if testosterone-lowering medications are working
  • A man has symptoms of testosterone deficiency

How is the Test Done?

The test for free testosterone is like many other blood tests. A small amount of blood will be drawn from the arm and sent off to a lab for testing. Although this test can be done at any time and does not require any special conditions (such as fasting), your doctor may order the test to be done in the morning because testosterone levels will be at their highest. A free testosterone test may be ordered in addition to other tests, such as a total testosterone level, a bioavailable testosterone level, or tests for other hormones, such as estrogen.

Understanding the Test Results

Interpreting results from a free testosterone blood test can be tricky. It is important to keep in mind that hormones are complicated, and this test can provide only a small insight into the complicated workings of the body. The results will be reported in picograms of free testosterone per milliliter of blood. The normal range of free testosterone varies by age and gender, so be sure to discuss your personal results with your physician. It is also important to note that not many people get their free testosterone levels measured when they are healthy, so there is often no personal “normal” value with which to compare the test results when there is a problem. The test results may allow your physician to make a diagnosis, prescribe a treatment, or offer information that will lead to further testing.


WebMD Staff. (2008, May 29). Testosterone.

American Association for Clinical Chemistry. (2009, Feb. 11). Testosterone.