What is a testosterone levels test?

A testosterone levels test measures the amount of testosterone in a sample of your blood. Testosterone is known as a “male” sex hormone, but females have testosterone in smaller amounts.

Testosterone is made by:

  • The testicles (or testes), the part of the male reproductive system that makes sperm
  • The ovaries, the part of the female reproductive system that makes eggs
  • The adrenal glands, organs on top of each kidney that make several hormones

During male puberty, testosterone causes body hair, muscle growth, and a deepening voice. In adult life, it controls sex drive, maintains muscle mass, and helps make sperm. In females, testosterone is important for the growth of bones and muscles, and healthy organs.

There are different forms of testosterone in your blood that may be measured to help diagnose certain health problems. Most of your testosterone is attached to proteins. The proteins prevent your tissues from using the testosterone right away, which helps control the amount of “active” testosterone in your body. Testosterone that’s not attached to proteins is called free testosterone. Free testosterone acts on your tissues.

Three types of blood tests measure these different forms of testosterone:

  • A total testosterone test measures free testosterone and testosterone that’s attached to proteins. This is the most common type of test.
  • A free testosterone test measures only the “active” form of testosterone. This test is less common, but it may be useful for diagnosing certain medical conditions.
  • A bioavailable testosterone test measures free testosterone and testosterone that’s loosely attached to a blood protein called albumin. This test isn’t commonly done. But like a free testosterone test, it may help diagnose certain medical conditions.

Other names: serum testosterone, total testosterone, free testosterone, bioavailable testosterone

What is it used for?

A testosterone levels test may be used with other tests to help:

  • Diagnose the cause of symptoms that could be from testosterone levels that are too high or too low
  • In children and teens, to find out what’s causing:
    • Early puberty
    • Delayed puberty

Testosterone testing is also used to monitor your health if you:

  • Have had an abnormal testosterone test in the past
  • Are taking medicine that may affect your testosterone levels
  • Are a transgender man taking testosterone for masculinizing hormone therapy (also called gender-affirming hormone therapy)

Why do I need a testosterone levels test?

You may need this test if you have symptoms of abnormal testosterone levels.

For males who have gone through puberty, the test is mostly used for symptoms of low T levels (testosterone levels which are too low). Testosterone levels tend to decrease with age. But other health issues may also cause low T, such as thyroid problems, long-lasting illness, or problems with the testicles.

The symptoms of low T may include:

  • Low sex drive
  • Erectile disfunction or “ED” (difficulty getting an erection)
  • Infertility (difficulty getting someone pregnant)
  • Enlarged breasts
  • Lack of face or body hair
  • Thinning bones or anemia without a known cause
  • Loss of muscle mass

For females, the test is mostly used for symptoms of high T levels, such as:

  • Abnormal hair growth on the body or face
  • Hair loss on the head that may be like male-pattern baldness (hair loss at the temples and balding on the top of the head)
  • A voice that gets lower
  • Irregular or no menstrual periods
  • Infertility (difficulty getting pregnant)
  • Acne

What happens during a testosterone levels test?

A blood sample for a testosterone test should be taken in the morning between 7 and 10. During these hours, your testosterone levels are typically the highest.

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

In certain cases, you may need to fast (not eat or drink) for several hours before the test. Ask your provider how you should prepare for a testosterone levels test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Your test results may mean different things depending on which test was done, your age, your symptoms, the results of other tests, and other conditions you may have. So, it’s best ask your provider to explain your test results.

A testosterone level test alone can’t diagnose any health conditions, but abnormal results with symptoms may be a sign of a health problem.

  • In males, low T levels may be caused by different conditions, including:
    • Chronic (long-lasting) diseases such as liver, or kidney disease
    • A pituitary gland disorder
    • Benign tumors (not cancer)
    • Injury to the testicles
    • Alcohol use disorder
    • Certain genetic diseases such as Klinefelter syndrome
  • In females low T levels are normal, but extremely low levels may be a sign of:
    • An adrenal gland disorder
    • A pituitary gland disorder
    • An ovarian disorder
  • In males, high T levels may be caused by:
    • A tumor in the testicles
    • Steroid use
    • An adrenal gland disorder, such as congenital adrenal hyperplasia (CAH)
  • In females, high T levels may be caused by:
    • Polycystic ovary syndrome (PCOS)
    • Ovarian cancer
    • An adrenal gland disorder, such as congenital adrenal hyperplasia (CAH)
    • A disorder of the pituitary gland