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Free Testosterone

Does this test have other names?

Free T-index

What is this test?

This test measures the amount of unattached, or "free," testosterone in your blood.

Testosterone is a male sex hormone (androgen) that helps male features develop. Testosterone is made in the testes and the adrenal glands. It causes the changes that occur in boys during puberty. Testosterone helps hair and muscles grow. It also helps the penis and testes grow. Testosterone also causes a boy's voice to deepen. Men continue to make testosterone. It boosts sex drive and helps make sperm.

Women's ovaries also make small amounts of testosterone. It helps many organs and body processes in women.

The pituitary gland in your brain regulates the amount of testosterone your body makes. 

Most of the testosterone in your blood attaches to two proteins: albumin and sex hormone binding globulin (SHBG). Some testosterone is not attached to proteins, or free. Free testosterone and albumin-bound testosterone are also referred to as bioavailable testosterone. This is the testosterone that is easily used by your body.

If your healthcare provider suspects that you have low or high testosterone, he or she will first test total testosterone levels. This looks at all three parts of testosterone. The free testosterone can help give more information when total testosterone is low.

Both men and women can have health problems because of low or high levels of testosterone. Women with high levels of testosterone may have polycystic ovary syndrome (PCOS). This condition marked by infertility, lack of menstruation, acne, obesity, blood sugar problems, and extra hair growth, especially on the face.

Men with low levels of testosterone (hypogonadism) can lose their sex drive, have low energy, suffer bone loss, or become infertile. Testosterone levels in men drop as they age, but this not considered to be hypogonadism. The FDA currently recommends against treating men with low testosterone caused only by aging.

Why do I need this test?

You may have this test to find out whether a low sex drive is caused by a low level of testosterone. In recent years, healthcare providers have used testosterone therapy to treat both men and women with low sex drives.

The test is also ordered for men with andropause, or late-onset hypogonadism, a condition caused by decreased testosterone. Men with this condition may have:

  • Anemia

  • Depression

  • Decreased bone density

  • Lack of energy or fatigue

  • Loss of muscle mass

  • Poor concentration

  • Erectile dysfunction or inability to have an orgasm

  • Infertility

Men with HIV/AIDS may also have low testosterone levels. 

Signs and symptoms of high testosterone in women include:

  • Irregular or nonexistent menstruation

  • Excessive hair, especially on the face

  • Blood sugar imbalance

  • Infertility

  • Thinning hair

If you are a man and this test reveals your free testosterone is lower than normal, your healthcare provider may prescribe testosterone therapy. The FDA has not approved any testosterone drugs for women. 

What other tests might I have along with this test?

Men may have other tests, including:

  • Luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and prolactin. These are all hormones produced by the pituitary gland.

  • Sperm analysis. This test counts the number of live sperm in the liquid that a man ejaculates. This test is often used to look for an infertility problem.

  • Testicular biopsy. This is a tissue sample from the testes.

  • MRI of the pituitary gland

Women may have other tests, including:

  • Androstenedione, total testosterone, and dehydroepiandrosterone sulfat (DHEA-S). These are other types of androgen hormones.

  • LH and FSH, TSH, and prolactin. These are all hormones produced by the pituitary gland.

  • Partial 21-hydroxylase deficiency evaluation. High-risk ethnic groups include Ashkenazi Jews. 

What do my test results mean?

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 healthcare provider.

Results of this test are given in picograms per milliliter (pg/mL). Your level of free testosterone is normal if it is 0.3 to 2 pg/mL, or 0.1 to 0.3 percent of your total testosterone levels. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. 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 because your testosterone level can change from morning to evening and from day to day.

Does this test pose any risks?

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. 

What might affect my test results?

Drinking excessive amounts of alcohol can affect men's hormone levels. Conditions including obesity and diabetes can also affect men's testosterone levels.

For women, having certain health conditions, such as PCOS, can increase free testosterone. 

How do I get ready for this test?

You don't need to prepare for this test. But be sure your healthcare provider 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.

Medical Reviewers:

  • Hanrahan, John, MD
  • Sather, Rita, RN