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Free Testosterone

Does this test have other names?

Free T-index

What is this test?

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

Men and women both make testosterone, a hormone that helps children develop into adult males and females. Most of the testosterone in your blood attaches to two proteins: albumin and sex hormone binding globulin, or SHBG. Some testosterone is unattached to proteins, or free.

It can be important to measure a person's level of free testosterone because this hormone is responsible for sexual traits. When a boy reaches puberty, his body begins to more free testosterone. But as he ages, his testosterone levels can fall and cause health problems.

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

Men with low levels of free testosterone can lose their sex drive, suffer bone loss, or become infertile. 

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 free testosterone. In recent years, health care 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 low 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 health care 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.

Women may have other tests, including:

  • Androstenedione, total testosterone, and dehydroepiandrosterone sulfat, or DHEA-S

  • 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 health care 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.

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 doctor 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.