Does this test have other names?
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 controls the amount of testosterone your body makes.
Most of the testosterone in your blood attaches to 2 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 thinks that you have low or high testosterone, he or she
will first test total testosterone levels. This looks at all 3 types 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 can cause:
Men with low levels of testosterone (hypogonadism) may have:
Loss of sex drive
Testosterone levels in men drop as they age. But this not considered to be hypogonadism.
The FDA currently advises against treating men with low testosterone caused only by
Why do I need this test?
You may need 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 done for men with andropause, or late-onset hypogonadism. This is
a condition caused by decreased testosterone. Men with this condition may have:
Men with HIV/AIDS may also have low testosterone levels.
Signs and symptoms of high testosterone in women include:
Irregular or no menstruation
Extra hair growth, especially on the face
Blood sugar imbalance
Thinning hair on the scalp
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 medicines for women.
What other tests might I have along with this test?
Men may have other tests, including:
Blood tests for other hormones. These include tests to check levels of luteinizing hormone (LH), follicle-stimulating
hormone (FSH), thyroid-stimulating hormone (TSH), and prolactin. These are all hormones
made 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. This is an imaging test to look for growths on the gland.
Women may have other blood tests to check:
Androstenedione, total testosterone, and dehydroepiandrosterone sulfate (DHEA-S). These are other types of androgen hormones.
LH, FSH, TSH, and prolactin. These are all hormones produced by the pituitary gland.
Partial 21-hydroxylase deficiency. High-risk groups for this condition include Ashkenazi Jews.
What do my test results mean?
Test results may vary depending on your age, gender, health history, the method used
for the test, and other things. Your test results may not mean you have a problem.
Ask your healthcare provider what your test results mean for you.
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 is done with a blood sample. A needle is used to draw blood from a vein in
your arm or hand. 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?
Having a blood test with a needle carries some risks. These include bleeding, infection,
bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may
feel a slight sting or pain. Afterward, the site may be sore.
What might affect my test results?
Drinking a lot of alcohol can affect men's hormone levels. Obesity and diabetes can
also affect men's testosterone levels.
For women, some 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 illegal drugs you may use.