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What Is Free Testosterone?

By Andy Osborne ; Updated July 27, 2017

Free testosterone is a term that refers to the amount of testosterone in the bloodstream, usually tested in males with certain medical conditions. According to the American Association for Clinical Chemistry (AACC), free testosterone only accounts for 1-4 percent of the testosterone in a typical male's bloodstream.

Testing of free testosterone is often done for a variety of medical reasons, usually (but not always) in men. Examining what free testosterone is, as well as its function and significance, is essential in understanding the role it plays in overall health.


The AACC defines free testosterone as testosterone within the bloodstream that is not bound to any other chemicals. A similar type of testosterone, loosely bound to a chemical called albumin, is often measured in blood tests together with free testosterone to obtain a measurement of bioavailable testosterone, or BAT.

BAT testosterone accounts for only a small part of total testosterone. Much of the body's testosterone is bound to other chemicals, such as globulin.


Free testosterone, says the Testosterone Deficiency Centre, is an integral element in an overall health picture. Typically measured by a blood test, free testosterone levels in the body can be important tools for doctors.

Free testosterone measurement can give a physician a good general indication as to whether a person's hormones are functioning normally. The AACC reports that women as well as males sometimes require tests for free testosterone, since small amounts are needed for hormonal balance.


Measuring free testosterone, according to the AACC, is actually an indirect way to measure a far more important health indicator--the level of sex hormone binding globulin (SHBG) in the bloodstream.

Knowing how much bioavailable testosterone there is in the bloodstream is a way to tell how much is tied up in SHBG. Low levels of SHBG have been linked to steroid use, hypothyroidism (or reduction in thyroid performance) and obesity. High SHBG levels, on the other hand, may indicate hyperthyroidism, cirrhosis and estrogen use, states the AACC.


In addition to the ailments listed above, free testosterone is related--although loosely, according to many endocrinologists--to other health issues, especially in males.

Lack of energy, decreased libido and mood problems have been linked to low free testosterone levels. However, the Testosterone Deficiency Centre states that many endocrinologists declare these to be non-specific symptoms, or symptoms that cannot be directly linked to levels of free testosterone very easily. Still, as men age and their testosterone levels naturally decline, these can indeed be symptoms of low overall testosterone production.


If a doctor discovers a health problem due to abnormal testosterone levels, she may prescribe supplemental testosterone to help with the issue. Many older men receive testosterone injections to improve problems with cognition and memory and to increase energy.

The measurement of free testosterone, while not a perfect system, is still vital for determining overall health when hormone-related problems arise.

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