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

testosterone test 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.