Testosterone is often thought of as the quintessential "male" hormone. Produced mainly in the testes, testosterone is an androgen (i.e., sex hormone) that plays a role in characteristics like muscle mass, bone density, fat distribution, facial and body hair growth, sperm production, sex drive and more.
But not all testosterone in the bloodstream is equally available for your body to use. Learning about the difference between total testosterone and free testosterone can help you better understand how this hormone may be impacting certain aspects of your health.
Defining total testosterone and free testosterone
Total testosterone refers to the entire amount of testosterone circulating in your blood, both bound and unbound. Much of your total testosterone is bound to proteins, like albumin and sex hormone-binding globulin (SHBG). When testosterone is bound to proteins, your tissues are unable to activate testosterone receptors around the body and use the hormone the right way.
Free testosterone, on the other hand, refers only to testosterone that is not bound to proteins. As the “active” form of the hormone, free testosterone can readily bind to receptors and exert its effects on the body. Generally, free testosterone makes up about 2% to 3% of total testosterone.
When should you test total testosterone or free testosterone?
Depending on your health goals and concerns, your healthcare provider may recommend testing total testosterone, free testosterone or both.
Here are some reasons your provider may suggest testing total testosterone:
- To examine symptoms possibly related to low testosterone (e.g., erectile dysfunction, fatigue, depressed mood)
- To investigate potential causes of infertility, low libido or other sexual dysfunction issues
- To monitor testosterone replacement therapy
Testing free testosterone could be helpful:
- If total testosterone levels are low
- If symptoms suggest low testosterone, but total testosterone is normal
- To clarify if SHBG abnormalities are causing symptoms
- When assessing response to testosterone replacement therapy
- To investigate potential causes of infertility, low libido or other sexual dysfunction issues
A low total testosterone level suggests an androgen deficiency (i.e., low levels of this male sex hormone). There are also some circumstances in which there will be a normal total testosterone level but a low free testosterone level, which is why it can be helpful to have both levels checked.
How to maintain healthy testosterone levels
No matter your age, making healthy lifestyle choices can help support optimal testosterone levels. This includes regular exercise, a consistent sleep schedule and a balanced diet.
Testing your testosterone levels with your healthcare provider’s guidance can also help you understand how your lifestyle choices may affect this important hormone. Labcorp OnDemand’s Comprehensive Testosterone Test measures total testosterone, free testosterone, albumin and SHBG, providing a complete picture.
Labcorp OnDemand also offers a Men’s Health Test that checks total testosterone along with blood sugar, cholesterol and other key health indicators. Have an open discussion with your healthcare provider about whether testosterone testing may be right for you.
