When you have your testosterone levels tested, you'll probably see two numbers: total testosterone and free testosterone. Knowing the difference between these two, and why both are important, helps you understand your results and make informed choices about your health.
What Total Testosterone Measures
Total testosterone is the overall amount of testosterone in your bloodstream. This includes testosterone attached to proteins, specifically sex hormone binding globulin (SHBG) and albumin, along with a small amount that is not bound. When people mention their "testosterone level," they usually mean total testosterone. The normal range is about 300 to 1,000 ng/dL, but this can vary by lab.
Total testosterone is a helpful starting point, but it does not give the full picture. This is because about 98 percent of your total testosterone is attached to proteins and is not directly available for your body to use.
What Free Testosterone Measures
Free testosterone makes up about one to three percent of your total testosterone and is not attached to any protein. This is the biologically active part. It can enter cells, bind to androgen receptors, and create the effects you expect from testosterone, such as muscle maintenance, energy, libido, mood regulation, and cognitive function.
Normal free testosterone ranges are much smaller than total testosterone ranges, typically measured in picograms per milliliter (pg/mL). For adult men, a typical reference range is roughly 5 to 25 pg/mL, though again, lab-specific ranges vary.
Why the Distinction Matters
This is where things become clinically important. A man might have a total testosterone level that appears normal, such as 500 ng/dL. However, if his SHBG is high, much of that testosterone is bound and unavailable. His free testosterone could be low, so his cells are not getting enough active hormone even though the total looks fine. This is why some men with "normal" total testosterone still have symptoms of low T.
SHBG levels increase with age, liver disease, hyperthyroidism, and certain medications. They decrease with obesity, insulin resistance, and hypothyroidism. Understanding your SHBG level helps explain the relationship between your total and free testosterone and gives a more accurate picture of your hormonal status.
Which Test Should You Get?
The short answer is both. A thorough testosterone blood test should include total testosterone, free testosterone (or calculated free testosterone based on total T, SHBG, and albumin), and SHBG. These three values together give a complete picture of your testosterone status. Some providers also check bioavailable testosterone, which includes both free testosterone and the loosely bound albumin fraction. This is the portion of testosterone that is available or almost available for your body to use.
Interpreting Your Results
When looking at your testosterone levels, context matters a lot. A total testosterone level of 400 ng/dL, along with low SHBG and healthy free testosterone, might be just fine. The same total testosterone with high SHBG and low free testosterone could explain serious symptoms. This is why it is important to have a provider who considers the full picture instead of just one number. We interpret your results in the context of your symptoms, age, and goals. Schedule a consultation to get a clear understanding of where you stand.
References
- Bhasin S, et al. Reference ranges for testosterone in men. Journal of Clinical Endocrinology & Metabolism. 2011;96(8):2430–2439.
- Vermeulen A, et al. A critical evaluation of simple methods for the estimation of free testosterone. Journal of Clinical Endocrinology & Metabolism. 1999;84(10):3666–3672.
- Bhasin S, et al. Testosterone therapy in men with hypogonadism. Journal of Clinical Endocrinology & Metabolism. 2018;103(5):1715–1744.