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Testing Your Testosterone Levels? Know The Difference Between Free T And Total T

Medically reviewed by Rosanna Sutherby, PharmD on Feb 4, 2019. Written by Kathryn Wall. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.


Testosterone is an essential hormone that helps with a number of different functions within the body. As the primary male sex hormone (it's known as an "androgen hormone"), testosterone helps with the production and maintenance of male reproductive tissue and also supports bone and muscle strength. All in all, this hormone has a significant impact on your health and well-being.

Testosterone deficiency (or hypogonadism) often entails an unsettling list of possible symptoms: you might gain weight more easily, for example—and in the form of body fat, not muscle mass. Or you could find yourself with a lower sex drive—and low testosterone levels in men can even contribute to erectile dysfunction.

Or, perhaps, you’ll feel as if a constant lethargy is smothering your mind’s ability to focus, make quick-and-accurate decisions, and feel good.

People with testosterone deficiency may also face cardiovascular risks, experience insulin resistance, or have a decrease in bone mass.

What about high testosterone levels? High testosterone in men can lead to a decrease in sperm count, decreased testicle size, acne, and changes in sexual performance. While higher testosterone levels can be genetic, there other possible causes, as well—including anabolic steroid abuse and certain rare kinds of adrenal tumors.

So, how do you know if you have normal testosterone levels or if your levels are too low or too high?

If you are experiencing these or other warning signs that you might have a testosterone imbalance, then consider checking your testosterone levels with the Everlywell at-home Testosterone Test. Knowing if your body’s testosterone levels are out of balance is important for your long-term health—something that’s true whether you’re a man or woman. (Related: Low testosterone in women)

For both men and women, it’s important to have normal testosterone levels because testosterone is a hormone that’s absolutely essential for healthy metabolism. (For instance, optimal testosterone production helps your body burn body fat and gain more muscle mass.)

Testosterone tests can help you determine if your levels are within the normal testosterone range for your age. These tests measure specific markers in your body—such as total testosterone or free testosterone. The Everlywell Testosterone Test measures your free testosterone levels because this marker can give you a good understanding of why you might be experiencing symptoms of testosterone deficiency.

Why is this the case, though—and what’s the difference between total testosterone and free testosterone, anyway?

Testosterone in the body: free T vs. total T

In men, most testosterone is made by the testes through a complex series of biochemical reactions—which convert cholesterol into testosterone (the adrenal glands also produce some testosterone).

Testosterone molecules are then secreted directly into the bloodstream—where many of them soon bind to other molecules known as sex hormone binding globulin, or SHBG (testosterone, as you may know, is a sex hormone). Other testosterone molecules bind to albumin—an important type of blood protein.

What is free testosterone?

And the rest of your testosterone—the unbound testosterone? This testosterone is—quite appropriately—termed “free testosterone,” or free T, because it isn’t attached to other molecules. Because they don’t attach to other proteins, this type of bioavailable testosterone can be used up by the body. Your body actively uses free T molecules since they are at liberty to enter the body’s cells—unimpeded by SHBG or albumin—to carry out their function as signaling molecules that regulate metabolism and other cellular functions. (Testosterone molecules that are bound to other proteins cannot enter most of your cells.)

If that’s free testosterone, then what's total testosterone?

Total testosterone is a measure of how much testosterone you have in your blood in total—both free and bound. (So you’ll always have a higher level of total T than free T.)

Generally speaking, you’ll have lower levels of free T if you have more SHBG—with more SHBG molecules in your blood, a greater amount of your testosterone will be bound and not at all free.

Free testosterone vs. total testosterone

Suppose a man was experiencing some of the symptoms of hypogonadism (a kind of androgren deficiency characterized by low testosterone)—like low libido, difficulty concentrating, brain fog, and constant low energy. So he decides to measure his total testosterone levels—but discovers that his total T level is perfectly normal. Nevertheless, he’s going through very real, very debilitating symptoms of hypogonadism—so what could be the issue?

It turns out that symptoms of testosterone deficiency aren’t only caused by the total amount of testosterone in your blood. When it comes to hypogonadism, the level of free and bioavailable testosterone matters, too—because free T is what your body has readily available in the bloodstream. So you could have normal total T levels, but still suffer from symptoms of testosterone deficiency because you don’t have normal free testosterone levels (low free testosterone can be due to high SHBG levels in your blood).

Thus, your free T levels can shed light on why you may be experiencing signs of testosterone deficiency—even if your total T levels are normal. According to some research, free T levels are a better predictor of testosterone deficiency symptoms than levels of total T are. What’s more, low levels of total T don’t necessarily point to a testosterone-related health issue, since this might be simply a “side effect” of something else going on in your body.

For example, obesity can lead to a decrease in total testosterone levels since insulin resistance—a common consequence of obesity—lowers SHBG levels, causing total testosterone levels to drop, as well. However, in a scenario like this, free T is often not affected and remains at a normal level.

So while low total testosterone levels tell you that something might not be quite right with your body’s androgen hormone production, low levels of free T can help you pinpoint a possible cause of symptoms.

Experiencing symptoms of testosterone deficiency or imbalance?

The Everlywell at-home Testosterone Test is a quick and easy way to check free T levels to see how your levels compare to normal free testosterone levels for your age. Everything you need to take the test from the comfort of home is included with the kit, and you can easily view your results on our secure, online platform. If your testosterone is too low or high, talk with your healthcare provider to learn more about treatment options. Your healthcare provider might recommend testosterone replacement therapy to help get your levels back to normal.


Unhealthy testosterone levels in men: causes and symptoms

Unhealthy testosterone levels in women: causes and symptoms


References

Antonio L, Wu FC, O'Neill TW, et al. Low Free Testosterone Is Associated with Hypogonadal Signs and Symptoms in Men with Normal Total Testosterone. J Clin Endocrinol Metab. 2016;101(7):2647-2657. doi:10.1210/jc.2015-4106