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What Is Free Testosterone & Why Should You Test It?

Connor Sellers
Published by Connor Sellers | Senior Coach
Last updated: April 13, 2023

The term “free testosterone” often causes confusion. Some people associate it with cost-free testosterone therapy.

But of course, that’s not what the term actually refers to.

Over the course of my fitness career, and especially in the last few months, I’ve spent hours upon hours researching what free testosterone really is and why it’s so important.

Here’s what I’ve discovered.

Quick Summary

  • Free testosterone is the testosterone in the body that aren't bound to any proteins, and aid in the overall health of the body.
  • To test the levels of free testosterone in your body, blood is drawn from your vein, and sent to a laboratory for analysis.
  • Some side effects of low testosterone levels include low libido, erectile dysfunction, loss of muscle mass, reduced bone density, and anemia.

What Free Testosterone Is And Why It Matters

hormones 3d modelling

Free testosterone is testosterone that isn’t bound to proteins, and it plays an important role in the strength and overall health of the body.

Only 2% to 3% of your total testosterone is unbound or “free.” The rest, 97% to 98%, is bound to two proteins: sex hormone-binding globulin (SHBG) and albumin [1].

Free testosterone is also the most bioavailable testosterone, which means your body can easily use it and benefit from it.

On the flip side, testosterone bound to SHBG and albumin isn’t as available. That’s because attached proteins make it difficult for testosterone to enter the cells [2].

So, free testosterone may be more important than SHBG or albumin-bound testosterone, especially for sexual functions like libido, erections, etc. But more on that in a moment.

Why Test For Free Testosterone Levels?

You should test for free testosterone to assess your body's hormonal state and get to the bottom of the problem.

If you suspect that you suffer from low testosterone, your doctor may order a test to establish your free testosterone levels — instead of your total testosterone levels.

There are three reasons why he’d test you for free T exclusively.

Firstly, free testosterone may better indicate deficiency than total testosterone [3]. So, if your doctor tests you for total testosterone only, he might not realize that you suffer from a deficiency.

Secondly, your levels of free testosterone will help your doctor better diagnose the cause of low testosterone [4].

On top of that, you might have normal total testosterone levels but still have free testosterone deficiency. So, both tests are needed for your doctor to get the whole picture [5].

In most cases, a doctor will first order a screening test to establish your total testosterone levels. This test will measure both free and attached testosterone.

If the results indicate a deficiency, a doctor may then order a test for free testosterone only.

However, some patients have priority over others when it comes to testing [6]:

“Symptomatic patients, such as those with loss of libido, should be screened first, but people who are obese, can’t lose weight, and those with generalized fatigue may also be considered. However, it’s important not to screen everyone because obesity can cause low testosterone, which will resolve with weight loss.”

- Clifton Jackness, MD

So, if you don’t have any symptoms, you might not be a good candidate for either test.

How Is A Free Testosterone Test Conducted?

inserting an injection into skin

A test for free testosterone is conducted as a standard blood test. That means blood will be drawn from a vein in your arm or hand with a needle.

Your blood sample will then be sent to a lab for analysis. You’ll usually have to wait a few days until you get your results.

It’s important to note that testosterone levels fluctuate during the day.

They tend to be at their highest in the morning, which is why experts recommend testing around 10 AM [7].

However, the fluctuation of T levels also means that you might have to undergo two or more tests to confirm your initial results.

Low Testosterone: Side Effects

Low testosterone levels lead to symptoms associated with hypogonadism [8] [9]. These include:

  • Erectile dysfunction
  • Decreased sex drive (low libido)
  • Higher body weight and body fat percentage
  • Loss of muscle mass
  • Reduced bone density
  • Anemia

The side effects may vary based on the total testosterone levels.

For example, men with normal levels of total testosterone but low levels of free T may not experience these symptoms to a great extent.

It’s important to note that women may also suffer from low T levels. The side effects in women are the same as those in men, minus the erectile dysfunction [10].

Check out our article reviewing the 8 best testosterone boosters for men.

High Testosterone: Side Effects

shirtless man showing his stomach and another man in pain

Common side effects of high testosterone levels include [11]:

  • Blood clots
  • Headaches
  • Insomnia
  • Liver disease
  • Acne
  • Increased appetite and weight gain
  • High blood pressure, high cholesterol, and an increased risk of heart attack
  • Lower sperm count, testicle shrinkage, and even impotence — which may also be caused by testosterone deficiency

Women may also suffer from too much testosterone.

These are common side effects of high testosterone levels in women [12]:

  • Deepening of the voice
  • Frontal balding
  • Increased muscle mass
  • Acne
  • Enlarged clitoris
  • Infertility

High testosterone is usually treated with surgery, oral contraceptives, or some other form of testosterone therapy [13] [14].

Other Tests You Might Want To Order

hand view of a person examining a sample

Undergoing additional testing can help your doctor diagnose the cause of your problems.

I’ll list a few tests you might want to consider, along with the total and free testosterone tests.

Additional tests men can have include:

  • Tests for other hormones: Men can test for other hormones that control and affect testosterone production, such as luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin [15] [16] [17].
  • MRI of the pituitary gland: Low testosterone can be caused by a pituitary tumor. A tumor can compress the pituitary gland, controlling testosterone production [18]. An MRI will help your doctor establish any growths on the gland.
  • Sperm analysis: Low testosterone may cause decreased sperm production and, in some cases, lead to infertility [19]. This test will help your doctor establish the health and viability of your sperm.
  • Testicular biopsy: Since testicles produce both sperm and testosterone, you might want to undergo testicular biopsy, a test that could help diagnose the cause of irregular levels of testosterone [20].

In addition to tests for other hormones produced by the pituitary gland, women may have other blood tests for:

  • Androstenedione and dehydroepiandrosterone sulfate (DHEA-S) levels: Androstenedione and DHEA-S are converted to testosterone and estrogen, so disorders may cause unhealthy testosterone production [21] [22].
  • Partial 21-hydroxylase deficiency: This deficiency affects the adrenal glands and may cause excess production of androgen hormones [23].
  • Polycystic ovary syndrome: Women with PCOS frequently have high levels of free and total testosterone [24].

Can Free Testostosterone Test Help Improve The Quality Of Your Life?

Both high and low levels of testosterone can negatively affect the quality of your life. That’s why it pays off to test for free testosterone.

A free testosterone test can help you establish whether your T is in a healthy range. If not, you’ll at least have a better idea of what to do to improve your current situation.

A good doctor should help you do that. You can expect him to prescribe the most appropriate treatment possible.


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