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What is Free Testosterone and How To Measure It

What is Free Testosterone and How To Measure It

By Mike Kocsis | 10 minutes read | Last updated: September 12, 2021
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  • Medically Reviewed by Dr. George Touliatos

    Evidence Based Research

    Most of us are familiar with testosterone; however, not all know that it has two kinds. One is called “free testosterone”, while the other is called “bound testosterone.”

    The key difference between these two kinds of testosterone is how they exist in the bloodstream. You need to have them in healthy concentrations so that your body can perform all functions normally.

    In this article, we have talked about free testosterone in detail. We have also discussed how you can measure it and which treatment options you have when your free testosterone is low.  

    Free testosterone test in the UK

    If you’ve come here and simply want to order a free testosterone test and are based in the UK, then follow this link for your free testosterone test to purchase our ‘testosterone plus test’ which will give you a full breakdown of your total testosterone.

    Free testosterone vs. total testosterone

    Around 95% to 98% of the testosterone in your body is attached to either albumin or sex hormone-binding globulin (SHBG) proteins; thus, it is called bound testosterone. The rest of the 2% to 5% of the testosterone exists freely in the bloodstream, and it is known as free testosterone. The sum of both free and bound testosterone makes the total testosterone.

    Free testosterone can directly reach a site and attach to the cells without getting the help of any transport protein. On the contrary, bound testosterone needs the assistance of transport proteins like SHBG to reach the target site and enter the cells to perform its function. That is why a high concentration of SHBG in the blood may lead to low free testosterone levels in the blood.

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    What is Bioavailable testosterone

    Free testosterone and albumin-bound testosterone are called bioavailable testosterone. Recent studies show that testosterone attached to albumin becomes available in the capillary bed, which is why it is also referred to as bioavailable testosterone. When you are low on free testosterone, then albumin-bound testosterone may become available and ready to use by the body.

    Testosterone production and secretion

    In men, testosterone is produced by testicles, while in women, it is produced by ovaries. The production of this sex hormone is controlled by the secretion of many other hormones. Let’s see what exactly the testosterone secretion process is.

  • Your brain’s one part releases a hormone called gonadotropin-releasing hormone (GnRH).
  • GnRH travels to the pituitary gland (exists in the brain) and tells it to release luteinizing hormone (LH) into the blood.
  • LH travels to the testicles or ovaries, where it activates special cells which release testosterone.
  • After its production, testosterone is released into the bloodstream. Most of the testosterone gets attached to the albumin or SHBG protein in the blood, and some of it stays unbound and moves freely.
  • Functions of testosterone

    • During puberty, the main role of testosterone is males is to develop secondary sex characteristics like the formation of body hair, growth of facial hair, deepening of the voice, enlargement of the larynx, increase in muscle mass, etc.  
    • It also controls the growth of testicles and increases sex drive.
    • Testosterone is also known to control some central behaviours like dominance and aggression. It also increases confidence level and sense of competitiveness.
    • It is involved in the development of muscle mass and strength. It increases the production of growth hormones which further increase muscle build.
    • It boosts total bone mass. That is why people with testosterone deficiency are prone to bone fractures.
    • It metabolizes body fat and helps people burn excessive fat cells fast.
    • Testosterone also encourages bone marrow to produce more healthy red blood cells. In this way, it may help the circulatory system maintain its health.

    Normal free testosterone levels

    A decrease in testosterone levels with age is a sign of ageing. After 30, the testosterone level starts falling gradually in men. But sometimes, there can be an underlying reason behind this fall in testosterone levels. It could be obesity, diabetes, damage to testes, thyroid dysfunction, pituitary gland dysfunction, and medication side effects.

    The below table shows the optimal total testosterone, free testosterone, and SHBG bound testosterone levels in men.                 


    Total Testosterone


    Free Testosterone


    SHBG Bound Testosterone






























    If your testosterone levels are lower than normal, then you may experience the following symptoms.

    Low testosterone signs in men:

    • Loss of body hair
    • Fatigue, mood changes, and lack of concentration
    • Low sex drive
    • Trouble in maintaining and attaining an erection
    • Decreased semen volume
    • An increase in the total body fat
    • Reduction in the total bone mass
    • Small testicles

    Low testosterone signs in women:

    • Muscle weakness
    • Bone weakness
    • Fatigue and laziness
    • Trouble falling asleep
    • Increase in the bodyweight
    • Low sex drive
    • Fertility issues
    • Vaginal dryness

    If you are experiencing such symptoms, then it is important to get your testosterone levels checked and talk to your doctor to identify what is causing these issues. Low testosterone can have a negative effect on your life. Therefore, the sooner you get its treatment, the better it is for your health and life.

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    How is free testosterone measured?

    There are two important testosterone tests that are used to measure free testosterone concentration. One is called the total testosterone test. It measures the amount of total testosterone as well as the amount of free testosterone. The other test is called the free testosterone test, and it measures the concentration of only free testosterone.

    These tests are simple blood tests where blood is drawn from your vein and stored in a tube that is sent to the laboratory for testing. Testosterone tests are performed in the morning because you have the highest testosterone levels at that time.

    If your test results show that you have low or high testosterone levels, then another test might be performed to confirm the issue. The need to repeat the test occurs because testosterone levels can fluctuate from day to day due to multiple reasons like medication, etc.

    You can also use a free testosterone calculator to measure its value. For this, you need to know the levels of albumin, SHBG, and testosterone in your serum.   

    Why should you test free testosterone levels?

    Suppose you are experiencing low testosterone symptoms, so you decide to have a total testosterone test. When the test results come out, you discover that your total testosterone levels are normal. Still, you experience low testosterone symptoms – so what can be causing this issue?

    There is a possibility that these symptoms are due to the low free testosterone. Studies show that total testosterone deficiency is not the only cause behind these symptoms. You can experience them even if your total testosterone is normal, but you have low free testosterone levels. Therefore, it is important to have your free testosterone levels checked too.

    Sometimes, health care providers may also check only the total testosterone level and ignore the levels of free testosterone. This can lead to misdiagnosis. If you experience low testosterone symptoms, then talk to your doctor about total and free testosterone tests to get his suggestions.

    How to increase free testosterone?

    If you have low testosterone levels, then your doctor will first find the true reason behind this problem. He will then suggest a treatment plan according to the reason.

    Normally, it is first suggested to try natural means to boost your testosterone levels. Following are the natural ways to increase testosterone.

    • Regular exercise can help you elevate testosterone levels. High-intensity and weight lifting exercises are considered more effective.
    • Eating a balanced amount of three essential nutrients (carbs, protein, and fats) may also boost testosterone.
    • Try to reduce regular stress levels.
    • Take a sunbath to increase your vitamin D3 levels which can then increase testosterone.
    • Maintain a healthy lifestyle and get at least eight hours of sleep every day.
    • Reduce the intake of alcohol.
    • Eat testosterone boosting foods like beef, tuna, egg yolk, low-fat milk, beans, etc.

    When natural means fail to increase your low testosterone levels, then it is best to try other treatments like testosterone replacement therapy (TRT).

    TRT is a treatment suitable for people who have abnormally low testosterone. In this treatment, testosterone injections, pellets, gels, patches, etc., are given to the patients to increase their testosterone levels. So far, this treatment has helped many people with their low testosterone.

    Even though it is an effective treatment, it still has some side effects. Therefore, talk to your doctor about the good and bad effects of this treatment before having it.

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    Free testosterone is the testosterone that moves freely in your bloodstream (with no bound proteins) and can easily get absorbed in the cells to perform its functions. Low free testosterone levels in the serum can cause symptoms like fatigue, low sex drive, erectile dysfunction, low bone mass, etc. It is important to get a suitable treatment for low free testosterone so that you can enjoy a healthy life once again.

    References / Resources

    Testosterone Action versus Testosterone Levels: Why SHBG Matters (

    Testosterone — What It Does And Doesn’t Do – Harvard Health

    6 Strange Warning Signs of Low Testosterone | Everyday Health

    Diagnosis and management of testosterone deficiency (

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    Evidence Based Research

    This article has been researched and written based on scientific evidence and fact sheets that have then been crossed checked by our team of doctors and subject matter experts.

    References, sources and studies used alongside our own in-house research have been cited below, most of which contain external clickable links to reviewed scientific paper that contain date stamped evidence.

    Our team of healthcare experts and GMC registered doctors are licensed to UK GMC standards. We strive to provide you with the latest evidence based, researched articles that are unbiased, honest and provide you with accurate insights, statistics and helpful information on the discussed topic to ensure you gain a better understanding of the subject. You can read more about our Editorial Process by clicking here.

    We value your feedback on our articles, if you have a well-researched paper you would like to share with us please contact us.

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    Please contact us to discuss your hormones, we need your total testosterone levels to validate your hormone deficiency. You can order a blood test here.

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    You may have low testosterone depending on the symptoms you have, please contact us to find out how we can help.

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    About the Author: Mike Kocsis

    Mike KocsisMike Kocsis has an MBA with a focus on healthcare administration and is an entrepreneur and medical case manager for Balance My Hormones Ltd which offers medical services in the UK and Europe. Mike has over 20 years of experience in the healthcare sector, much of that working with people who have hormone imbalances. Mike has appeared on podcasts and radio and is an expert speaker on the subject of hormone imbalance. He specialises in Testosterone Replacement Therapy (TRT) and Hormone Replacement Therapy (HRT) and has helped thousands of people suffering from hormone imbalances recover and regain control of their lives. You can follow him on LinkedIn and on the Balance My Hormones YouTube Channel.

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    Last update: September 12th, 2021
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