Difference Between Total and Free Testosterone

Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.


Are You Searching to Maximize Your Testosterone Levels?

If that is the case for you, chances are you have encountered terms like total and free testosterone and their meaning versus importance; in this article we explore that battle of hormones: total vs free testosterone.

Total testosterone measures the overall amount present in your body while free testosterone accounts for what can be utilized by tissues within it.

Both measurements play a vital role in understanding hormonal balance and health conditions in general.

Understanding the difference between them can be crucial when seeking to address issues like low libido, muscle mass loss or energy reduction.

By knowing which measure holds more significance for optimizing testosterone levels. Join us as we examine thishormone and explore key elements determining whether total or free testosterone matters more.

Whether you are fitness enthusiasts, middle aged males or simply curious about hormonal health - this article provides insights and knowledge that will enable informed decision-making.

Let's look at the difference and why it matters

Testosterone plays an essential role in many bodily processes, from muscle development and energy levels to libido and sexual function. Unfortunately, not everyone understands the difference between total and free testosterone levels.

Your body stores most of its testosterone in forms such as sex hormone binding globulin and albumin proteins; only a small proportion is unbound and available to your cells.

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Understanding testosterone

Testosterone is produced in Leydig cells of the testes and secreted mainly into seminiferous tubules for transport to tissues.

Some testosterone is converted to dihydrotestosterone (DHT), an anabolic agent with 10 times greater affinity for androgen receptors and exerting its effects through binding them; some is further converted to estradiol via 5-alpha reductase enzymes.

This type of estrogen acts in women as a negative feedback mechanism against LH produced from pituitary gland thus controlling testicular function. 

Nearly 98% of testosterone that enters the bloodstream is bound to proteins like albumin or sex hormone binding globulin (SHBG), meaning it cannot access cell receptors to perform its duties.

However, about two to five percent of total body testosterone found is unbound and this form is known as free testosterone.

Once free testosterone has been unbound it can bind to its receptors in order to trigger its many functions within the body, including cell reproduction and growth.

When unbound, unbound testosterone may also be converted by enzyme 5a-reductase into 5a-dihydrotestosterone which has stronger anabolic effects, making its presence essential for male health.

Therefore it is crucial that healthy men maintain sufficient levels of 5a-dihydrotestosterone in their system.

Testosterone levels in blood

The bloodstream is then released with testosterone. Because it does not dissolve in blood or water, most of the testosterone (95%) is carried by other proteins like SHBG (sex hormone binding globulin) (albumin ). 

The testosterone remains inactive as long as it is bound to protein. The testosterone can only act on tissue once it is released. This has two advantages:

  • The hormone testosterone regulates the activity of testosterone
  • This prevents liver and kidneys deactivating or removing testosterone prematurely.

When testosterone enters the target cell it is bound to receptors that trigger changes in the cell.

The role of total testosterone

Testosterone is an indispensable hormone with various bodily functions. As the primary male sex hormone, testosterone helps build muscle and bone and promote reproductive health as well as regulate the hypothalamus-pituitary-testes axis to promote normal brain functioning.

When testosterone enters the bloodstream, most of it binds with proteins such as sex hormone-binding globulin (SHBG) or albumin and becomes bound testosterone; this form cannot be used by your body in any of its functions.

Only 2-5 percent are available unbound for body use - known as free testosterone.

Blood tests measure the amount of free testosterone present in the body. They typically involve taking blood from a vein sample and performing an immunoassay test using labeled versions of testosterone with low binding affinity to SHBG and albumin proteins.

However this approach is rarely accurate due to protein binding in bloodstream cells containing testosterone molecules that bind most of it.

A better method of measuring free testosterone levels would be using serum analogue immunoassay instead, using labeled versions with reduced binding affinity so they can easily measure free form levels more accurately.

The role of free testosterone

When testosterone is released into the bloodstream, most of it binds to proteins like sex hormone binding globulin (SHBG) and albumin.

Any remaining free testosterone molecules unbound are known as free testosterone; these are important because only this form can bind with androgen receptors in our bodies allowing testosterone to perform important functions such as building muscle mass, improving mood, increasing libido, and supporting reproductive health.

Testosterone levels tend to decrease with age and can be caused by various factors.

These include obesity, which triggers abnormally high production of hormone-binding proteins; autoimmune diseases which cause inflammation that compromises testes function; as well as medical conditions like diabetes or prostate cancer which reduce serum testosterone levels.

Furthermore testosterone levels may decline due to age-related changes in the hypothalamic pituitary-testicular axis.

The difference between total and free testosterone

Testosterone is an essential hormone for both men and women alike, playing an essential role in many bodily processes like muscle growth, bone density maintenance and metabolism.

Furthermore, testosterone regulates sexual drive during puberty in boys as well as men while aiding sexual development during puberty in boys.

Most of the testosterone found in your bloodstream is known as "bound," meaning it has been attached to proteins like sex hormone binding globulin (SHBG) or albumin to help it travel between cells.

Free testosterone, on the other hand, can easily attach itself to androgen receptors inside cells and influence how these receptors' direct protein production.

Measuring both total and free testosterone levels is crucial to understanding how this hormone affects your body and health. Numerous labs offer testosterone tests; however, be mindful that results may vary considerably between labs.

Direct assays provide the most accurate estimate of free testosterone in your body; these involve measuring SHBG and albumin to provide an estimate. Unfortunately, such direct tests can be costly and challenging to conduct in clinical practice, thus negating their use altogether.

What is bioavailable Testosterone?

The term bioavailable testosterone refers to testosterone which is easily available and capable of acting on tissues. Free testosterone is a good example of this, as it has the ability to bind with cell receptors in any way it chooses.

The testosterone that is bound to albumin can also be classified as bioavailable. 

This is because the bond between testosterone and albumin can be easily reversed, meaning that testosterone often switches from active to inactive form. The effect on men is greater, as more testosterone binds with albumin.

This bond between SHBG and remaining testosterone is stronger. High levels of SHBG may reduce the amount of bioavailable and free testosterone.

Bioavailable testosterone measures the amount of testosterone readily available for tissue action. This is determined by adding albumin-bound and free testosterone. 

Natural ways to increase testosterone levels

Testosterone levels typically increase during adolescence and early adulthood, yet many men today are seeing their levels diminish much earlier than would have been expected only decades ago.

Low testosterone can result in symptoms including low libido and infertility. Luckily, there are natural ways to boost testosterone such as getting more sleep, eating foods rich in vitamin D, and exercising regularly - such as increasing their consumption of foods found in a typical mediterranean diet. 

A surefire way to raise free testosterone levels is reducing the amount of SHBG bound to it, such as eating foods high in vitamin D (like salmon, tuna and mackerel) as well as increasing exercise.

Furthermore, magnesium helps prevent proteins from binding with testosterone while zinc increases bioavailable molecules of testosterone.

Stress, dieting and overweight can have an adverse effect on free testosterone levels.

Losing weight through diet and exercise may help increase testosterone levels; additionally it's essential that we eat a balanced diet including proteins, fats, and carbs for maximum effect.

Each can have an enormous influence on both total and free testosterone levels in the body - for instance obesity can reduce SHBG levels leading to decreased total and bioavailable testosterone production.

Conclusion - Understanding Total and Free Testosterone

Testosterone plays an essential role in muscle growth, sexual drive, bone strength and metabolic health.

But many don't realize that testosterone exists in different forms in your bloodstream - most is "bound," attached to proteins such as SHBG or albumin which prevent its immediate use in tissues; those unbound are considered free testosterone.

Testosterone plays an essential role for men as the primary male sex hormone, helping create and repair reproductive tissue, deepen their voices, build muscle mass and supporting sperm production during puberty; increasing libido and increasing sexual desire over a lifetime.

However, an average man's total and free testosterone levels tend to decrease with age, impacting many aspects of health and fitness such as lifting capacity or heart health.

Diseases which alter protein binding to it may also alter testosterone levels - maintaining optimal levels requires a holistic approach including lifestyle modifications, dietary modification and medical therapy as needed.

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  1. Antonio L, Wu FCW, O’Neill TW, Pye SR, Ahern TB, Laurent MR, et al. Low Free Testosterone Is Associated with Hypogonadal Signs and Symptoms in Men with Normal Total Testosterone. The Journal of Clinical Endocrinology & Metabolism. 2016 Jul 1;101(7):2647–57.
  2. Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018 May 1;103(5):1715–44.
  3. Hackett G, Kirby M, Edwards D, Jones TH, Wylie K, Ossei-Gerning N, et al. British Society for Sexual Medicine Guidelines on Adult Testosterone Deficiency, With Statements for UK Practice. J Sex Med. 2017 Dec;14(12):1504–23.
  4. Longcope C, Feldman HA, McKinlay JB, Araujo AB. Diet and sex hormone-binding globulin. J Clin Endocrinol Metab. 2000 Jan;85(1):293–6.
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