Testosterone Vs Free Testosterone
Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.
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There are two main types of testosterone in the body: total testosterone and free testosterone. Understanding the differences between them is important for diagnosing testosterone deficiency and treating hypogonadism.
Most of testosterone (98%) is bound to proteins, like sex hormone-binding globulin (SHBG) and albumin. The rest is what’s called free, or bioavailable.
What is Testosterone?
Testosterone is the primary sex hormone that's produced by a male's testes and ovaries. It stimulates sex drive, body hair growth and muscle development in boys during puberty and helps keep the reproductive system healthy in women.
As a man ages, testosterone production gradually decreases. This can lead to a wide variety of health problems. Men who have low testosterone levels may feel lethargic, have a loss of muscle mass and strength, experience sex dysfunction, or have difficulty conceiving children.
A blood test to measure testosterone can help your doctor diagnose and treat a number of health problems, including low libido, low bone mass, and a decline in red blood cell production. Measuring testosterone can also be used to monitor a man's response to testosterone therapy (TRT).
When a person takes a test, a blood sample is drawn from their finger or a vein in the arm. A small amount of the sample is placed into a laboratory analyser and a chemical reaction occurs to measure the level of testosterone in the bloodstream.
Most of the testosterone in a man's body is attached to proteins called albumin and sex hormone-binding globulin (SHBG). About 2-5% of the testosterone in the bloodstream is unattached, referred to as "free" testosterone.
The free form of testosterone can act on a wide range of tissues, and it can trigger many important biological functions, such as protein synthesis, DNA rewriting, and hormone-receptor binding. It can also stimulate the secretion of other hormones such as corticosteroids, which have different effects on different tissue types and organs.
Once testosterone reaches the cells it's going to, it binds to specific androgen receptors. These receptors then activate androgen hormone-dependent processes, such as cellular protein synthesis and the transcription of genes.
Testosterone can also stimulate a specific type of hormone release from the pituitary gland. This can lead to a higher production of luteinizing hormone, which tells the ovaries to make more sperm.
A blood test to measure total testosterone can also help your doctor diagnose and treat a number health problems, including low libido, high cholesterol, sex dysfunction, or a decline in red blood cell production. It can also be used to monitor a man's responses to testosterone therapy, which is often prescribed when a man's testosterone levels are too low.
What is Free Testosterone?
A blood test that measures testosterone in your body can tell if you have low testosterone (also called hypogonadism), which causes many common symptoms like fatigue, erectile dysfunction, and low libido. The test also can identify some medical conditions that cause testosterone deficiency.
The majority of the testosterone in your blood is bound to proteins. These include albumin and sex hormone binding globulin. These proteins prevent your tissues from using the testosterone right away.
However, some of the remaining testosterone that's free and unattached is what's known as "bioavailable" or "free testosterone." Bioavailable testosterone is easy for your tissues to use. It can interact with androgen receptors in your skin, sperm cells, heart, liver, and muscles.
Ideally, your healthcare provider should be testing your total testosterone levels as well as your free testosterone levels. They'll take a blood sample from your vein and calculate your total testosterone level.
Your doctor may order a free androgen index (FAI), which is the ratio of total testosterone to free testosterone. FAI is often a better indicator of low testosterone than total testosterone alone.
As men age, their testosterone levels naturally decrease. These changes aren't always a problem, but when they occur it's important to get tested and treated.
When total testosterone levels are low, your doctor might recommend testosterone replacement therapy (TRT), which can raise your total testosterone levels. It's a safe and effective way to boost testosterone.
But free testosterone levels can decline faster than total testosterone, which makes it a good idea to request a blood test that measures both. This can help your healthcare provider pinpoint why you're experiencing low testosterone symptoms despite your total testosterone levels being normal, says Dr. Robert Welliver, a gynecologist at Cleveland Clinic in Ohio.
Your free testosterone is also affected by your SHBG (sex hormone-binding globulin) levels, Dr. Welliver says, which can increase in age as well as with obesity, autoimmune diseases, thyroid problems, infections, and other health issues. If you have an underlying health condition or are taking medications that can affect SHBG levels, it's a good idea to ask your doctor to test your free testosterone as well.
What is Total Testosterone?
Testosterone is a hormone that regulates sex drive and muscle mass in both men and women. It’s also important for bone growth and development.
Testosterone levels increase during puberty and decrease in adults. A lab test measuring total testosterone can help you and your doctor track down a plethora of testosterone-related symptoms and ailments.
Typically, this test is administered by drawing blood from a vein in your arm. It can be performed in a doctor’s office, hospital or laboratory.
The most cost-effective way to measure total testosterone is by using a direct assay that uses immunoassay or mass spectrometry techniques. This allows for greater accuracy and is more convenient and faster suited to busy medical offices and laboratories.
The total testosterone test isn’t for everyone, but those with symptoms akin to hypogonadism, weight gain, or increased body hair may benefit from the test. It’s also a good idea to get your hormone levels checked at regular intervals, since low or high testosterone can affect your quality of life. Fortunately, most insurance plans cover testosterone testing to some degree, so you don’t have to worry about out-of-pocket costs. To learn more about how to find a test that’s right for you, contact your health care provider today!
What is Bioavailable Testosterone?
Bioavailable testosterone is a type of hormone that can be found in the blood. It is not as commonly used as free or total testosterone, but it can help your doctor diagnose certain medical conditions.
The majority of the testosterone in the body is bound to sex hormone binding globulin (SHBG) or to albumin. Only 0.5% to 3% of total testosterone is free and can bind to cell receptors. This is called free testosterone (FT), while the rest is bound to SHBG or to albumin and is called bioavailable testosterone (BT).
While testosterone is normally produced in men during puberty, there are a number of conditions that can cause low levels of the hormone, including thyroid disease, long-lasting illness, and problems with the testicles. When this happens, your doctor may recommend a test to check your testosterone level.
There are several ways to measure total testosterone in your bloodstream, but the most common is by using a test that is used in many medical centers. These tests are called direct assays, and they are very inexpensive and easy to use.
However, they can be inaccurate in some situations. For example, in men with polycystic ovarian syndrome or other conditions that affect insulin levels, the test results for total testosterone can be very misleading. In these cases, measurements of free and bioavailable testosterone are more accurate.
For these reasons, it is generally recommended that you use bioavailable testosterone measurements when evaluating infertile males. Moreover, the measurement of bioavailable testosterone can provide an important clue as to whether or not an infertile man will be successful with fertility treatment.
In older men with a variety of underlying illnesses, bioavailable testosterone can be lower than total testosterone because of elevated SHBG levels. The association of this decrease with the BDI score is particularly significant.
Unlike total testosterone, which is often interpreted in relation to other sex hormones, bioavailable testosterone levels are independent of age, weight loss, and physical activity. They also have a strong negative correlation with BDI scores. Consequently, they can be used to evaluate the potential benefits of testosterone therapy in older men with depressed mood.
Conclusion
The hormone testosterone is an essential male sex hormone which affects sexual development, muscle mass and bone strength. It also supports libido and erectile function, helping to produce secondary sexual characteristics like facial hair and a deeper voice.
It's made by the testes, ovaries and adrenal glands but it's also produced in the liver and brain by enzymes called 5-alpha reductase. The body uses this to metabolise testosterone into two different metabolites, dihydrotestosterone (DHT) and estradiol.
A small proportion of circulating testosterone is bound tightly to a protein called sex hormone-binding globulin (SHBG) but a larger fraction is more weakly bound to albumin. The free or bioavailable fraction of testosterone is a tiny percentage that's unbound from SHBG and is easily available for tissues to use.
Total Testosterone - The Grand Total
A blood test that measures total testosterone will give you an overall picture of how much of the hormone is present in your body. However, it might not be the best way to measure hormone levels if you're taking medications or have certain conditions.
You can have normal total testosterone and low free testosterone, which may lead to symptoms of a hormone deficiency. If you have a hormone deficiency, your doctor might prescribe a low-dose testosterone therapy to raise your free testosterone level.
Free testosterone is not a good indicator of how well you're absorbing the hormone, so it's a better idea to measure it in addition to total testosterone. Free testosterone can be measured using a few different methods but the most accurate and reliable is via equilibrium dialysis. This method is relatively expensive and time consuming but it's also the most accurate
