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The testosterone in your body exists in two states: free testosterone and total testosterone.
Testosterone is the most important male hormone; however, women’s bodies make and need testosterone as well. In both men and women, most of the testosterone in your blood is attached to one of two proteins: albumin and sex hormone-binding globulin (SHBG). However, there is some testosterone in the bloodstream that is not attached to either albumin or SHBG. This is what doctors refer to as “free testosterone.”
The combination of your protein-bound testosterone and free testosterone is your "total testosterone," sometimes referred to as bioavailable testosterone.
Most of the time, the testosterone in your blood is "bound" to proteins. But, less frequently, it glides through the blood unbound as "free testosterone."
“Total testosterone” represents all the testosterone in your system in any state— both bound to SHBG and albumin and the testosterone that is "free" or unbound.
Both free and bound testosterone levels decrease as you age and can lead to age-related testosterone deficiency.
If your doctor suspects that you may have low testosterone, you will most likely first be given a simple blood test for your total testosterone. Suppose your total testosterone levels come back as low. In that case, your doctor may follow up with a test for your free testosterone, as this will give your healthcare provider a more accurate picture of your ability to produce adequate amounts of testosterone.
Total testosterone (total T) is measured via a simple blood test. Based upon the results of your total T test, your doctor may follow up with a free testosterone test.
The following chart illustrates the normal total testosterone levels for men and women by "Tanner Stage" and age. The Tanner Scale breaks down the observable signs of puberty into five stages, running from Stage I from about age 10 to Stage V at 15 for boys and about age 8 to 15 for girls.
|
Tanner Stage |
Male |
Female |
|
Testosterone |
Testosterone |
|
|
I |
<3 |
<3−6 |
|
II |
<3−432 |
<3−10 |
|
III |
65−778 |
<3−24 |
|
IV |
180−763 |
<3-27 |
|
V |
188−882 |
5−38 |
|
Adult Male |
Adult Female |
|
|
>18 y: 264-916 |
20 to 49 y: 8−48 |
|
|
>49 y: 3−41 |
Source: LabCorp
To compare so that you can better understand how variable that “so-called” normal levels of testosterone can be, the following chart gives the “normal” testosterone levels from Quest Diagnostics, another respected testing lab. Quest does not use the Tanner Scale but rather indicates the normal ranges for males and females by age.
|
1-5 Years |
≤5 |
≤8 |
|
6-7 Years |
≤25 |
≤20 |
|
8-10 Years |
≤42 |
≤35 |
|
11 Years |
≤260 |
≤40 |
|
12-13 Years |
≤420 |
≤40 |
|
14-17.9 Years |
≤1000 |
≤40 |
|
≥18 Years |
250-1100 |
2-45 |
Source: Quest Diagnostics
If you compare this chart to the first chart from LabCorp, you can see how the “normal” ranges differ. These two charts come from two of the most respected testing labs in the country, and yet they have differences.
That should help you to understand why it can be quite hard to pinpoint what is the "normal" total testosterone level for any given person of any given age. This is precisely why our doctors try to bring every patient to a "target level" that we have found to be optimal for most patients, regardless of age or gender.
Once we determine what your unique optimal level is, we can tailor treatments that will get you in that zone, so you can perform at your personal best, regardless of your age.
It could be more important to your doctor to know your free testosterone level than only your total testosterone. Sometimes, men could be suffering from "low testosterone" even if their levels of "total testosterone" appear in the normal range.
If your standard blood test for total testosterone shows up as normal and yet you are exhibiting symptoms of low testosterone, getting your free testosterone level can shed light on why you may be experiencing signs of testosterone deficiency. In many ways, free testosterone levels are a better predictor of testosterone deficiency symptoms than your total testosterone levels.
Testing free testosterone is also important in patients that may be suffering from metabolic conditions such as diabetes or obesity, which can artificially lower total testosterone levels.
Your free or bioavailable testosterone interactions and influences the use and production of other critical hormones, which in turn, can impact your total testosterone level.
Free Testosterone Levels and Estradiol – Traditionally, testosterone and estrogen have been considered to be male and female sex hormones, respectively. However, estradiol, which is the main form of estrogen, can also play a critical role in male sexual function.
Studies have found that it is, in fact, estradiol in men that is essential for regulating libido (sex drive), erectile function, and adequate sperm production. Estrogen receptors, as well as aromatase, the enzyme that converts testosterone to estrogen, are abundant in the brain, penis, and testis, organs important for sexual function.
Since studies have found that calculated free estradiol concentration in men with subnormal free testosterone concentrations was lower than that in men with normal free testosterone levels, it is reasonable to assume that it is indeed the low estradiol that is common in men with low free testosterone that is mostly responsible with the sexual dysfunction experienced by such men.
Free Testosterone Levels and Thyroid Hormones – Sub-normal levels of thyroid hormones (hypothyroidism) have been associated with low levels of free testosterone in men. This type of low free testosterone (hypogonadism) has been found to be reversible with thyroid hormone replacement therapy.
Studies have found that free testosterone concentrations are reduced in men with primary hypothyroidism, and thyroid hormone replacement normalizes free testosterone concentrations in these men. This suggests that some men presenting with low free testosterone and low thyroid hormone may benefit from thyroid replacement therapy alone, or some may require combined therapies.
Free Testosterone Levels and HGH – Men with sub-optimal free testosterone often also have less than adequate levels of human growth hormone (HGH). Several peer-reviewed studies have concluded that when testosterone replacement therapy is prescribed for older men in combination with HGH therapy, greater improvements in body composition and muscle performance are experienced than when given either therapy alone.
One such study concluded, "supplemental testosterone produced significant gains in total and appendicular lean mass, muscle strength, and aerobic endurance with significant reductions in whole-body and trunk fat. Outcomes appeared to be further enhanced with HGH supplementation."
Free Testosterone Levels and Insulin – Medical researchers have found that low free testosterone levels are common in men with type 2 diabetes and, therefore, may be associated with insulin resistance. Such studies have concluded that free testosterone deficiency is common in men with diabetes, regardless of the type. This has led to an avenue of research that testosterone replacement may be a possible way to treat or prevent adult-onset diabetes in men.
If you have lower than normal testosterone levels per the chart above, it does not mean that you will necessarily be suffering from low testosterone. Everybody is different, and what may be a "normal" level for one person may be low for another. The above normal levels are considered guidelines.
If you fall below the normal range, your doctor will have to take other things into account. Your age, weight, symptoms and lifestyle, all need to be considered before offering a diagnosis of low testosterone and possibly recommending treatments.
There can be a number of causes of low testosterone. Any disease, injury, or condition that negatively affects the testes could result in low testosterone. However, the most common cause of low testosterone, particularly in men over 40, is the normal decline in testosterone levels that occur as men age.
Testosterone production starts in the womb. It continues through adolescence until it reaches its highest level at about the age of eighteen. In most men, their testosterone levels will stay at or pretty close to that maximum level through their 20s. Then, once you are over 30, your testosterone level will start on a steady downward slope. By the time you are over 40, most men will be feeling the negative impacts of low testosterone.
If you are diagnosed with low testosterone, the safest and most effective treatment is testosterone replacement therapy. Testosterone replacement therapy is usually prescribed as a course of daily injections, usually for six months initially. The benefits of testosterone replacement therapy include:
Over the course of your testosterone therapy, you can expect to feel stronger, more fit, and more mentally alert. Your sex life should also improve. As with any medical treatment, individual results will vary. As such, low testosterone treatments should be tailored to your unique needs and lifestyle, so the length of time you need to be continually receiving low testosterone treatment will vary from patient to patient.
Typically, however, low testosterone treatments last from about six months to a year for your first round of Low-T treatment. After that, you will be evaluated for the need to continue your low testosterone treatment.
Now that you know a little bit more about free testosterone and total testosterone levels in men and women, why not take a minute to contact us and learn more about how testosterone replacement therapy can improve your quality of life.
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