Free Testosterone Levels

No doubt, maintaining a healthy supply of testosterone is crucial for women and men of any age. When discussing testosterone, it is most often the volume of total testosterone that is of concern. However, in many cases, it is also beneficial to look at free testosterone levels.

What is free testosterone, and why is it important?

Free testosterone is the amount of testosterone unbound in the blood. Because testosterone is a fat-soluble steroid hormone, it cannot move freely through the bloodstream, which is water-soluble. To travel to the body’s many androgen receptors, testosterone must bind to a protein for its transport. Two proteins that bind with testosterone for this purpose are:

• Albumin
• Sex hormone-binding globulin (SHBG)

Before we examine free testosterone levels by age, understanding how free testosterone works is crucial. You see, your body can produce enough total testosterone, but if it remains bound the entire time, it is not bioavailable to the androgen receptors to use. Most of the total testosterone (60 to 90% at any given time) is bound tightly to SHBG and must separate when it reaches its target tissues. Testosterone lightly bound to albumin (most of the remaining amount) is available for the receptors. The remainder (less than 2%) circulates in a free form. Free testosterone cannot circulate far. Once it breaks loose from the protein, it travels to nearby androgen receptors and diffuses into the tissues to enter the cells. The doctor may order a test to check the free testosterone levels by age chart to determine if a man with normal total testosterone experiences problems in the binding if he has Low T symptoms.

Free testosterone levels show how much testosterone is unbound and available to the androgen receptors.

What Is the Difference between Total and Free Testosterone Levels?

When doctors look at total and free testosterone levels, they examine the sum of all testosterone in the bloodstream – that which is bound to SHBG and albumin, as well as the amount that is circulating freely and unbound. That is total testosterone. Free testosterone is that which is unbound and available for the receptor cells. A third measurement is bioavailable testosterone, which includes both the free testosterone as well as that which is loosely bound to albumin. Because the albumin binding is not as tight as with SHBG, that testosterone can readily detach and enter the cells. Only in specific cases will a doctor run that test as it is not as indicative of testosterone deficiency as the others. When testing the range of free testosterone levels, the measurements are not the same as with total testosterone, which is reported as ng/dL (nanograms per deciliter). The reporting of free testosterone levels by age, pg/mL (picogram per milliliter), is the standard measurement used for this test.

Free testosterone levels show only the unbound testosterone, total testosterone shows the entire amount of the hormone in the bloodstream.

Free Testosterone Levels in Males

The more SHBG in the bloodstream, the higher the level of total testosterone and the lower the free testosterone levels in males. The determination of free testosterone levels can tell the doctor where the cause of any symptoms lies. One man can have normal total testosterone but low free testosterone while another can have low total buy normal free testosterone. We often see the later in men who are overweight or obese. The following chart shows free testosterone levels by age, males over 20 years:

Free testosterone levels in men change throughout the years.

Free Testosterone Levels in Females

When females reach menopausal age, their ovaries decrease and then cease hormone production, including testosterone. It is natural that at that time, free testosterone levels in women decline. While the body continues to supply a small amount of testosterone from the peripheral tissues and adrenals, it cannot make up for what the ovaries once produced. As with males, testosterone in women travels through the bloodstream bound to either SHBG or albumin. When assessing a woman for testosterone deficiency, the doctor may order only the total testosterone or also the test for free testosterone levels. Female serum testosterone measurements are based on the symptoms as well as a woman’s overall health. The normal range of free testosterone for women of any age is 0.0 to 4.2 pg/mL. Obviously, it would be better to be in the mid to high-end of the range, as having no free testosterone means that the androgen receptors cannot carry out their functions.

As with total testosterone, free testosterone levels in women are significantly lower than in males.

When Is a Free Testosterone Levels Test Important?

Total testosterone is the leading test for hypogonadism or Low T. When reviewing total testosterone results, the doctor can determine if levels are very low or very high. Below 300 ng/dL total testosterone is an average assessment of low testosterone. However, a man who has results in the 300 to 500 ng/dL range may also do well to retest and add the check of free testosterone levels. Average results here can show if the problem lies in testosterone not being able to break free from the protein binding, or if it is just that the overall amount of testosterone in the serum is enough to support the needs of the androgen receptors. Today, many people do receive comprehensive testing of total and free testosterone levels. Age plays a factor since testosterone production begins to decline before most people reach their thirtieth birthday. If you have concerns over testosterone or any other hormone levels, please contact Kingsberg Medical for a free consultation via phone. Telemedicine makes it possible for us to help men and women throughout the US receive the best, confidential care for a better future.
Brian Leeber