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How to use free testosterone levels in the management of men with Low-T.

  • Testing your Testosterone Levels.

  • What you need to know about Low Free Testosterone levels and Total Testosterone Levels.

  • When should free testosterone be measured?

  • What conditions affect free testosterone levels?

  • Which value is better free or total testosterone?

  • How to increase free testosterone levels.

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Man in Lab measuring total testosterone and free testosterone and which is better.

When evaluating the symptoms of Low-T, the gold standard is to measure serum total testosterone. This has been supported by several clinical trials and guideline statements of various professional medical associations. Free testosterone, a component of total testosterone, is often not tested but does have clinical utility that will be described in today’s article.

Testosterone circulates in the body in both bound and unbound forms. The majority of testosterone in the body is bound to proteins such as albumin and sex hormone binding globulin (SHBG). Unbound forms of testosterone are known as free testosterone. Bioavailable testosterone is the fraction of testosterone that is free and loosely bound to albumin (ready to dissociate and be active/free). It is the free testosterone that is biologically active and available to exert an effect on the androgen receptor. Only 2% of circulating testosterone is free. Total testosterone is calculated as the sum of Free testosterone plus SHBG bound testosterone plus Albumin bound testosterone. See the equation below:

Total Testosterone = Free T + SHBG Bound T + Albumin Bound T

Free T = T unbound

Bioavailable T= FT + Albumin Bound T

Normal Testosterone Ranges in the Body

  • Free Testosterone 1-2%

  • Weekly Bound Testosterone to Albumin 50-65%

  • SHBG Tightly Bound Testosterone 30-45%

When free testosterone is ordered from a lab, it can be measured through an assay or indirectly calculated. The gold standard for measuring free testosterone is by tedious process called equilibrium dialysis. The limitations of this test are expense, dependence on total testosterone accuracy, temperature control, sample dilution among other factors. This type of lab testing is often only found in research laboratories and often not performed routinely. The best cost-effective assessment of free testosterone levels is a mathematical calculation using both total testosterone level and SHBG. The equation used for calculating free testosterone is the Vermeulen Equation.

Free testosterone calculator: Visit and place your information within the fields to calculate your free testosterone levels.

An easy way to calculate your free testosterone is multiply your total testosterone by .1-.3%. This can give a good estimate of your free T level.

What can I do to boost my free testosterone levels?

Free testosterone is affected by, Total testosterone, albumin and SHBG concentrations as seen in the above formulas. Boosting your total testosterone levels will improve your free testosterone levels. Conditions that can alter SHBG and albumin levels and ultimately affect free testosterone levels are the following:

Conditions that increase SHBG





Cirrhosis of the Liver




Conditions that decreased SHBG

Insulin resistance

Obesity (may also be increased because of low-T and increase estrogen)

Metabolic Syndrome

Type 2 Diabetes




Anabolic Steroids

Low albumin states (Nephrotic Syndrome)

The clinical utility of ordering a free testosterone level can be during conditions where testosterone levels are normal yet patients are symptomatic. When SHBG are abnormal, accurate identification of free testosterone levels are required.

Two large studies looked at free testosterone levels in men with low testosterone levels. The Veterans Administration analyzed data from 3700 men with hypogonadism. Researchers found that men with symptoms of hypogonadism 15% of men had low free testosterone levels of less than 24pg/mL.

The EMAS Study (European Male Aging Study) was a multi-center study of more than 3,000 men who were given questionnaires related to the diagnoses of androgen deficiency. The authors concluded that men with findings of erectile dysfunction, decreased sexual thoughts and weak morning erections with total testosterone levels less than 230-317ng/dl and free testosterone level < 7ng/ml ( 20pmol/L) correlated best with syndromic late onset hypogonadism.

Free Testosterone Levels Associated with the following symptoms.

Free T 46 : Decreased frequency of morning erections

Free T 81 : Decreased frequency of sexual thoughts

Free T 81 : Erectile dysfunction

Free testosterone levels can be used to utilized to understand a man’s symptoms if testosterone levels are normal and the above noted medical conditions are present. In these cases, symptoms may better correlate with free testosterone and not total testosterone. If free testosterone is low, some practitioners may consider total testosterone irrelevant, given it’s the free testosterone that enters the cell to exert an effect.

In the absence of symptoms of androgen deficiency, conditions that merit measurement of total testosterone and free testosterone levels are the following:


Bone density loss


Exposure to chemotherapy

Exposure to testicular radiation


Chronic narcotic use

Male infertility

Pituitary Dysfunction

Chronic corticosteroid Use


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