What is the Difference between Total Testosterone Level, Free Testosterone, and Bio Available Testosterone ?

In healthy adult men, about 44% of the circulating testosterone is specifically bound to sex hormone–binding globulin (SHBG), 5 50% is non-specifically bound to albumin, and 3.5% is bound to cortisol-binding globulin, indicating that only 2%–3% is unbound or free. SHBG binding decreases the metabolic clearance rate of testosterone and withholds bound hormone from diffusion into the cell, although SHBG may be a necessary co-factor for cellular uptake of testosterone. Whether albumin-bound testosterone can dissociate sufficiently fast to enter tissues is controversial.

Testosterone Calculation Formula
Testosterone Calculation Formula

T                      = Total testosterone

[S]                   = Free testosterone

[S A]                 = Albumin bound testosterone              

[SP]                 = [SHBG] bound testosterone

[Bio T]            = Bio available testosterone

[SHBG]           = Total Sex Hormone Binding Globulin

[P]                   =  free SHBG

For more detailed calculation and examples of calculation you should visit http://www.issam.ch/freetesuit.htm

For Free & Bioavailable Testosterone calculator  you should visit here

Concentrations of non-SHBG-bound testosterone and non-SHBG–nonalbumin– bound testosterone [free testosterone (FT)] are extremely well correlated and interchangeable in most cases. Because concentrations of SHBG vary widely in healthy men and are related to variables such as diet, body mass index (BMI), insulin concentrations, and age, measurements of FT and bioT are valuable for correct assessment of the bioactive fraction of testosterone. In aging men, total testosterone concentrations tend to decrease and SHBG concentrations increase; therefore, measurements of FT and bioT are advocated to support the diagnosis of hypogonadism, which has nonspecific signs and symptoms in elderly men.

WARNING! The calculated free and bioavailable testosterone are reliable in most clinical situations, but should not be relied upon in situations with potential massive interference by steroids binding to SHBG; e.g. in women during pregnancy, in men during treatment inducing high levels of DHT (e.g. transdermal DHT, oral testosterone) or mesterolon.

Recommended references:

  1. http://www.issam.ch/freetesuit.htm
  2. http://www.issam.ch/freetesto.htm
  3. http://www.clinchem.org/cgi/reprint/52/9/1777.pdf

About yuan ade sukma, MD

I'm an Indonesian doctor. I Believe that science and knowledge do not belong to anyone in the world. Science and knowledge is meant to be shared to make the world a better place to live. But if you find any material posted here is violating any copyrights, feel free to contact me and I will delete that. I believe that someday my blog can change the world. I BELIEVE in the POWER of WORDS! Do you..?
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2 Responses to What is the Difference between Total Testosterone Level, Free Testosterone, and Bio Available Testosterone ?

  1. Steven Andler says:

    Hello Dr. Sukma
    I am trying to write a formula to calculate the fdree testonsterone. I was wondering if you could give me the exact formula. The items I have is the SHBG and the Total Testonsterone and I need to find the free testosterone.

    Thank you very much.

    Steven Andler

    • hello, the formula is on the article above, to know your free testosterone level, you need to measure your albumin level, or just assume that your albumin is 4,3 g/dL, put your the SHBG and Total T at the calculator and you can find your free T and Bio T

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