TruT Free Testosterone Calculator by FPT

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TruT™ by FPT
TruT™ by FPT
The novel, FDA-registered TruT™ algorithm uses modern understanding of molecular interactions to improve the accuracy of free-T calculations. Why TruT™?

If you are investigating a cohort with potentially altered albumin levels, contact us!


Results from the Free Testosterone Calculator by FPT is provided on an “AS IS” and “AS AVAILABLE” basis, and should NOT be used for making diagnostic or therapeutic decisions related to testosterone without prior consultation with your healthcare provider and/ or medical professionals. FPT makes no representations or warranties of any kind, express or implied, as to the operation of the Site or the information, content or materials included on the Site. You expressly agree that your use of the site is at your sole risk. FPT assumes no responsibility for the suitability of these results for any specific purpose, and these results should not be solely relied on in any clinical situations. Your use of the Free Testosterone Calculator by FPT is subject to the Terms of Use, and by using this site you agree to and accept the Terms of Use.

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Why TruT™?

The only FDA-registered free testosterone calculator

  • Improved biophysical characterizations have have suggested the importance of models that consider allosteric coupling of testosterone with dimeric SHBG. This model, as implemented by TruT™ provides the most accurate estimates for free testosterone.
  • Commonly available free testosterone calculators (,, use models of testosterone:SHBG binding (proposed by Vermeulen et al. and Sodergard et. al) which were developed before the crystal structure for SHBG:T complexes were available. These models assume that the two SHBG monomers behave identically in binding testosterone. Detailed experimental data show that the "simplified linear model is erroneous." References.
  • The Endocrine Society has issued position statements which highlights the laboratory- and operator-dependent variability inherent in direct free testosterone measurements. For this reason they advocate for indirect "calculator" based methods References.
  • The TruT™ calculator provides the ideal solution by using measurements of total testosterone, SHBG, and albumin to calculate free testosterone while taking into account the complex, non-linear allostery in SHBG's association with testosterone. TruT™ is the only calculator available that uses this more complex formulation. References