LabCorp Vs Quest free testosterone lab ranges: Why are they different?

[madman]

Well aware of Fiers 2018 article.

As I have stated previously I am patiently waiting on the completion of Phase II for the TruT (cFTZ) Algorithm let alone standardization and harmonized reference ranges for Free testosterone which is in the works as we speak.

Phase II should be coming to an end soon enough.

8 years in 2014-2022.

Ravi let alone Bhasin are confident about the validity/soon-to-be commercialization of the TruT Algorithm.

It's going to happen.

He is already pushing the use of the newer calculated method!

Bhasin's latest article.

Testosterone Deficiency in Men

Optimizing Diagnostic Accuracy and Treatment Decisions in Men With Testosterone Deficiency (2021) Shalender Bhasin, MB, BS *, Noelle Ozimek, MSc Abstract Objective: This narrative review offers a guideline-based approach for optimizing diagnostic evaluation and treatment decision-making in...

www.excelmale.com

*Free testosterone concentration is ideally measured using the equilibrium dialysis method, performed under standardized conditions.1,31 Direct tracer analog methods for measuring free testosterone concentrations are inaccurate, and therefore, their use is not recommended.35 Although several equations to estimate free testosterone concentration from total testosterone, SHBG, and albumin concentrations have been published,36-38 the estimation of free testosterone concentration performed using these equations are predicated upon accurate measurements of total testosterone, SHBG, and albumin concentrations.31,35 Furthermore, equations that are based on a linear model of testosterone’s binding to SHBG assume a fixed binding affinity (approximately 1 nM)31 and ignore the competing presence of other sex steroids, such as dihydrotestosterone and estradiol.

*Recent studies using modern biophysical techniques have suggested that the binding of testosterone and estradiol to an SHBG dimer is a dynamic process that involves allosteric interactions between binding sites on each of the 2 SHBG monomers such that the binding affinities of the 2 sites are not equivalent.36,39 The binding of a ligand to the first monomer influences the conformational and energetic states of both the monomers.39 The estimation of free testosterone concentration based on an ensemble allosteric model provides a close approximation of concentrations measured using equilibrium dialysis36;

*the computations of free testosterone concentrations using the ensemble allostery model can be obtained at TruT Free Testosterone Calculator by FPT. Because of dynamic changes in the binding affinity of SHBG upon ligand binding, depending on the ligand and SHBG concentrations, no equation can accurately estimate free testosterone concentration under all conditions.39

 

[Nelson Vergel]

Thanks @madman

Adding this from the site

TruT Free Testosterone Calculator by FPT

Free testosterone calculator by FPT. Improved accuracy of free T calculations.

tru-t.org

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 (issam.ch, nebido.com, pctag.uk) 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

 

[drpub2112]

As long as people understand that most men do well with FT in the 20-30 ng/dL range and many would aim for the higher end it should make no difference.

If you want to get nit-picky than I would use Labcorp FT ED assay.

500726: Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences) | Labcorp

Labcorp test details for Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences)

www.labcorp.com

Hi madman. My Quest lab Free Testosterone (Dialysis) is 169.3 pg/ml with a reference of 35.0 -155.0. That puts me slightly above their reference range. I understand that this test is the most accurate but, that means the converted reference range is only 3.5-15.5 ng/dL.

If 169.3 pg/ml converts to 16.93 ng/dL, how does that relate to what you are saying about men feeling well in the 20-30 ng/dL range?

BTW, since I know you're interested in all things TruT...

My TT using Quest is 756ng/dL using (MS) method and my SHGB is 30. That puts my TruT FT at 26.59 ng/dL, which is in the range you mentioned. Can you help me understand how these values correlate?