Extract

Dear Editor

Narinx et al.1 study sociodemographic, lifestyle, and medical factors associated with variations in calculated free testosterone concentrations in men.1 Their main conclusion is that calculated free testosterone concentrations are most prominently associated with age and BMI.

The authors combined several cohort studies in their meta-analyses, which raises some questions from a laboratory perspective. Free testosterone concentrations were calculated based on total testosterone concentrations quantified using various liquid chromatography coupled to mass spectrometry (LC-MS/MS) methods and on SHBG concentrations measured using different immunoassays.

While the authors deliberately included only cohorts from different regions of the world using LC-MS/MS for the assessment of total testosterone, and using the same formula (Vermeulen formula) to calculate the free testosterone concentrations, they included cohorts using different immunoassays for the SHBG measurements. In the supplemental it is mentioned that the following immunoanalyzers were used: Architect i2000sr (Abbott Laboratories), Immulite 2000 (Diagnostic Products Corp.), Delfia (PerkinElmer), E170 Modular (Roche Diagnostics), and Advia Centaur (Siemens). These instruments use different reagents to measure SHBG, and these different SHBG immunoassays are poorly standardized.2

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