The Author Replies:
We would like to highlight 2 results in the interesting analysis from Wang et al.,1 who have studied the prevalence of discordant estimated glomerular filtration rate (eGFR) results between creatinine- (eGFRcrea) and cystatin C- (eGFRcys) based equations in a US population-based cohort selected from the National Health and Nutrition Examination Survey.1 First, we are happy to see that one of the main result of our analysis from European cohorts2 is confirmed in this US cohort. The prevalence of discordant results between eGFRcrea and eGFRcys is lower when the European Kidney Function Consortium (EKFC) equations are considered instead of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. In the National Health and Nutrition Examination Survey cohort, 24% of eGFR results are discordant when EKFC equations are used (both absolute and relative discordance)1; when the CKD-EPI equations are considered, the prevalence of discordant results between eGFRcrea and eGFRcys is 39% and 34%, for the absolute and relative discordance, respectively.2 Second, the authors insist on the fact that the most substantial discordance is observed between creatinine-based CKD-EPI equation and cystatin C-based EKFC.1 It could have been anticipated that the rate of discordance would be larger when both a different biomarker and equation are considered (the larger discordance with the cystatin C-based EKFC is probably also explained by the fact that the sex variable is not present in the EKFC cystatin C-based equation). In a population-based cohort, the impact of both the biomarker or equation on the prevalence of chronic kidney disease and on the rate of discordant results can be largely anticipated by analyzing the bias of the corresponding equations against measured GFR,3,4 as this has been recently reviewed.5 Although indirect, the lower discordance between eGFRcrea and eGFRcys is a strong argument favoring the EKFC equations.2
References
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