Rescaling creatinine makes GFR estimation equations generally applicable across populations - validation results for the Lund-Malmö equation in a French cohort of sub-Saharan ancestry

Abstract

Objectives: To make glomerular filtration rate (GFR) estimating equations applicable across populations with different creatinine generation by using rescaled serum creatinine (sCr/Q) where sCr represents the individual creatinine level and Q the average creatinine value in healthy persons of the same population. Methods: GFR measurements (mGFR, plasma clearance of 51Cr-EDTA) were conducted in 964 adult Black Europeans. We established the re-expressed Lund-Malmö revised equation (r-LMR) by replacing serum creatinine (sCr) with rescaled creatinine sCr/Q. We evaluated the r-LMR equation based on Q-values of White Europeans (r-LMRQ-white; Q-values females: 62 μmol/L, males: 80 μmol/L) and Black Europeans (r-LMRQ-Black; Q-values females: 65 μmol/L, males: 90 μmol/L), and the European Kidney Function Consortium equation (EKFCQ-White and EKFCQ-Black) regarding bias, precision (interquartile range, IQR) and accuracy (percentage of estimates within ±10 % [P10] and ±30 % [P30] of mGFR). Results: Median bias of r-LMRQ-White/r-LMRQ-Black/EKFCQ-White/EKFCQ-Black were -9.1/-4.5/-6.3/-0.9 mL/min/1.73 m2, IQR 14.7/14.5/14.5/15.6 mL/min/1.73 m2, P10 25.1 %/34.8 %/30.3 %/37.2 % and P30 74.2 %/84.1 %/80.6 %/83.6 %. The improvement of bias and accuracy when using proper Q-values was most pronounced in men. Similar improvements were obtained above and below mGFR 60 mL/min/1.73 m2 and at various age and BMI intervals, except for BMI<20 kg/m2 where bias increased, and accuracy decreased. Conclusions: GFR estimating equations may be re-expressed to include rescaled creatinine (sCr/Q) and used across populations with different creatinine generation if population-specific average creatinine concentrations (Q-values) for healthy persons are established.