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

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 Cr-51-EDTA) were conducted in 964 adult Black Europeans. We established the re-expressed Lund-Malmo 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 mu mol/L, males: 80 mu mol/L) and Black Europeans (r-LMRQ-Black ; Q-values females: 65 mu mol/L, males: 90 mu mol/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 % [P-10 ] and +/- 30 % [P-30 ] of mGFR). Results: Median bias of r-LMRQ-White /r-LMRQ-Black /EKFCQ-White /EKFC (Q-Black) were -9.1/-4.5/-6.3/-0.9 mL/min/1.73 m(2) , IQR 14.7/14.5/14.5/15.6 mL/min/1.73 m (2) , P 10 25.1 %/34.8 %/30.3 %/37.2 % and P-30 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 m(2) and at various age and BMI intervals, except for BMI<20 kg/m(2) 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.