Age- and gender-specific reference values of estimated glomerular filtration rate in a Caucasian population: Results of the Nijmegen Biomedical Study

Abstract

To the Editor: We recently reported reference values for estimated glomerular filtration rate (eGFR).1Wetzels J.F.M. Kiemeney L.A.L.M. Swinkels D.W. et al.Age- and gender-specific reference values of estimated GFR in Caucasians: the Nijmegen Biomedical Study.Kidney Int. 2007; 72: 632-637Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar Serum creatinine was calibrated against the creatinine assay in the original Modification of Diet in Renal Disease (MDRD) laboratory.2Stevens L.A. Manzi J. Levey A.S. et al.Impact of creatinine calibration on performance of GFR estimating equations in a pooled individual patient database.Am J Kidney Dis. 2007; 50: 21-35Abstract Full Text Full Text PDF PubMed Scopus (167) Google Scholar Recent guidelines advise to calibrate serum creatinine assays against creatinine values traceable to isotope dilution mass spectrometry. The original MDRD equation was re-expressed.3Levey A.S. Coresh J. Greene T. Expressing the Modification of Diet in Renal Disease Study equation for estimating glomerular filtration rate with standardized serum creatinine values.Clin Chem. 2007; 53: 766-772Crossref PubMed Scopus (1326) Google Scholar This new equation is 175 × (standardized serum creatinine (in μmol l−1)/88.4)−1.154 × (age (in years))−0.203 × 0.742 (if female) We recalculated our reference values of eGFR using this new formula and standardized serum creatinine values (see tables provided as Supplementary Table S1). The new values exceed our previously reported values, 5th percentile (p5) values being higher by approximately 10%. An explanation can be found in the reported regression equations.1Wetzels J.F.M. Kiemeney L.A.L.M. Swinkels D.W. et al.Age- and gender-specific reference values of estimated GFR in Caucasians: the Nijmegen Biomedical Study.Kidney Int. 2007; 72: 632-637Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar, 3Levey A.S. Coresh J. Greene T. Expressing the Modification of Diet in Renal Disease Study equation for estimating glomerular filtration rate with standardized serum creatinine values.Clin Chem. 2007; 53: 766-772Crossref PubMed Scopus (1326) Google Scholar, 4Vickery S. Stevens P.E. Dalton R.N. et al.Does the ID-MS traceable MDRD equation work and is it suitable for use with compensated creatinine assays?.Nephrol Dial Transplant. 2006; 21: 2439-2445Crossref PubMed Scopus (140) Google Scholar Levey et al. ignored a seemingly small systematic difference of 3 μmol l−1 between the enzymatic assay and the isotope dilution mass spectrometry values, and intercepts of -2.30 and 2.53, respectively, for the comparisons between the enzymatic method and the Jaffe methods. We and others have used regression equations with intercepts of 10 and 16, respectively.1Wetzels J.F.M. Kiemeney L.A.L.M. Swinkels D.W. et al.Age- and gender-specific reference values of estimated GFR in Caucasians: the Nijmegen Biomedical Study.Kidney Int. 2007; 72: 632-637Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar,4Vickery S. Stevens P.E. Dalton R.N. et al.Does the ID-MS traceable MDRD equation work and is it suitable for use with compensated creatinine assays?.Nephrol Dial Transplant. 2006; 21: 2439-2445Crossref PubMed Scopus (140) Google Scholar These differences in regression equations are likely due to the coefficient of variation of the creatinine assays.4Vickery S. Stevens P.E. Dalton R.N. et al.Does the ID-MS traceable MDRD equation work and is it suitable for use with compensated creatinine assays?.Nephrol Dial Transplant. 2006; 21: 2439-2445Crossref PubMed Scopus (140) Google Scholar Although systematic deviations of 3–10 μmol l−1 appear small and negligible, they clearly affect results of calculations particularly for serum creatinine values <100 μmol l−1. Use of the new formula and standardized serum creatinine values thus results in slightly higher reference values for eGFR. For the individual patient, this is clinically not relevant, particularly in view of the known bias in agreement between eGFR and real GFR, with approximately 80% of values of eGFR lying within 30% of real GFR. Use of the new formula and standardized creatinine values will allow better comparisons between studies and populations. Download .doc (.07 MB) Help with doc files Supplementary Material Table S1. Age- and gender-specific reference values of eGFR in a Caucasian population: results of the Nijmegen Biomedical Study.