The 2009 and 2021 CKD-EPI Equations: A Graphical Analysis of the Effect of Refitting GFR Estimating Equations Without a Race Coefficient

The National Kidney Foundation and American Society of Nephrology Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease recommends implementing the 2021 CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine equation refit without the race variable1Inker L.A. Eneanya N.D. Coresh J. et al.New creatinine- and cystatin C-based equations to estimate GFR without race.N Engl J Med. 2021; 385: 1737-1749Crossref PubMed Scopus (154) Google Scholar for reporting creatinine-based estimated glomerular filtration rates (eGFRs) in the United States.2Delgado C. Baweja M. Crews D.C. et al.A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease.J Am Soc Nephrol. 2021; 32: 2994-3015Crossref Scopus (43) Google Scholar,3Delgado C. Baweja M. Crews D.C. et al.A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease.Am J Kidney Dis. 2022; 79: 268-288.e1Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar Here, we provide a systematic visual analysis of the effect on eGFR values when using the 2021 CKD-EPI creatinine equation refit compared with the 2009 CKD-EPI creatinine equation with a race coefficient.4Levey A.S. Stevens L.A. Schmid C.H. et al.A new equation to estimate glomerular filtration rate.Ann Intern Med. 2009; 150: 604-612Crossref PubMed Scopus (14817) Google Scholar Our analyses were purely mathematical and were done using procedures described previously.5Buchkremer F. Segerer S. Estimating glomerular filtration rate: a systematic comparison of the new European Kidney Function Consortium equation with the Chronic Kidney Disease Epidemiology Collaboration equation.Clin Kidney J. 2021; 14: 448-450Crossref PubMed Scopus (3) Google Scholar We solved the 2009 equation for creatinine and used this term in the 2021 refit formula (Item S1). Using the software Mathematica, we designed different contour plots. Contour plots can be considered as topographical maps where 2 variables define the x-axis and the y- axis and a third variable is shown by isolines within this coordinate system. Similar to a topographical map, all sorts of information can be displayed for different spots defined by the 2 coordinates. We demonstrated the absolute and relative differences in eGFRs (Fig 1A and B) between the 2009 equation and the 2021 refit as a function of age (x-axis) and the 2009 eGFR values (y-axis). Because chronic kidney disease (CKD) is classified according to eGFR, we added plots—with the very same coordinate system—where we marked all the age/2009 CKD-EPI regions that have differing CKD classification results between the 2 equations (Fig 1C). In comparison with the 2009 CKD-EPI values, the 2021 refit values were lower for Black persons and higher for non-Black persons. Absolute differences (Fig 1A) are mostly dependent on kidney function, being very small for low eGFRs. Relative differences (Fig 1B) show a race-discordant age dependency: for Black persons, they are highest in young people; and for non-Black persons, they are highest in the elderly. Regions with discordant CKD classification (Fig 1C) are very small for higher CKD stages. (An analogous figure comparing the Modification of Diet in Renal Disease equation with the 2021 CKD-EPI refit can be found in Item S2.) Our plots provide an instant and global picture of the range and distribution of eGFR changes and of the effects on CKD staging that result from switching to the new equation. We believe that these graphics will help clinicians in the transition to the 2021 CKD-EPI creatinine equation refit without the race variable. Received December 8, 2021 as a submission to the expedited consideration track with 2 external peer reviews. Direct editorial input from the Editor-in-Chief. Accepted in revised form January 15, 2022. Download .pdf (4.53 MB) Help with pdf files Supplementary File (PDF)Items S1 and S2.