To the Editor:
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 variable1 for reporting creatinine-based estimated glomerular filtration rates (eGFRs) in the United States.2,3
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.4
Our analyses were purely mathematical and were done using procedures described previously.5 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).
Figure 1.
Changes caused by switching from the 2009 CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine equation with a race coefficient to the 2021 CKD-EPI creatinine equation refit without the race variable as a function of age (x-axis, 18-92 years) and the 2009 CKD-EPI estimated glomerular filtration rate (eGFR) values (y-axis, 1-105 mL/min/1.73 m2). (A) Contour plots of absolute differences in eGFR (2021 CKD-EPI refit minus 2009 CKD-EPI). Contours were drawn for every 1 mL/min/1.73 m2 difference. Areas where the 2021 CKD-EPI refit eGFR was lower than that in the 2009 CKD-EPI were shaded in red and where it was higher were shaded in green. (B) Contour plots of the relative differences in eGFR (100 × [2021 CKD-EPI refit − 2009 CKD-EPI] / 2009 CKD-EPI). Contours were drawn for every 1% difference. Areas where the 2021 CKD-EPI refit eGFR was lower than that in the 2009 CKD-EPI were shaded in red and where it is higher were shaded in green. (C) Region plots showing discordant chronic kidney disease stages. Areas where the chronic kidney disease stage according to 2021 CKD-EPI refit was higher than that according to 2009 CKD-EPI (ie, eGFR was worse) were shaded in red, and areas where the chronic kidney disease stage was lower (ie, eGFR was better) were shaded in green. In the white areas, chronic kidney disease stages are the same with both equations.
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.
Article Information
Peer Review
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.
Footnotes
Item S1: Formulas
Item S2: MDRD Equation Compared With the 2021 CKD-EPI Refit
Supplementary Material
Items S1 and S2.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Items S1 and S2.