The CKD-EPI Equation and MDRD Study Equation Find Similar Prevalence of Chronic Kidney Disease in Asian Populations

Potential Conflicts of Interest: None disclosed.

IN RESPONSE:

Dr. Sabanayagam and colleagues report that mean estimated GFR when computed with the CKD-EPI equation is higher than with the MDRD Study equation in a young Asian sample (presumably with high GFR) of mixed ethnicity. This confirms our findings in a predominantly U.S. and European sample and is expected because of the form and coefficients for the variables for both equations. Studies with measured GFR must evaluate the accuracy of GFR estimates in Asian persons. The CKD-EPI equation has no “Asian coefficient,” so we suspect that it will not be as accurate in Asian persons as in our study sample. Others (1, 2) have proposed coefficients for use of the MDRD Study equation in China and Japan, but the results are not consistent, and we suggest that further studies be done in these populations. Unlike in our study, Dr. Sabanayagam and colleagues found no large difference in CKD prevalence by using the CKD-EPI equation compared with the MDRD Study equation. Estimates of CKD prevalence depend on many factors other than the estimating equation, including the assay for serum creatinine; distribution of measured GFR in the study sample; distribution of age, sex, and race (factors that are included in the equations); and non-GFR determinants of serum creatinine, such as muscle mass and diet (factors that are not included in the equations) (3). Prevalence of CKD is also affected by markers to assess kidney damage. Through use of the CKD-EPI equation, stage 3 and 4 CKD in Dr. Sabanayagam and colleagues' study was only slightly less prevalent than in our U.S. sample (6.1% vs. 6.7%, respectively) despite a lower mean age, but the prevalence of stage 1 and 2 CKD was substantially higher (15.4% vs. 5.8%, respectively) (see Appendix Table 9 in our article). The latter finding is at least partially due to 1-time ascertainment for urinary albumin–creatinine ratio rather than our method of accounting for persistence in only a subset of persons with microalbuminuria (4). Because of the higher mean estimated GFR, the prevalence ratio of stage 1 to 2 CKD in Dr. Sabanayagam and colleagues' study was higher when estimated by the CKD-EPI equation than when estimated by the MDRD Study equation. We encourage others to compare the performance of the CKD-EPI equation with the MDRD Study equation in estimating measured GFR, in assessing CKD prevalence, and in predicting risk for future events as part of the process of improving GFR estimation and understanding its clinical implications.