Two aspects must be evaluated for the adoption of the new equations: predictability and accuracy. Kim et al. [4] evaluated the predictive performance of the 2021 CKD-EPI equations for cardiovascular disease and mortality using data from the KoreaN Cohort Study for Outcome in Patients With Chronic Kidney Disease (KNOW-CKD). This study showed that the 2021 CKD-EPI equations based on creatinine alone and both creatinine and cystatin C did not show superior predictability compared to the original 2009 creatinine-based CKD-EPI equation. The results of this study should be interpreted with caution because of the relatively lower incidence of cardiovascular disease and mortality in the KNOW-CKD cohort than in other CKD cohorts. However, I and other KNOW-CKD investigators have also previously evaluated the predictive performance of the new equations for the risk of kidney failure [5] and found a similar performance of the new equations compared to the original 2009 equation. In both studies, the difference in eGFR between the 2009 and 2021 creatinine-based equations was approximately 3 mL/min/1.73 m². Therefore, the small eGFR difference between the 2009 and 2021 equations is not expected to have a significant impact on the predictive performance. However, in terms of accuracy, a recent Korean study showed that the 2021 creatinine-based equation overestimated the measured GFR such that the median bias was 4.8 mL/min/1.73 m², which was significantly larger than that of the 2009 equation (1.8 mL/min/1.73 m²) [6]. The difference in bias between the equations was almost identical to the difference in eGFR between the equations in the KNOW-CKD studies. Additionally, the 2021 CKD-EPI equation showed less accuracy and overestimated the measured GFR compared with the 2009 equation in the Chinese population [7]. Accordingly, a lower prevalence of CKD using the new equation has been shown across various Asian cohorts, including Korea, China, India, Singapore, and Russia (Central Asia) [8].

The accuracy of the 2021 CKD-EPI equations should be further validated in various Asian cohorts, especially those with cystatin C. However, based on current evidence, there is no benefit in using the new CKD-EPI equations in Asians (Table 1). The new equations reclassify a significant proportion of CKD grade 3 patients close to the threshold of 60 mL/min/1.73 m² to grade 2, which may delay diagnosis and intervention of CKD for many Asian patients. Moreover, the application of the new equations is unlikely to improve the prediction of outcomes in Asian patients. Furthermore, changes in the prevalence of CKD can influence CKD-related research and healthcare policies in Asian countries. Therefore, the adoption of the new CKD-EPI equations requires further discussion among healthcare professionals and other stakeholders in Asian countries. In particular, it requires careful discussion which eGFR equation should be recommended in the next CKD guidelines of the Kidney Disease: Improving Global Outcomes.