More Accurate eGFR Creatinine Calculation Formula for Japanese Patients Using Insulin Clearance as a Control

Background: There are several formulas to calculate estimated glomerular filtration rate (eGFR), and some formulas devised overseas have been proposed to correct for Japanese patients, but their accuracy has not been sufficiently verified, and a correction method for Japanese patients suitable for the CKD-EPI formula 2021 is unknown. Methods: eGFR by Cr was calculated using the MDRD formula (corrected for Japanese), the Japanese formula, the CKD-EPI formula 2009 (corrected for Japanese), and the CKD-EPI formula 2021, respectively, in 404 patients whose Cr and inulin clearance were measured at our hospital between 2009 and 2018 and for whom high quality results were obtained. The correlations and errors with the inulin clearance values (Cinu) were compared. We also examined the performance of the correction factor for eGFR using the 2021 version of the CKD-EPI formula. Results: The median Cinu was 62.8 mL/min and the interquartile range was 51.5. The correlation coefficients between eGFR and Cinu were 0.862 for the MDRD formula, 0.871 for the Japanese formula, 0.877 for the CKD-EPI formula 2009, and 0.875 for the CKD-EPI formula 2021, in decreasing order of root mean square of the difference between Cinu and eGFR. The root mean square of the difference between Cinu and eGFR was smaller than that of the CKD-EPI 2009, Japanese, MDRD, and CKD-EPI 2021, when the eGFR of the CKD-EPI 2021 was multiplied by 0.824. Conclusion: Although the Japanese formula was the most accurate of the known Japanese eGFR calculation methods, the CKD-EPI formula 2021 with a novel correction factor may be more accurate.