Towards Equations for Estimating Glomerular Filtration Rate Without Demographic Characteristics

Dear Editor, Estimated glomerular filtration rate (eGFR) is an essential index for identifying and monitoring chronic kidney disease (CKD). For estimating GFR, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) research group recently proposed two new serum creatinine-based equations without race, eGFRcr(AS) and eGFRcr-cys(AS), to replace the widely used equations eGFRcr(ASR) and eGFRcr-cys(ASR), that considers serum creatinine, cystatin C (CysC), age, sex and race.1–4 The new equations were developed and validated using data mainly from White and Black participants.4 It remains unknown whether they are applicable to plasma samples as well as to non-White and non-Black subjects. The present study addressed these two questions with a focus on twoChinese CKD cohorts and showed that equations based on other blood metabolites could perform better. The two cohorts comprised 52 patients fromGuangzhou (Third Affiliated Hospital) and 135 patients from Macau (KiangWuHospital) for whom serum samples and plasma samples were available, respectively (Tables S1 and S2 for their characteristics). Performance of the equations was examined with reference to the GFR measured by iohexol plasma clearance (mGFR).2,4 The bias and precision of the current and new CKD-EPI equations were similar for the two cohorts (Table 1). The accuracy of all the equations was better for theMacau cohort, as revealed by lower values of the root mean square error and higher values of the percent agreement within 30% of the mGFR (P30), the percent agreement within 20% of the mGFR (P20) and the percent agreement between the mGFR and eGFR categories.5 As plasma samples were used in the Macau cohort, our results suggested that both old and new CKDEPI equations should be applicable to plasma samples. In the subsequent analyses, the data from the two Chinese cohorts were pooled for a larger sample size. A P30 value of 80%–90% is considered acceptable, and a P30 value of 90% or higher is preferred.4 However, P30 values of two new equations without race were less than