Choosing an appropriate glomerular filtration rate estimating equation: role of body mass index

Abstract

Background: We aimed to investigate the accuracy of different equations in evaluating estimated glomerular filtration rate (eGFR) in a Chinese population with different BMI levels. Methods: A total of 837 Chinese patients were enrolled, and the eGFRs were calculated by three Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations, three full-age spectrum (FAS) equations and two Modification of Diet in Renal Disease (MDRD) equations. Results of measured GFR (mGFR) by the 99Tcm-diathylenetriamine pentaacetic acid (99Tcm-DTPA) renal dynamic imaging method were the reference standards. According to BMI distribution, the patients were divided into three intervals: below 25th(BMIP25), 25th to 75th(BMIP25–75) and over 75th percentiles (BMIP75). Results: The medium BMI of the three BMI intervals were 20.9, 24.8 and 28.9 kg/m2, respectively. All deviations from mGFR (eGFR) were correlated with BMI (p < 0.05). The percentage of cases in which eGFR was within mGFR ±30% (P30) was used to represent the accuracy of each equation. Overall, eGFRFAS_Cr_CysC and eGFREPI_Cr_2009 performed similarly, showing the best agreement with mGFR among the eight equations in Bland-Altman analysis (biases: 4.1 and − 4.2 mL/min/1.73m2, respectively). In BMIP25 interval, eGFRFAS_Cr got − 0.7 of the biases with 74.2% of P30, the kappa value was 0.422 in classification of CKD stages and the AUC60 was 0.928 in predicting renal insufficiency, and eGFREPI_Cr_2009 got 2.3 of the biases with 71.8% of P30, the kappa value was 0.418 in classification of CKD stages and the AUC60 was 0.920 in predicting renal insufficiency. In BMIP25–75 interval, the bias of eGFRFAS_Cr_CysC was 4.0 with 85.0% of P30, the kappa value was 0.501 and the AUC60 was 0.941, and eGFRFAS_Cr_CysC showed balanced recognition ability of each stage of CKD (62.3, 63.7, 68.0, 71.4 and 83.3% respectively). In BMIP75 interval, the bias of eGFREPI_Cr_CysC_2012 was 3.8 with 78.9% of P30, the kappa value was 0.484 the AUC60 was 0.919, and eGFREPI_Cr_CysC_2012 equation showed balanced and accurate recognition ability of each stage (60.5, 60.0, 71.4, 57.1 and 100% respectively). In BMIP75 interval, the bias of eGFRFAS_Cr_CysC was − 1.8 with 78.5% of P30, the kappa value was 0.485, the AUC60 was 0.922. However, the recognition ability of each stage of eGFRFAS_Cr_CysC eq. (71.1, 61.2, 70.0, 42.9 and 50.0% respectively) was not as good as GFREPI_Cr_CysC_2012 equation. Conclusion: For a Chinese population, we tend to recommend choosing eGFRFAS_Cr and eGFREPI_Cr_2009 when BMI was around 20.9, eGFRFAS_Cr_CysC when BMI was near 24.8, and eGFREPI_Cr_CysC_2012 when BMI was about 28.9.