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

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(BMI P25 ), 25th to 75th(BMI P25–75 ) and over 75th percentiles (BMI P75 ). Results The medium BMI of the three BMI intervals were 20.9, 24.8 and 28.9 kg/m 2 , 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, eGFR FAS_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/1.73m 2 , respectively). In BMI P25 interval, eGFR FAS_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 AUC 60 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 AUC 60 was 0.920 in predicting renal insufficiency. In BMI P25–75 interval, the bias of eGFR FAS_Cr_CysC was 4.0 with 85.0% of P30, the kappa value was 0.501 and the AUC 60 was 0.941, and eGFR FAS_Cr_CysC showed balanced recognition ability of each stage of CKD (62.3, 63.7, 68.0, 71.4 and 83.3% respectively). In BMI P75 interval, the bias of eGFR EPI_Cr_CysC_2012 was 3.8 with 78.9% of P30, the kappa value was 0.484 the AUC 60 was 0.919, and eGFR EPI_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 BMI P75 interval, the bias of eGFR FAS_Cr_CysC was − 1.8 with 78.5% of P30, the kappa value was 0.485, the AUC 60 was 0.922. However, the recognition ability of each stage of eGFR FAS_Cr_CysC eq. (71.1, 61.2, 70.0, 42.9 and 50.0% respectively) was not as good as GFR EPI_Cr_CysC_2012 equation. Conclusion For a Chinese population, we tend to recommend choosing eGFR FAS_Cr and eGFR EPI_Cr_2009 when BMI was around 20.9, eGFR FAS_Cr_CysC when BMI was near 24.8, and eGFR EPI_Cr_CysC_2012 when BMI was about 28.9.