Performance Of Glomerular Filtration Rate Estimation Equations In Elderly Chinese Patients With Chronic Kidney Disease

Objective The Cockcorft-Gault equation (CG equation), simplified MDRD (Modification of Diet in Renal Disease) equation and chronic kidney disease epidemiology collaboration (CKD-EPI) equation have been widely used to estimate glomerular filtration rate(GFR) in patients with chronic kidney disease. However, their agreement with the measured GFR (mGFR) with99mTc-DPTA (the golden standard) in Chinese elderly patients, especially in patients with chronic kidney diseas (CKD) is barely studied. The objective of this study was to evaluate the performance of these equations in elderly Chinese patients with chronic kidney disease.Methods Based on mGFR obtained with the99mTC diethylene triamine pentaacetic acid (99mTc-DTPA) renal dynamic imaging method and standardized by body surface area (BSA),324elderly Chinese patients with CKD were enrolled in this study. Serum creatinine was determined by the enzymatic method. The GFR was estimated using the CG equation, calibrated CG equation, simplified MDRD equation(aMDRD), re-expressed MDRD equation(rMDRD equation), modified MDRD equation for Chinese CKD patients(cMDRD equation) and Chronic kidney disease epidemiology collaboration (CKD-EPI) equation.Their gender, age, height and body weight were recorded. All patients were divided into several kind of groups based on their gender, age or different mGFR level. The patients were divided to high mGFR group [mGFR≥60ml/(min·1.73m2)] and low mGFR group [mGFR<60ml/(min·1.73m2)]. The patients were further divided by the staging standard of Kidney Disease Outcomes Quality Initiative (K/DOQI). Performance in median difference, median percentage difference, median absolute difference, median absolute percentage difference, mean squared predication residual (MSPR), linear correlation, linear regression analysis, receiver operating characteristic (ROC) curve, Bland-Altman plot analysis,15%,30%and50%accuracies of these equations were assessed in the entire population and in subgroups. Data conversion was used to further evaluate the application value of these equations.Nonparametric Wilcoxon rank test was used to compare the bias of the estimated GFR(eGFR) against measured GFR among six equations.χ2test was used to compare the15%,30%and50%accuracies of these equations. Homogeneity of variance test was used to compare the standard deviation of the regression equation of these equations. P<0.05was considered as statistically significant.Results1.In324cases of elderly Chinese patients with CKD, the median difference and median percentage difference of simplified MDRD equation were smaller (P<0.001) than other equations. The median absolute difference, median absolute percentage difference (P<0.001) and MSRP of CKD-EPI equation were smaller than other equations. The15%and30%accuracies of CKD-EPI and50%accuracy of calibrated CG equation were higher (P<0.05) than other equations.2.1n220cases of male elderly CKD patients, the median difference and median percentage difference of simplified MDRD equation were smaller (P<0.001) than other equations. The median absolute difference, median absolute percentage difference (P<0.05) and MSRP of CKD-EPI equation was smaller than other equations. There was no significant difference among15%and30%accuracies of these equations. The50%accuracy of calibrated CG equation and CKD-EPI equation was higher (P=0.01) than other equations.In104cases of female elderly CKD patients, there was no significant difference among the median absolute difference and median absolute percentage difference of these equations (P>0.05).The median difference of simplified MDRD equation and median percentage difference of cMDRD equation the were smaller(P<0.001) than other equations. The MSRP of CKD-EPI equation was smaller than other equations. There was no significant difference between30%and50%accuracies of these equations. The15%accuracy of CKD-EPI equation was higher (P=0.002) than other equations.3. The receiver operating characteristic (ROC) curve showed that the maximum diagnostic accuracy of all the equations for the diagnosis of mild [GFR<90ml/(min·1.73m2)] or moderate renal failure [GFR<60ml/(min·1.73m2)] was not statistically significant (P>0.05).4. In the high GFR level subgroup with a mGFR≥60ml/(min·1.73m2), the median difference, median percentage difference, median absolute difference, median absolute percentage difference (P<0.001) and MSRP of CKD-EPI equation were smaller than other equations. The15%,30%,50%accuracies of CKD-EPI equation were higher (P<0.001) than other equations. In the low GFR level subgroup with a mGFR<60ml/(min·1.73m2), the median difference and median percentage difference of simplified MDRD equation were smaller (P<0.001) than other equations. There was no significant difference among median absolute difference, median absolute percentage difference,30%and50%accuracies among these equations (P>0.05). The15%accuracy of CG equation was higher (P=0.002) and the MSRP of calibrated CG equation was smaller than other equations.5. In different stages of CKD, the CKD stage misclassification of calibrated CG equation was higher and the CKD stage misclassification of CKD-EPI equation was lower (P=0.003).In CKD stage1, there was no significant difference among median absolute difference and median absolute percentage difference of these equations(P>0.05). The median difference and median percentage difference of cMDRD equation was smaller (P<0.001) than other equations.The15%,30%and50%accuracies of CKD-EPI equation were higher (P<0.001) than other equations. None of the other equations had30%accuracy up to the70%level.In CKD stage2, the median difference, median percentage difference, median absolute difference and median absolute percentage difference of CKD-EPI equation were smaller (P<0.001) than other equations. The15%,30%and50%accuracies of CKD-EPI equation were higher (P<0.001) than other equations. None of the other equations had30%accuracy up to the70%level. In CKD stage3, the median difference and median percentage difference of rMDRD equation were smaller (P<0.001) than other equations. There was no significant difference among median absolute difference, median absolute percentage difference,15%and30%accuracies of these equations (P>0.05). The50%accuracy of calibrated CG equation was higher (P<0.05) than other equations.In CKD stages4and5, the median difference and median percentage difference of rMDRD equation were smaller (P<0.001) than other equations. There was no significant difference among the median difference, median percentage difference, median difference absolute value, median absolute percentage difference,15%,30%and50%accuracies of these equations (P>0.05).6.In elderly CKD patients over75years old, the median difference and median percentage difference of rMDRD equation were smaller (P<0.001) than other equations. The median absolute percentage difference (P=0.07) and MSRP of CKD-EPI equation were smaller than other equations. There was no significant difference among median absolute difference of these equations (P>0.05) than other equations. The15%,30%accuracies of CKD-EPI equation and50%accuracy of calibrated CG equation were higher (P<0.05) than other equations.6. In entire population and in low GFR level subgroup, high GFR level subgroup, male elderly subgroup and subgroup over75years old, correlation analysis revealed estimated GFR (eGFR) of these equations were not strongly correlated with mGFR (r<0.8). In female elderly subgroup, correlation analysis revealed eGFR of CKD-EPI equation was strongly correlated with mGFR (r=0.824), while the eGFR of other equations were not strongly correlated with mGFR (r<0.8). Linear regression showed R2value of CKD-EPI equation was better than others in entire population and in all subgroups.7.Bland-Altman plot analysis demonstrated that eGFRs of CG equation, calibrated CG equation and CKD-EPI equation were more consistent with mGFR than the other equations.Conclusions1. In entire population and in all subgroups, CG equation and calibrated CG equation underestimated mGFR. 2. CKD-EPI equation performed better than other equations in entire population, male elderly CKD patients, elderly CKD patients over75years old, high GFR level and CKD stages1and2subgroups. The calibrated CG equation and rMDRD equation performed slightly better than other equations in CKD stage3subgroup. The simplified MDRD equation, cMDRD equation and CKD-EPI equation performed slightly better than other equations in female elderly CKD patients. There was no difference of the performance of these equations in low GFR level and CKD stages4and5subgroups.3.After data conversion, the calibrated CG equation performed better than other equations in entire population, different gender subgroups and the elderly subgroup over75years old. The eGFR of the regression equation of these equations have no significant difference.