99mTc-DTPA Renal Dynamic Imaging Method May Be Unsuitable To Be Used as the Reference Method in Investigating the Validity of CDK-EPI Equation for Determining Glomerular Filtration Rate

OBJECTIVE To compare the measurements of glomerular filtration rate (GFR) determined by (99m)Tc-diethylene triamine pentaacetic acid ((99m)Tc-DTPA) renal dynamic imaging with those estimated by Chronic Kidney Disease Epidemiology Collaboration (CDK-EPI) equation and to identify a more accurate measurement of GFR of chronic kidney disease (CKD) patients in clinical practice. METHODS The GFR was determined simultaneously by 3 methods: (a) dual plasma sample clearance method (tGFR); (b) renal dynamic imaging method (dGFR); (c) CDK-EPI equation (eGFR). The tGFR was employed as the reference method. The correlation, regression, and limit of agreement of dGFR and eGFR were used to demonstrate the validity of the two methods. The comparison of bias, precision, and accuracy between dGFR and eGFR was analyzed to identify the most suitable method. The analysis of bias, precision and accuracy was repeated after stratifying patients by a measured tGFR cutpoint of 60 ml·min(-1)·(1.73 m(2))(-1). RESULTS A total of 149 patients were enrolled. Both dGFR and eGFR correlated well with tGFR and the regression equation of dGFR and eGFR against tGFR was respectively Y = -4.289+0.962X (r = 0.919; RMSE = 14.323 ml.min(-1). (1.73 m(2))(-1); P<0.001) and Y = 2.462+0.914X (r = 0.909; RMSE = 15.123 ml.min(-1). (1.73 m(2))(-1); P<0.001). In addition, Bland-Altman analysis showed preferable agreement between the two methods and the reference method. The comparison revealed that eGFR, compared with dGFR, showed better performance on bias and 50% accuracy and similar performance on other indexes in the whole cohort and the lower-GFR subgroup, whereas in the higher-GFR subgroup the difference of the two methods was not significant in all parameters. CONCLUSIONS Although both CDK-EPI equation and renal dynamic imaging can be used to determine the GFR of CKD patients, CDK-EPI equation is more accurate than renal dynamic imaging. As a result, (99m)Tc-DTPA renal dynamic imaging may be unsuitable to be used as the reference method in investigating the validity of CDK-EPI equation.