Creatinine clearance estimation after kidney transplantation: an analysis of three methods

Surveillance of glomerular filtration rate (GFR) is essential for the management of kidney transplant recipients. We compared the performance of estimation equations with (99m)Technetium ((99m)Tc)-DTPA clearance (TcGFR) in 32 of our patients, using the Modification of Diet in Renal Diseases (MDRD), Nankivell (NK), and Cockcroft-Gault (CG) formulas. All patients were adequately hydrated before study. (99m)Tc-DTPA was injected intravenously (maximal dose = 37 MBq). A second syringe was prepared for an aliquot of the study ("standard"). Blood was sampled at 120 and 240 minutes in various sites. After centrifugation, 1.0 mL plasma was transferred into a counting vial. Both the samples and the "standard" were measured in a well counter. The mean time from transplantation to TcGFR was 47.9 months (range, 4-143 months). The mean serum creatinine level was 124 micromol/L (range, 70-371 micromol/L). The mean TcGFR was 58.6 mL/min/1.73 m(2) (range, 14-100 mL/min/1.73 m(2)). The MDRD equation showed a median difference of 1.4 mL/min/1.73 m(2) with 81.2% of estimated GFR within 20% of TcGFR. Median differences were 8.94 and 11.47 mL/min/1.73 m(2) for NK and CG formulas, respectively. The precision of the NK and CG was such that only 56.25% and 62.5% of estimations, respectively, fell within 20% of TcGFR. In this study, the MDRD equation demonstrated the best overall performance among the 3 tested methods. It should be sufficient for routine clinical practice in kidney transplantation.