Creatinine concentration in plasma from dog, rat, and mouse: a comparison of 3 different methods

Background: There are numerous methods for analyzing creatinine concentration in plasma, including the Jaffe alkaline picrate method in various modifications, enzymatic tests, and chromatographic methods. Objective: The purpose of this study was to evaluate whether an enzymatic method could replace a Jaffe method for routine creatinine measurements in plasma from dogs, rats, and mice. The enzymatic method and a compensated Jaffe method were tested against a high-pressure liquid chromatography (HPLC) method, regarded as the gold standard for creatinine measurement. Methods: Heparinized plasma samples were obtained from 20 beagle dogs, 20 Wistar rats, and 20 CD1-strain mice. The 2 test kits (Roche Diagnostics), Creatinine Jaffe Compensated and the enzymatic Creatinine Plus Version 2 reagent, were used on a Cobas Integra 400. The Jaffe compensated method used a calibration adjustment of-18 mu mol/L to correct for the protein matrix in serum and plasma. The HPLC method was an isocratic method using a weak cation-exchange column following protein precipitation. Results: Creatinine concentrations obtained using the enzymatic and the Jaffe methods differed significantly from the results obtained by the HPLC method. For dog plasma, mean values of 61.2, 61.8, and 67.8 mu mol/L were obtained by the compensated Jaffe, enzymatic, and HPLC methods, respectively. In the rat, respective mean values were 26.7, 21.9, and 23.0 mu mol/L, and in the mouse, respective mean values were 14.2, 5.4, and 9.2 mu mol/L. Conclusion: The enzymatic method can replace the Jaffe method for plasma creatinine determination in dogs, rats, and mice because results from the enzymatic method were closer to HPLC values than were those of the Jaffe method.