Inaccuracy of routine creatinine measurement in canine urine

Background: Urine creatinine concentration often is used in ratios such as urine protein:creatinine to compensate for dilution or concentration of spot urine samples. Objective: The purpose of this study was to compare the accuracy of different techniques of urine creatinine measurement currently available for veterinary practitioners. Methods: In 104 samples of canine urine diluted 1:20 with distilled water, creatinine concentration was measured using a kinetic Jaffe reaction assay, and an enzymatic technique on an automatic analyzer (Elimat) and 3 benchtop analyzers (Reflovet, Scil; Vitros DT2, Ortho-Clinical Diagnostics; Vettest 8008, IDEXX) used in veterinary practice. Results: The Jaffe and enzymatic techniques on the Elimat were not significantly different, and their inaccuracy tested with human control urines was <5%. The benchtop analyzers underestimated creatinine concentration, especially at concentrations >2000 mg/L. Inaccuracy was higher with multilayer slide technology systems (Vitros and Vettest) than with the Reflovet system. Results were approximately 25% and 2% lower, respectively, than with the Elimat at urine creatinine concentrations about 2000 mg/L. Conclusion: Inaccuracy in urine creatinine measurements using benchtop analyzers should be taken into account when defining decision thresholds, which should be corrected according to the method used to avoid misinterpretations. (C) 2004 American Society for Veterinary Clinical Pathology.