Glucose Interference in Serum and Urine Samples with Various Creatinine Concentrations Measured by the Jaffe Kinetic Method.

Background: The effect of glucose interference on creatinine measurement by Jaffe kinetic method differs between serum and urine specimens. We investigated the effects of creatinine concentration and specimen dilution on glucose interference with urine creatinine measurement. Methods: Leftover serum and urine specimens were collected and stored at -20°C until study. Serum specimens were mixed to make 5 glucose concentrations ranging from <5.6 to 27.8 mmol/L, each group consisting of 5 levels of creatinine concentration ranging from <45 to 354 µmol/L. Urine specimens were divided into 5 groups of creatinine concentration ranging from <1,769 to >7956 µmol/L, each sample was spiked with glucose powder to produce 5 aliquots with glucose concentrations ranging from 0 to 666 mmol/L. Urine samples were automatically diluted 1:20 before analysis. Percent interference of creatinine measurement by Jaffe kinetic method was calculated using enzymatic method as the reference. Results: A total of 148 serum samples and 335 urine samples were analyzed. In serum, glucose interference with Jaffe creatinine measurement was found if creatinine concentrations were 177 µmol/L or less, corresponding to 3,540 µmol/L or less in urine specimens prior to 1:20 dilution. The degree of interference was greater when glucose concentration was higher or creatinine concentration was lower. Conclusions: When creatinine concentration and specimen dilution were considered, the effects of glucose interference on Jaffe creatinine measurement were similar in serum and urine specimens, and was found when creatinine concentrations in serum or diluted urine were 177 µmol/L or less.