Kinetic approach for the enzymic determination of creatinine.

By exploiting the kinetics of NADH consumption in the enzyme system creatinine amidohydrolase + creatine kinase + pyruvate kinase + lactate dehydrogenase, one can determine creatinine in serum in the range of 1 to 90 mg/L. By using the conditions defined here, this determination can be made with a single measurement of the rate of disappearance of NADH. The analytical rate measurement is made at a fixed time (2 min) after the sample is introduced into the enzyme solution. For this fixed time, the interferences of creatine and pyruvate are eliminated. Results so obtained for creatinine in human blood serum samples correlated well (r = 0.98) with those obtained by the classical Jaffé-reaction method. Run-to-run reproducibility (CV) was 3%, and the limit of detection was 1 mg/L.