A kinetic and enzymatic method for determination of creatinine in serum and urine

Abstract

Creatinine amidohydrolase was used to determine creatinine in a totally enzymatic procedure. Creatine was produced by hydrolysis of creatinine, and coupled with creatine kinase, pyruvate kinase and lactate dehydrogenase to result in a change in absorbance at 340 nm. Results of studies on each reaction rate in the enzymatic reaction sequence were discussed. The relationship between creatinine concentration and absorbance at 340 nm was linear up to a creatinine concentration of at least 20mg/dl.
Glucose, uric acid, urea, bilirubin and arginine were without significant effects on the accurate determination of creatinine at the concentrations employed. The addition of significantly higher concentrations of ascorbic acid and hemoglobin slightly inhibited the activity of the reaction sequence.
When results of this procedure and of the standard direct Jaffe test were compared using seru mand urine samples, the correlation coefficient was 0.984, but the former were slightly higher. Unlike the Jaffe method, the present method of determining creatinine is rapid, subject to few interfering substances, and requires no serum deproteinization.