A new method is described for determing creatine in serum and urine. The method consists of two steps of reaction: The first step is conversion of phosphoenol-pyruvate to pyruvate in the presence of creatine, creatine-phosphokinase, pyruvate kin-ase and ATP. The second step is a reaction of pyruvate with hydrazine, forming hydrazone which shows the maximum absorbance at 450nm under the alkaline condition.
The method is more specific for creatine determination compared with Jaffe method which is widely employed in clinical laboratory test judging from the results concerned with substances interfering with the reaction. In addition, it is highly reproducible, and the coefficients of variation were 5.1 and 2.1%, respectively, when two samples containing 1.3 and 7.2mg/100ml of creatine are assayed.
Furthermore, the method is fairly simple and rapid to perform, so that it is considered to be suitable for the clinical purposes.
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