Enzymatic assay for creatinine with fixed-time kinetics on a centrifugal analyzer

A method is described for enzymatic measurement of serum creatinine using a centrifugal analyzer. The method employs fixed-time kinetics and a true serum blank. The method required 100 microliters of serum and is linear to 90 mg per L. Day-to-day precision studies revealed a standard deviation (coefficient of variation) of less than +/- 0.5 mg per L (7.4 percent) at a mean creatinine concentration of 6 mg per L and +/- 0.5 mg per L (1.8 percent) at a mean value of 28 mg per L. The method was free of interferences from acetoacetic acid, ascorbic acid, bilirubin, and hemoglobin. The speed, precision, and accuracy of the method suggest that it represents a useful alternative to methods using the alkaline picrate procedure.