Most methods for determining creatinine are based on the Jaffe reaction.1 In this reaction, creatinine interacts with alkaline picrate to form a reddish-yellow solution that is measured photometrically. This method is non-specific for urine creatinine, because other substances in urine also react with alkaline picrate. The Sciteck’s creatinine assay is a modified Jaffe method, with improved specificity over the original Jaffe procedure. Creatinine measurements are used in the diagnosis and treatment of renal diseases and in monitoring renal dialysis. The creatinine results are also used as a calculation basis for measuring other urine analytes. Urine creatinine values, as well as appearance and specific gravity are useful as an adjunct in detecting adulteration of urine samples submitted for drugs-of-abuse testing.