Specificity of Accepted Procedures for Urine Creatinine

Specificities of various commonly used procedures for creatinine in urine were evaluated after subjecting pure creatinine or urine (with or without added creatinine) to counter-current distribution (CCD) between acetate buffer (pH 4.6) and n-butanol. After 10 transfers, each phase of each tube was analyzed for creatinine by each of the various procedures, and the resulting data were compared with the theoretical distribution curve for pure creatinine. The data indicate that the original or automated Jaffé reaction is the most nearly specific of the procedures investigated. Thus, the CCD technique, besides being a powerful separatory tool, also permits a physicochemical approach to the evaluation of specificities of standard procedures in clinical chemistry.