Evaluation of serum creatinine measurement by the direct acidification method for errors contributed by non-creatinine chromogens.

Serum creatinine determination by the direct acidification method was found to be non-specific. Chromogens other than creatinine could react with alkaline picrate and their developed color was also destroyed by acid. Only elevated levels of bilirubin and acetoacetate caused a significant interfering effect. The degree of this interference depended on: (1) the amount of the interfering substance; (2) the reaction time allowed for color development; and (3) the final acidity for decolorization.