Urea, creatinine, and glucose determined in plasma and whole blood by a differential pH technique

We report the conditions (buffer composition and enzyme activity) required for estimating three frequently determined analytes--urea, glucose, and creatinine--by use of an improved version of the differential pH apparatus previously described (Clin Chem 29: 80-85, 1983). For each analyte, we used only one specific enzyme, thus avoiding a chain of auxiliary and indicator reactions. The method requires about a minute for each determination in undiluted plasma or whole blood.