Reagent for the in vitro quantitative determination of potassium in human serum for the control of electrolyte balance in the diagnosis and treatment of diseases characterized by high or low blood potassium levels. Potassium is determined spectrophotometrically by kinetic assay using potassium-dependent pyruvate kinase. The generated pyruvate is converted into lactate present in the conversion of NADH to NAD. The corresponding decrease in optical density at 380 nm is proportional to the potassium concentration in the serum.
