Abstract: The present invention provides a method for measuring dissolved inorganic carbon (DIC) in body fluids. The method can be used to measure DIC in blood, serum, plasma, urine, sweat, saliva, lacrimal fluid, and combinations thereof. The method can be used to diagnose a gastrointestinal disorder in a subject, and particularly a gastrointestinal disorder mediated by a urease producing bacterium such as Helicobacter priori.