Abstract: A non-invasive method for the functional assessment of an inherited metabolic disorder in infants and children including administering to the patient a predetermined substrate labeled with a stable non-radioactive isotope of carbon .sup.13 C, analyzing the breath samples for the isotopic abundance of .sup.13 CO.sub.2, and calculating the quantity of substrate oxidized for determining the rate of substrate oxidation.

Abstract: A drink adapted to be consumed by a patient to enable measurement of gastric emptying of the liquid phase, is a fruit juice having mixed and suspended therein a quantity of Spirulina platensis alga grown in a .sup.13 CO.sub.2 atmosphere. These single cell organisms pass from the stomach into the small intestine where they are digested, absorbed and oxidized to produce a detectible rise in the level of .sup.13 CO.sub.2 in the patient's breath which is sampled and the measured valves plotted to enable determination of gastric emptying rate abnormalities.

Abstract: A biscuit adapted to be ingested by a patient to enable measurement of gastric emptying has added prior to baking Spirulina Platensis alga grown in a .sup.13 CO.sub.2 atmosphere. These single cell organisms are oxidized after digestion in the small intestine to produce a detectible rise in level of .sup.13 CO.sub.2 in the patient's breath which is sampled and plotted to enable diagnosis of abnormal gastric emptying rates.