Dynamic carbon 13 breath tests for the study of liver function and gastric emptying

In gastroenterological practice, breath tests (BTs) are diagnostic tools used for indirect, non-invasive assessment of several pathophysiological metabolic processes, by monitoring the appearance in breath of a metabolite of a specific substrate. Labelled substrates originally employed radioactive carbon 14 (C-14) and, more recently, the stable carbon 13 isotope (C-13) has been introduced to label specific substrates. The ingested C-13-substrate is metabolized, and exhaled (CO2)-C-13 is measured by mass spectrometry or infrared spectroscopy. Some C-13-BTs evaluate specific (microsomal, cytosolic, and mitochondrial) hepatic metabolic pathways and can be employed in liver diseases (i.e. simple liver steatosis, non-alcoholic steato-hepatitis, liver fibrosis, cirrhosis, hepatocellular carcinoma, drug and alcohol effects). Another field of clinical application for C-13-BTs is the assessment of gastric emptying kinetics in response to liquids (C-13-acetate) or solids (C-13-octanoic acid in egg yolk or in a pre-packed muffin or the C-13-Spirulina platensis given with a meal or a biscuit). Studies have shown that C-13-BTs, used for gastric emptying studies, yield results that are comparable to scintigraphy and can be useful in detecting either delayed-(gastroparesis) or accelerated gastric emptying or changes of gastric kinetics due to pharmacological effects. Thus, C-13-BTs represent an indirect, cost-effective and easy method of evaluating dynamic liver function and gastric kinetics in health and disease, and several other potential applications are being studied.