13C breath tests in gastroenterological practice

Breath tests (BTs) are used in gastroenterological practice to study (patho)physiologicaI and metabolic processes in an indirect way. In these tests the appearance in breath of a metabolite of a specific test substance is studied. The assumption underlying each BT is that one step-the process of interest-in the absorption and metabolism of the tracer is rate-limiting. Both hydrogen gas excretion and carbon dioxide appearance in breath can be studied. When a carbon-labelled test substance is used, the stable isotope C-13 is preferred to the radioactive isotope C-14. Measurements of C-13 in expired air are performed by mass spectrometry. Because of the indirect nature of BTs, involving a sequence of reactions and metabolic pools, they usually supply semiquantitative data. The tests are nevertheless useful because they often replace invasive techniques with a simple procedure that is safe because there is no radioactivity involved. BTs have been used to measure gastric emptying, the presence of Helicobacter pylori in the stomach, small-bower bacterial overgrowth, exocrine pancreatic function as well as liver metabolic capacity; other potential applications of BTs are being studied.