C-13 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 the se tests the appearance in breath of a metabolite of a specific test s ubstance is studied. The assumption underlying each BT is that one ste p-the process of interest-in the absorption and metabolism of the trac er is rate-limiting. Both hydrogen gas excretion and carbon dioxide ap pearance in breath can be studied. When a carbon-labelled test substan ce is used, the stable isotope C-13 is preferred to the radioactive is otope C-14. Measurements of C-13 in expired air are performed by mass spectrometry. Because of the indirect nature of BTs, involving a seque nce of reactions and metabolic pools, they usually supply semiquantita tive data. The tests are nevertheless useful because they often replac e invasive techniques with a simple procedure that is safe because the re is no radioactivity involved. BTs have been used to measure gastric emptying, the presence of Helicobacter pylori in the stomach, small-b ower bacterial overgrowth, exocrine pancreatic function as well as liv er metabolic capacity; other potential applications of BTs are being s tudied.