Breath tests in intestinal diseases and functional gastrointestinal diagnosis

Among the numerous breath tests described for gastroenterological applications, breath hydrogen (H2) tests have emerged during the past two decades as a most sensitive, reliable and feasible method for detecting carbohydrate malabsorption and maldigestion (e. g. lactose maldigestion). Hence they are regarded time honored standards of contemporary gastroenterological function tests. For the diagnosis of the small bowel bacterial overgrowth syndrome the glucose H2 breath test is a feasible tool with moderate sensitivity (approximately 65%), which, however, is not higher with alternative breath test (e. g. the 1 g 14C-D-xylose breath test). Measuring mouth-to-caecum-transit time by the breath H2 response after lactulose is more of scientific interest than clinically informative. Breath tests making use of 14C labeled substrates (usually 5 to 10 microCi) bear a rather low calculated radiation hazard and are thus in routine use in some countries, e. g. in Scandinavia, but they are abandoned in others. At least, however, radioactive 14C breath tests are (partially) dispensible, as these restrictions do not apply for the stable isotope 13C breath tests which are nonradioactive and thus devoid of any radiation hazard. For the purpose of gastroenterological function testing the 13C urea breath test for the detection of Helicobacter pylori infection, quantitative studies of gastric emptying with 13C-acetate or 13C-octanoate and quantitative liver function tests have gained diagnostic use while 13C-breath tests assessing intestinal absorption or exocrine pancreatic function have been found less effective than the respective alternatives, or too expensive. Both, H2-breath tests and 13CO2-breath tests are clinically important, diagnostic methods with well delineated indications in gastroenterology.