Breath tests

Just as oxygen spreads from the lungs into the entire body when you breathe in, so when you breathe out there are many substances in the air that are excreted from the organism in this way. Some can be detected in the breath test and allow conclusions to be drawn about certain functional disorders, especially in the stomach and small intestine.

The principle

Breath tests take advantage of the fact that bacteria present in the gastrointestinal tract break down substances. The resulting products enter the bloodstream and from there into the lungs, where they are exhaled and can thus be measured. There are two groups of tests:

  • C breath tests:  The 13C breath test measures the concentration of carbon dioxide, which is produced, among other things, when urea is split. The urea is labeled 13C and is taken orally. In the stomach, it is broken down by urease, an enzyme of the bacterium  Helicobacter pylori  (which  causes gastric ulcers  ), and then absorbed. This is how it gets into the body. The increase in the marked carbon dioxide (13CO2) then contained in the exhaled air is measured. For special questions, the C breath tests are also carried out with marker substances other than urea (13C octanoic acid, 13C sodium acetate or 14C glycocholate).
  • H2 breath test:  This measures the concentration of hydrogen (H2), a product of the breakdown of  carbohydrates  in the intestine. Depending on which function is to be examined, a test substance with a specific sugar is administered. Lactose, sucrose, glucose,  fructose , xylose or lactulose are given.

Pros and cons of breath testing

  • Breath tests have the advantage that they are safe and not very stressful for the patient – they can therefore even be carried out on children. The H2 breath tests in particular are very accurate.
  • However, the patient’s active cooperation is required for the test to be meaningful. The patient must cooperate reliably and patiently both during the preparation (nutrition the day before, on an empty stomach) and during the examination.
  • A disadvantage is that the laboratories require a relatively large amount of equipment.
  • Many of the tests are inconclusive shortly after antibiotic therapy or after examinations that are associated with a colonic (e.g.  colonoscopy ) – so you have to wait a few weeks.


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