Just as oxygen spreads from the lungs throughout the body when inhaled, many substances are found in the air when exhaled and are eliminated from the body in this way. Some can be detected in the breath test and allow conclusions to be drawn about certain functional disorders, especially of the stomach and small intestine.
The principle
Breath tests make use of the fact that bacteria present in the gastrointestinal tract break down substances. The resulting products enter the bloodstream and from there to 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, one of the products of which is formed when urea is broken down. The urea is labeled 13C and is absorbed by mouth. In the stomach, it is broken down by urease, an enzyme produced by the bacterium Helicobacter pylori (which is present in gastric ulcers), and is subsequently absorbed. This is how it enters the body. The increase in labeled carbon dioxide (13CO2) then contained in exhaled air is measured. For special questions, the C-breath tests are also performed with other labeling substances 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. Given are lactose, sucrose, glucose, fructose, xylose or lactulose.
Advantages and disadvantages of breath tests
- Breath tests have the advantage that they are safe and not very stressful for the patient – therefore, they can be performed even in children. H2 breath tests in particular are very accurate.
- However, active cooperation of the patient is required for the test to be meaningful. Both in the preparation (diet the day before, fasting) and during the examination, the patient must reliably and patiently participate.
- A disadvantage is that a relatively high equipment expenditure is necessary for the laboratories.
- Many of the tests are not conclusive shortly after antibiotic therapy or after examinations that involve intestinal lavage (e.g. colonoscopy) – so it is necessary to wait a few weeks.
