A urea breath test checks for Helicobacter pylori, usually called H. pylori, in the stomach. It can help find an infection or check whether treatment has cleared it. The test uses breath samples before and after swallowing a test substance.
H. pylori can break down urea into carbon dioxide. In a 13C test, the urea contains a form of carbon that the laboratory can recognise. If the bacteria break it down, some of that carbon appears in the air you breathe out.
The laboratory compares samples taken before and after the urea. The test looks for this sign of bacterial activity. It is different from a blood antibody test, which may remain positive after an earlier infection.
Some medicines, including antibiotics and acid-suppressing medicines, can affect testing. Tell the service which medicines you take and follow its instructions about food, drink and any planned medicine pause. Do not stop prescribed treatment on your own.
A positive result usually indicates an H. pylori infection. A negative result makes infection less likely, but ongoing symptoms may need other tests. If this is a check after treatment, the timing must also follow the instructions from your clinician.

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