H. pylori breath test. Box containing the Pylobactell 13-C urea breath test kit to diagnose gastroduodenal Helicobacter pylori infection. Next to the box is a carton of orange juice, which is taken before the test to prevent gastric (stomach) emptying. At the start of the test the patient breathes out into a sealed tube to give a before sample. They then drink a solution of 13C-urea, a compound containing a rare stable isotope of carbon (13C). Any H. pylori bacteria present will metabolise this urea, creating 13C labelled carbon dioxide as a waste product, which will be detected in the post sample breath test. H. pylori is a bacterium commonly found in the mucus lining of the stomach. It causes gastritis and is also the most common cause of stomach ulcers.