Urea breath test (UBT): The urea breath test (UBT) is a procedure for diagnosing the presence of a bacterium, Helicobacter pylori (H. pylori) that causes inflammation, ulcers, and atrophy of the stomach. The test also may be used to demonstrate that H. pylori has been eliminated by treatment with antibiotics.

The urea breath test is based on the ability of H. pylori to break down urea, a chemical made of nitrogen and carbon, that normally is produced by the body from excess ("waste") nitrogen and then eliminated in the urine. For the test, patients swallow a capsule containing urea made from an isotope of carbon. (Isotopes of carbon occur in minuscule amounts in nature, and can be measured with special testing machines.) If H. pylori is present in the stomach, the urea is broken up into nitrogen and carbon (as carbon dioxide). The carbon dioxide is absorbed across the lining of the stomach and into the blood. It then is excreted from the lungs in the breath. Samples of exhaled breath are collected, and the isotopic carbon in the exhaled carbon dioxide is measured.

If the isotope is detected in the breath, it means that H. pylori is present in the stomach. If the isotope is not found, H. pylori is not present. When the H. pylori is effectively treated (eradicated) by antibiotics, the test changes from positive (isotope present) to negative (isotope absent).