Urea C-13
Urea 13C is a urea molecule radiolabelled with the non-radioactive element carbon-13. It is currently used for the Urea Breath Test (UBT) and is available as a rapid diagnostic test (marketed as Pranactin-Citric) for the detection of Helicobacter pylori infections. H pylori is a common stomach bacteria that has been linked to a variety of upper gastrointestinal disorders such as gastritis, gastric and peptic ulcers, stomach cancer, and gastric mucosa-associated lymphoid-tissue (MALT) lymphoma. The UBT is indicated to confirm H. pylori infection and to monitor post-treatment for its eradication.   Radiolabelled urea is available in two forms as 13C and 14C. Both forms can be used within the Urea Breath Test, however some may prefer 13C as it is non-radioactive compared to 14C, which may be preferable in pregnant women and children.  The Urea Breath Test is based on the ability of the H. pylori enzyme urease to cleave urea into ammonia and carbon dioxide. As the urease enzyme is not present in mammalian cells, the presence of urease (and the products of urea cleavage) in the stomach is evidence that H. pylori bacteria are present.  To detect H. pylori, urea labeled with 13C is swallowed by the patient. If gastric urease from H. pylori is present, urea is split to form CO2 and NH3 at the interface between the gastric epithelium and lumen and 13CO2 is absorbed into the blood and exhaled in the breath. Exhaled breath samples can then be collected and measured for the presence of radioactivity.