Effect of concomitant O-18 in C-13-urea on the urea breath test

Helicobacter pylori infection in stomach has been extensively assessed by t he C-13-urea breath test(UBT) with infra-red or mass spectrometer. However, analyses of commercially available C-13-urea for UBT showed about 10 atom% of O-18 abundance. It is therefore very important to investigate the O-18- isotope effect on UBT. Using a mass spectrometer, breath samples of UBT wer e analyzed to investigate the change of mass spectra by the isotopic exchan ge reaction between O-18 of carbon dioxide and O-16 of water. As the result , the O-18 content of C-13, O-18-carbon dioxide exhaled in UBT reached its natural abundance level inmediately after the administration of C-13, O-18- urea. It was concluded that the O-18 content of C-13, O-18-urea has no effe ct on UBT using either infra-red or mass spectroscopy.