Kinetics of 14carbon dioxide excretion from 14C-urea by oral commensal flora

Background and Aim: Previous studies have shown that while performing the 14C‐urea breath test (14C‐UBT) for the detection of Helicobacter pylori (H. pylori), there is possibility of false‐positive results due to the other urease producing bacteria present in oropharynx, if breath samples are obtained within 30 min after administration of non‐capsulated 14C‐urea. Therefore, we have exclusively evaluated the kinetics of 14carbon dioxide (14CO2) excretion by oral commensal flora to theoretically propose optimum breath collection timings for 14C‐UBT. Methods: Multiple breath samples up to 15 min were collected in 0.25 mmol benzethonium hydroxide from 25 healthy volunteers after they withheld 37 kBq (1 μCi) of 14C‐urea in their mouths for 15 s and then expectorated the tracer. The test was repeated on the same subjects without and with mouth cleansing protocols. Breath 14CO2 content was measured by the Liquid Scintillation Counter (1409; Wallac, Turku, Finland) and results were expressed as 14CO2 excretion per mmol breath CO2 (% administered dose). Results: Peak breath radioactivity at 1 min in the former protocol was 3.53 times higher than the latter which declined subsequently with a half time of 1 min and 2.5 min, and reached baseline levels by 15 and 10 min, respectively. The peak radioactivity (100%) at 1 min declined by 94% and 97.8% in the former and later protocols, respectively, at 15 min. Although magnitude of the peak varied in different subjects, the shape of curve remained almost similar in all cases. Conclusions: Without mouth cleansing, oral micro flora excreted more 14CO2 up to 15 min after administration of non‐capsulated 14C‐urea. Therefore, it is proposed that two breath samples may be obtained either at 15 and 20 min without or at 10 and 15 min with mouth cleansing protocols for reliable analysis of 14C‐UBT data for H. pylori detection.