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

Background And Aim: Previous studies have shown that while performing the (14)C-urea breath test ((14)C-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 (14)C-urea. Therefore, we have exclusively evaluated the kinetics of (14)carbon dioxide ((14)CO(2)) excretion by oral commensal flora to theoretically propose optimum breath collection timings for (14)C-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 muCi) of (14)C-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 (14)CO(2) content was measured by the Liquid Scintillation Counter (1409; Wallac, Turku, Finland) and results were expressed as (14)CO(2) excretion per mmol breath CO(2) (% 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 (14)CO(2) up to 15 min after administration of non-capsulated (14)C-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 (14)C-UBT data for H. pylori detection.