title: Kinetics of 14carbon dioxide excretion from 14C-urea by oral commensal flora.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Biophysics, Postgraduate Institute of Medical Education and Research, Chandigarh, India. chander_pathak@rediffmail.com
authors.forename: Chander M
authors.initials: CM
authors.lastname: Pathak
authors.forename: Pramod K
authors.initials: PK
authors.lastname: Avti
authors.forename: Deepak
authors.initials: D
authors.lastname: Bunger
authors.forename: Krishan L
authors.initials: KL
authors.lastname: Khanduja
mesh_terms: D000328:Adult; D000891:Anti-Infective Agents, Local / Q000008:administration & dosage; D001558:Benzethonium / Q000008:administration & dosage; D001944:Breath Tests; D002245:Carbon Dioxide / Q000378:metabolism*; D002250:Carbon Radioisotopes; D045853:Exhalation; D005260:Female; D016481:Helicobacter Infections / Q000175:diagnosis* / Q000382:microbiology; D016480:Helicobacter pylori / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D009055:Mouth / Q000382:microbiology*; D009067:Mouthwashes / Q000008:administration & dosage; D011237:Predictive Value of Tests; D014508:Urea; D014510:Urease / Q000378:metabolism*; D055815:Young Adult
chemical_list: D000891:Anti-Infective Agents, Local; D002250:Carbon Radioisotopes; D009067:Mouthwashes; D002245:Carbon Dioxide; D001558:Benzethonium; D014508:Urea; D014510:Urease