A 45-year-old diabetic presents with epigastric pain, early satiety, and a positive urea breath test (UBT). 13C-UBT is used for Helicobacter pylori detection. The principle of UBT is based on:
- A H. pylori produces 13CO2 directly from metabolism of 13C-bicarbonate in the gastric mucosa
- B H. pylori catalase reacts with labeled H2O2 to release 13CO2 in the stomach
- C H. pylori urease cleaves 13C-labeled urea to produce 13CO2, detected in exhaled breath by mass spectrometry ✓
- D Serum 13C-labeled urea concentration decreases as H. pylori absorbs it from the blood stream
Explanation
The 13C urea breath test exploits H. pylori's urease enzyme, which is its primary virulence factor for colonization (by generating ammonia from urea to neutralize gastric acid). In the UBT, the patient ingests 13C-labeled urea (a stable, non-radioactive isotope). H. pylori urease cleaves the labeled urea to 13CO2 and ammonia. The 13CO2 is absorbed into the bloodstream, transported to the lungs, and exhaled. Exhaled breath is collected and analyzed by mass spectrometry (or infrared spectroscopy) to detect the enriched 13CO2/12CO2 ratio. UBT has >95% sensitivity and specificity for active H. pylori infection and is a non-invasive test of cure. PPIs and antibiotics must be stopped 4 weeks before testing to avoid false negatives.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.