How to Perform a Urea Breath Test
The urea breath test requires the patient to fast for at least 6 hours, provide a baseline breath sample, ingest isotopically-labeled urea (either ¹³C or ¹⁴C) with a test meal, and then provide a second breath sample 10-30 minutes later for analysis. 1
Pre-Test Patient Preparation
Medication Discontinuation
- Stop proton pump inhibitors (PPIs) for at least 2 weeks before testing to avoid false-negative results, as PPIs reduce bacterial load and cause 10-40% false-negative rates 2, 3
- Discontinue antibiotics and bismuth compounds for at least 4 weeks prior to testing, as these medications temporarily suppress H. pylori and produce false-negative results 2, 3
- H2-receptor antagonists do not significantly affect test accuracy and can be substituted for PPIs during the waiting period 3
Fasting Requirements
- Patients must fast for at least 6 hours before the test 1
- However, evidence suggests that a light breakfast (two slices of toast with jam or honey and tea or coffee) does not reduce test accuracy, with 98% sensitivity and 96% specificity maintained in non-fasting conditions 4
Test Procedure
Step 1: Baseline Breath Sample
- Collect an initial breath sample before administering labeled urea 2, 5
- This baseline sample accounts for endogenous CO₂ production 2
- Samples collected within the first 5 minutes should be discounted as they may contain urease from oral bacteria 6
Step 2: Urea Administration
- Administer 75 mg of ¹³C-labeled urea (or 37-185 kBq of ¹⁴C-urea if using the radioactive version) 2
- The ¹³C version is strongly preferred as it is non-radioactive and safe for children and pregnant women 5, 7
- Give the labeled urea with a test meal to delay gastric emptying and allow even distribution throughout the stomach 2
- Tablet formulations of ¹³C-urea are superior to liquid forms as they avoid interference from urease-producing bacteria in the oropharynx 2
Step 3: Breath Sample Collection
- Collect the second breath sample 10-30 minutes after urea ingestion 2, 5
- Modern tablet formulations allow accurate sampling as early as 10 minutes post-ingestion 2
- Traditional protocols using liquid urea typically require sampling at 30 minutes 5
- The patient exhales into a collection device (CO₂-trapping agent for ¹⁴C or collection bag for ¹³C) 2
Step 4: Sample Analysis
- For ¹³C-urea: Analyze using isotope ratio mass spectrometry (IRMS), non-dispersive isotope-selective infrared spectroscopy (NDIRS), or laser-assisted ratio analysis (LARA) 5
- For ¹⁴C-urea: Measure radioactivity using a scintillation counter 2
- Results are expressed as percentage of administered dose adjusted for endogenous CO₂ production 2
Test Interpretation
Diagnostic Accuracy
- The UBT demonstrates excellent accuracy with sensitivity of 94.7-97% and specificity of 95-95.7% based on analysis of 3,643 patients 2, 1, 3
- This makes it superior to serological tests and comparable to stool antigen testing 1, 3
Understanding Results
- Positive results can be trusted even if the patient was on medications, as PPIs and antibiotics cause false-negatives, not false-positives 2
- False-positive results may occur in patients with achlorhydria or atrophic gastritis due to urease-producing non-H. pylori organisms 2, 8
- When false-positive tests are suspected, confirm with stool antigen testing or endoscopy before initiating treatment 2
Common Pitfalls and How to Avoid Them
Medication Interference
- The most common cause of false-negative results is inadequate washout of PPIs, antibiotics, or bismuth 2, 3
- If testing cannot be delayed, a positive result remains valid despite recent medication use 2
- When in doubt about a false-negative result, repeat testing after at least 2 weeks off interfering medications 2
Post-Treatment Testing
- Wait 4-6 weeks after completing eradication therapy before performing UBT to confirm successful treatment 9
- Testing too early may yield false-negative results even if treatment failed 9