Factors for False Positive H. pylori Breath Test Results
False positive urea breath test results are rare, with the primary cause being achlorhydria or atrophic gastritis allowing urease-producing non-H. pylori organisms to generate positive results. 1
Primary Cause of False Positives
- Achlorhydria or atrophic gastritis is the main mechanism for false positive breath tests, as these conditions allow other urease-producing bacteria (non-H. pylori organisms) to colonize the stomach and hydrolyze the labeled urea, mimicking H. pylori infection 1
Important Distinction: Medications Cause False Negatives, Not False Positives
- Proton pump inhibitors, antibiotics, and bismuth compounds cause false-negative results (10-40% rate), not false-positive results 2, 1, 3
- A positive breath test can be trusted even if the patient was recently on PPIs, antibiotics, or bismuth, because these medications suppress bacterial load rather than create spurious positive signals 2, 1
- This is a critical clinical point: if a patient on acid suppression has a positive breath test, the result is reliable and treatment can proceed 3
The Problem of "False Positives" in Low Prevalence Populations
- In populations with low H. pylori prevalence, the positive predictive value of any test decreases, making it statistically more likely that a positive result represents a false positive 2
- A single positive noninvasive test in low prevalence populations should be confirmed with a second test measuring a different parameter (e.g., positive UBT confirmed by stool antigen test) before initiating treatment 4
- Studies examining presumed "acute" H. pylori infections (positive UBT with negative serology) found that 80% (4 of 5 children) had negative follow-up UBTs, suggesting the initial positive was false 4
Technical and Procedural Factors
- Inadequate fasting (less than 6 hours) before the test may theoretically affect results, though this is primarily a concern for test accuracy rather than false positives specifically 1, 5
- Use of liquid formulations rather than tablet forms of ¹³C-urea can allow interference from urease-producing bacteria in the oropharynx, potentially causing false positives 1
- Failure to use a test meal or citric acid to delay gastric emptying may affect even distribution of labeled urea, though evidence suggests this may not significantly impact accuracy 1
Clinical Approach to Suspected False Positives
- When clinical suspicion for H. pylori is low but the breath test is positive, confirm with a second noninvasive test using a different methodology (stool antigen test if UBT was positive, or vice versa) 4
- In patients with known atrophic gastritis or achlorhydria, consider endoscopy with histology using immunohistochemistry as the gold standard rather than relying solely on breath testing 2, 3
- Serology remains positive long after eradication (a "serologic scar") and should not be used to confirm active infection, but can help distinguish true infection from false positive noninvasive tests 2, 3
Key Caveat
The urea breath test has excellent specificity (95-95.7%), meaning true false positives are uncommon 2, 1, 5. Most apparent "false positives" in clinical practice are either true positives in patients with low pretest probability, or represent the statistical reality of testing in low prevalence populations rather than actual test failure 2, 4.