H. pylori Diagnosis: Stool Antigen Testing
Optimal Diagnostic Approach
For initial diagnosis of H. pylori infection, use either the urea breath test (UBT) or laboratory-based monoclonal stool antigen test, both achieving approximately 93% sensitivity and specificity, with stool antigen testing being more practical and cost-effective than serology. 1, 2
Why Stool Antigen Testing is Preferred
The stool antigen test directly detects active H. pylori infection with 93.2% sensitivity and 93.2% specificity, unlike serology which cannot distinguish current from past infection and averages only 78% accuracy. 1, 2
Laboratory-based monoclonal antibody stool tests are significantly more accurate than rapid in-office immunochromatographic tests, which should be avoided entirely. 1, 2
The test detects bacterial antigens in stool specimens, making it safe for all populations including children and pregnant women, unlike the radioactive 14C-UBT. 1, 2
Critical Testing Requirements
Stop proton pump inhibitors for at least 2 weeks before testing, and discontinue antibiotics and bismuth for at least 4 weeks, as these medications cause 10-40% false-negative rates by reducing bacterial load. 1, 2
Histamine-2 receptor antagonists do not affect bacterial load and can substitute for PPIs when acid suppression is needed before testing. 1
For post-treatment confirmation of eradication, wait at least 4 weeks after completing therapy before performing stool antigen testing or UBT. 1, 2
When to Use Alternative Diagnostic Methods
Serology (Limited Role)
Validated IgG serology should only be used when patients have recently used antibiotics or PPIs and cannot wait the required washout period, or in cases of ulcer bleeding, atrophic gastritis, or gastric malignancies where other tests may be falsely negative. 1
Never use serology to confirm eradication after treatment, as antibodies remain elevated long after bacterial elimination. 1, 2
Endoscopy with Invasive Testing
Proceed directly to endoscopy in patients ≥50 years with new-onset dyspepsia, or any patient with alarm symptoms (bleeding, weight loss, dysphagia, anemia, palpable mass). 1, 2
Endoscopy with culture and susceptibility testing is essential after treatment failure, particularly in regions with high clarithromycin resistance (>15-20%). 1, 2
Rapid urease test during endoscopy provides results before the patient leaves the unit, with 80-95% sensitivity and 95-100% specificity. 2
Treatment Considerations with Penicillin Allergy
First-Line Options
In patients with documented penicillin allergy, bismuth quadruple therapy (PPI-bismuth-tetracycline-metronidazole) for 10-14 days achieves 74-75% eradication rates and should be the preferred first-line treatment. 3
Vonoprazan-clarithromycin-metronidazole demonstrates excellent eradication rates with better tolerability than bismuth quadruple therapy and may be considered first-line if accessible. 4
PPI-clarithromycin-metronidazole triple therapy achieves only 57-59% eradication rates and should be avoided as first-line therapy in penicillin-allergic patients. 5, 3
Rescue Options After Treatment Failure
Levofloxacin-based triple therapy (PPI-clarithromycin-levofloxacin) for 10 days achieves 64% eradication rates as second-line therapy, even after multiple treatment failures. 5, 3
Sitafloxacin-metronidazole-PPI triple therapy for 10 days achieves 89.5% eradication in penicillin-allergic patients, but fails in cases of double resistance to both antibiotics (40% success rate). 6
Rifabutin-based regimens (PPI-clarithromycin-rifabutin) should be avoided due to poor eradication rates (11-22%) and frequent serious adverse effects including myelotoxicity in 89% of patients. 5, 3
Verifying Penicillin Allergy
Patients with suspected non-severe, immediate-type penicillin allergy that occurred >5 years ago can receive cephalosporins with dissimilar side chains (such as cefazolin) without prior testing, as cross-reactivity risk is low. 7
Consider formal allergy testing in patients who have failed 2+ H. pylori treatment courses, as confirmed penicillin allergy would allow use of highly effective amoxicillin-based regimens. 8
Cefuroxime has been used as an alternative to amoxicillin in some H. pylori regimens, though evidence is limited. 4
Common Pitfalls to Avoid
Never use rapid in-office serological tests—they have inadequate accuracy (68-82%) for clinical decision-making. 1
Do not perform stool antigen testing while patients are taking PPIs, as this causes false-negative results in up to 40% of cases. 1, 2
Avoid polyclonal stool antigen tests for post-treatment confirmation, as specificity drops to 87.6% compared to 93-97% for monoclonal tests. 2
Do not assume all "penicillin allergies" are true allergies—many patients labeled as allergic can safely receive beta-lactams after appropriate evaluation. 7, 8