What is the recommended treatment and follow-up for H. pylori infection diagnosed by stool antigen test?

H. Pylori Stool Antigen Test: Diagnostic Performance and Clinical Application

The stool antigen test is a highly accurate, non-invasive method for diagnosing active H. pylori infection with sensitivity and specificity of 93.2%, and should be used with validated laboratory-based monoclonal antibody tests rather than rapid in-office versions. 1

Diagnostic Accuracy

The stool antigen test demonstrates excellent performance characteristics that make it equivalent to the urea breath test (UBT):

• Pre-treatment diagnosis: Sensitivity 93.2% and specificity 93.2% based on evaluation of 3,419 patients 1
• Post-treatment confirmation: Sensitivity 92.1% and specificity 87.6% when using proper gold standards 1
• The European Helicobacter Pylori Study Group formally recommends using either UBT or stool antigen testing for initial diagnosis 1

Critical distinction: Only laboratory-based monoclonal antibody tests achieve this accuracy—rapid in-office immunochromatographic tests have significantly lower accuracy and should be avoided 1, 2

When to Use Stool Antigen Testing

Primary Indications

• Initial diagnosis in patients <50 years with uninvestigated dyspepsia and no alarm symptoms as part of "test and treat" strategy 3, 2
• Confirmation of eradication after treatment (wait at least 4 weeks post-therapy) 1, 3, 2
• Alternative to UBT when breath testing is unavailable or impractical 1

When NOT to Use (Proceed Directly to Endoscopy)

• Patients ≥50 years with new-onset dyspepsia (increased malignancy risk) 3, 2
• Any patient with alarm symptoms: bleeding, weight loss, dysphagia, palpable mass, or malabsorption 3, 2
• Patients who failed eradication therapy and need culture/susceptibility testing 2

Critical Pre-Test Requirements

Medication washout periods are essential to avoid false-negative results:

• Stop proton pump inhibitors (PPIs): At least 2 weeks before testing 1, 3, 2
• Stop antibiotics and bismuth: At least 4 weeks before testing 1, 3, 2
• PPIs can cause false-negative results in up to 40% of patients by reducing bacterial load 1

Common pitfall: Testing too soon after medication use is a frequent cause of false-negative results 1

Post-Treatment Confirmation

• Timing: Perform testing at least 4 weeks after completing eradication therapy 1, 3, 2
• Never use serology for post-treatment confirmation—antibodies persist long after eradication 2
• Monoclonal antibody-based stool tests show sensitivity of 91.6% and specificity of 98.4% for post-treatment assessment 4

Advantages Over Alternative Tests

• Detects active infection only (unlike serology which cannot distinguish current from past infection) 3, 2
• More practical than endoscopy: Avoids procedure-related discomfort, expense, and complications 3
• Safe in all populations: Can be used in children and pregnant women (unlike radioactive 14C-UBT) 1
• Cost-effective: Less expensive than UBT while maintaining comparable accuracy 5

Test Selection Algorithm

For initial diagnosis:

1. Patient <50 years without alarm symptoms → Use validated monoclonal stool antigen test OR UBT 1, 3, 2
2. Patient recently used PPIs/antibiotics → Either wait 2-4 weeks for washout, or consider validated IgG serology 1, 2
3. Patient ≥50 years or with alarm symptoms → Endoscopy with biopsy-based testing 3, 2

For post-treatment confirmation:

1. Wait minimum 4 weeks after completing therapy 1, 3, 2
2. Ensure proper medication washout (PPIs 2 weeks, antibiotics 4 weeks) 1, 3, 2
3. Use monoclonal stool antigen test OR UBT—never serology 1, 3, 2

Important Caveats

• Stool consistency matters: Accuracy decreases with unformed or watery stools due to antigen dilution 5
• Temperature and timing: Storage conditions and interval between collection and testing affect results 5
• Test kit selection: Choose validated monoclonal antibody-based laboratory tests, not rapid office tests 1, 2
• False negatives at end of therapy: All patients may test negative immediately after completing treatment, even if eradication failed—this is why 4-week delay is mandatory 6

Treatment Following Positive Test

When stool antigen test confirms H. pylori infection, standard eradication therapy includes:

• Triple therapy: Amoxicillin 1 gram + clarithromycin 500 mg + lansoprazole 30 mg, all twice daily for 14 days 7
• Dual therapy alternative: Amoxicillin 1 gram + lansoprazole 30 mg, both three times daily for 14 days 7