Is there an antigenic test for Helicobacter pylori (H. pylori)?

H. pylori Antigen Testing: Diagnostic Options

Yes, stool antigen testing is an effective non-invasive diagnostic test for H. pylori infection with high accuracy comparable to the urea breath test. 1

Available H. pylori Diagnostic Tests

Non-invasive Tests for Active Infection

1. Stool Antigen Test (SAT)

   • Laboratory-based monoclonal antibody tests have sensitivity of 94% and specificity of 92% 2
   • Equivalent accuracy to urea breath test when validated laboratory-based monoclonal tests are used 1
   • Requires proper laboratory processing and an acorn-sized stool sample 1
   • Available in two formats:
     • Laboratory ELISA tests (recommended)
     • Rapid in-office immunochromatographic tests (limited accuracy) 1

2. Urea Breath Test (UBT)

   • Gold standard non-invasive test with sensitivity 88-95% and specificity 95-100% 2
   • Requires patient to drink labeled urea solution which is metabolized by H. pylori 1

3. Serology Tests

   • Detect antibodies against H. pylori (IgG)
   • Cannot distinguish between active infection and past exposure 1
   • Remain positive long after infection eradication (serologic "scar") 1
   • Not recommended for confirming eradication 1, 2

Invasive Tests (Requiring Endoscopy)

• Rapid urease test
• Histology with special stains
• Culture
• Molecular testing

Important Considerations for Stool Antigen Testing

Test Accuracy Factors

• Medication interference:

  • PPIs should be stopped for at least 2 weeks before testing 1
  • Antibiotics and bismuth compounds should be stopped for at least 4 weeks 1, 2
  • H2-receptor antagonists do not affect bacterial load and don't need to be discontinued 1

• Test timing:

  • For initial diagnosis: can be performed at any time if medications are properly discontinued
  • For post-treatment confirmation: should be performed at least 4 weeks after completion of eradication therapy 2, 3

Special Clinical Situations

• Bleeding peptic ulcers: Stool antigen test has lower accuracy in patients with bleeding ulcers (sensitivity 82%, specificity 68%) compared to non-bleeding patients (sensitivity 93%, specificity 93%) 4

• Pediatric patients: Stool antigen testing is reliable in children with reported sensitivity of 91.3% and specificity of 97% 5

Recommendations for Clinical Practice

1. For initial diagnosis:

   • Use laboratory-based monoclonal stool antigen test or urea breath test 1
   • Ensure proper medication discontinuation before testing (PPIs for 2 weeks, antibiotics for 4 weeks) 1

2. For post-eradication confirmation:

   • Wait at least 4 weeks after completion of therapy 2, 3
   • Use stool antigen test or urea breath test, not serology 1, 2

3. Test selection based on availability and patient factors:

   • Both stool antigen test and urea breath test are appropriate for primary care use 1
   • Consider patient preference, local availability, and cost 1
   • For patients with bleeding ulcers, consider alternative testing methods due to reduced accuracy of stool antigen testing 4

The stool antigen test represents a practical, non-invasive method for diagnosing H. pylori infection when properly performed with validated laboratory-based monoclonal tests.