What are the methods for diagnosing H. pylori infection?

Methods for Diagnosing Helicobacter pylori Infection

H. pylori infection can be diagnosed through both invasive and non-invasive methods, with the urea breath test (UBT) and stool antigen test (SAT) being the preferred non-invasive diagnostic approaches due to their high accuracy. 1, 2

Non-Invasive Diagnostic Tests

1. Urea Breath Test (UBT)

• Sensitivity and specificity: 94.7% and 95.7% respectively 2
• Mechanism: Patient ingests labeled urea which is hydrolyzed by H. pylori's urease enzyme, producing labeled CO2 that can be detected in breath
• Advantages: High accuracy, rapid results
• Limitations: False negatives with recent PPI use, antibiotics, or bismuth (should be stopped 2 weeks before testing) 1

2. Stool Antigen Test (SAT)

• Sensitivity and specificity: 88.8-92.1% and 87.3-87.6% respectively 2
• Types:
  • Laboratory-based monoclonal antibody tests (preferred) 1
  • Rapid in-office immunochromatographic tests (less accurate) 1
• Limitations: Similar to UBT regarding medication interference 1

3. Serological Tests

• Types: ELISA for anti-H. pylori IgG antibodies
• Advantages: Not affected by PPI use, antibiotics, or low bacterial load 1
• Limitations:
  • Cannot differentiate between active and past infection 1, 2
  • Accuracy varies between commercial kits (sensitivity 85%, specificity 79%) 1
  • Remains positive for months/years after eradication 1
• Best use case: When patient is on PPIs that cannot be stopped or in cases of bleeding, atrophy, or gastric malignancies 1

Invasive Diagnostic Tests (Requiring Endoscopy)

1. Histology

• Procedure: Examination of gastric biopsies
• Sensitivity/specificity: 90-95% sensitivity, 95-98% specificity 1
• Staining methods:
  • Modified Giemsa (recommended for routine use - sensitive, cheap, reproducible) 1
  • Immunohistochemistry (gold standard but more expensive) 1
  • Other options: Warthin-Starry, Gimenez, Genta stains 1
• Best practice: Take at least two samples each from antrum and body 1

2. Rapid Urease Test (RUT)

• Sensitivity/specificity: 80-95% sensitivity, 95-100% specificity 1
• Mechanism: Detects urease enzyme activity in biopsy specimens
• Advantages: Quick results (within hours), inexpensive
• Limitations:
  • Requires at least 10⁴ organisms for positive result 1
  • Low sensitivity post-treatment and in bleeding patients 1
  • False negatives with PPI use 1

3. Culture

• Advantages:
  • Definitive proof of infection 1
  • Allows antimicrobial susceptibility testing 1
• Limitations:
  • Technically demanding 1
  • Variable recovery rates between laboratories 1
  • Requires special transport conditions 1
• Indications: Recommended before first-line treatment in high clarithromycin resistance regions and after failed second-line treatment 1

4. Molecular Tests

• Can detect H. pylori and antibiotic resistance (clarithromycin/fluoroquinolone) directly from biopsies 1
• Useful when standard susceptibility testing isn't possible 1

Important Clinical Considerations

Pre-Test Preparation

• PPI discontinuation: Stop PPIs for 2 weeks before testing (UBT, SAT, RUT, culture, histology) 1
• Antibiotics and bismuth: Should be stopped at least 4 weeks before testing 1
• H2-receptor antagonists: Less interference than PPIs; can continue if using citric acid with UBT 1

Test Selection Algorithm

1. For patients <45 years without alarm symptoms:

   • Use non-invasive testing (UBT or SAT) 2

2. For patients with alarm symptoms or >45 years:

   • Refer for endoscopy with biopsy 2
   • Alarm symptoms include: bleeding, weight loss, dysphagia, palpable mass, anemia

3. For patients on PPIs who cannot stop:

   • Use validated IgG serology 1

4. After failed treatment:

   • Culture with susceptibility testing is recommended 1, 3

Common Pitfalls to Avoid

• Relying solely on serology for treatment decisions without confirming active infection 1
• Testing too soon after antibiotic or PPI therapy (leads to false negatives) 1
• Using rapid in-office stool tests instead of laboratory-based monoclonal antibody tests 1
• Taking insufficient biopsy samples during endoscopy 1
• Failing to perform post-treatment confirmation of eradication 2

By following these evidence-based approaches to H. pylori diagnosis, clinicians can accurately identify infections and appropriately guide treatment decisions to reduce morbidity and mortality associated with H. pylori-related diseases.