What is the diagnostic and treatment approach for H. pylori (Helicobacter pylori) infection using the H. pylori antigen test?

H. pylori Stool Antigen Test: Diagnostic Approach and Treatment Strategy

Diagnostic Performance and Test Selection

Use a validated laboratory-based monoclonal antibody stool antigen test (SAT) for both initial diagnosis and post-treatment confirmation of H. pylori infection—it has equivalent accuracy to the urea breath test (UBT) with 93% sensitivity and specificity. 1

Key Testing Principles

• Laboratory-based monoclonal SAT is the recommended format with ELISA methodology, achieving high accuracy for both initial diagnosis and post-treatment testing 1
• Rapid in-office immunochromatographic stool tests have significantly limited accuracy (80-81%) and should be avoided 1, 2
• The stool antigen test detects active infection only, unlike serology which cannot distinguish current from past infection 1, 2

Medication Washout Requirements

Critical timing to avoid false-negative results:

• Stop proton pump inhibitors (PPIs) for at least 2 weeks before testing 2, 3
• Stop antibiotics and bismuth for at least 4 weeks before testing 2
• Histamine-2 receptor antagonists do not affect bacterial load and can substitute for PPIs when acid suppression is needed 2

Clinical Algorithm for H. pylori Testing

Initial Diagnosis Strategy

For patients under 50-55 years without alarm symptoms:

• Use the "test and treat" strategy with non-invasive testing (SAT or UBT) without requiring endoscopy 1, 2
• This approach reduces unnecessary endoscopies by 62% while maintaining equivalent safety and symptom resolution 1, 2

For patients over 50 years or with alarm symptoms (bleeding, weight loss, dysphagia, anemia, palpable mass):

• Proceed directly to endoscopy with invasive testing (rapid urease test, histology, or culture) 1, 2

When to Use Alternative Tests

Serology (validated IgG ELISA only) is appropriate when:

• Recent antibiotic, bismuth, or PPI use prevents adequate washout period 1, 2
• Gastric atrophy, gastric malignancies, or ulcer bleeding present (conditions causing low bacterial load) 1, 2
• However, serology has only 78% average accuracy and cannot confirm eradication 1, 2

Post-Treatment Confirmation

Perform test-of-cure at least 4 weeks after completing eradication therapy using:

• Laboratory-based monoclonal SAT (sensitivity 91.6%, specificity 98.4%) 2, 3
• Or UBT as equally acceptable alternative 1, 3
• Never use serology for post-treatment confirmation as antibodies remain elevated after eradication 1, 2

Mandatory Test-of-Cure Situations

• Complicated peptic ulcer disease 2
• Gastric ulcer 2
• Low-grade gastric MALT lymphoma 2
• Patients at high risk for gastric cancer 2

Treatment Approach

For treatment-naive patients with confirmed H. pylori:

• First-line: 14-day bismuth quadruple therapy or 14-day concomitant (non-bismuth quadruple) therapy 3, 4, 5
• In areas with low clarithromycin resistance (<15%): 14-day triple therapy is acceptable 4

For treatment failure:

• Second-line: 14-day levofloxacin triple therapy or 14-day bismuth quadruple therapy (if not previously used) 4, 5
• Multiple failures: Obtain antimicrobial susceptibility testing when available 4, 5

Common Pitfalls to Avoid

• Do not use rapid in-office stool tests—they lack adequate accuracy 1, 2
• Do not test patients currently taking PPIs—wait 2 weeks after discontinuation 2, 3
• Do not use IgA or IgM antibody tests—they have low specificity and sensitivity and are not FDA-approved 1
• Do not use serology panels (IgG/IgA/IgM combinations)—they provide no added benefit and often include unreliable tests 1, 2
• Do not skip test-of-cure in high-risk patients—eradication failure rates exceed 20% even with recommended regimens 6

Special Populations

Safe for all populations:

• Stool antigen testing is safe in children and pregnant women (unlike radioactive 14C-UBT) 2
• 13C-UBT is also safe in these populations 2

High-risk groups requiring testing:

• First-generation immigrants from high-prevalence countries 1
• Family members of patients with gastric cancer or peptic ulcer disease 1
• Patients with unexplained iron-deficiency anemia, idiopathic thrombocytopenic purpura, or vitamin B12 deficiency 1