How long after H. Pylori (Helicobacter Pylori) infection does the serum antigen test remain positive?

Duration of Serum Antibody Positivity After H. Pylori Infection

Serum antibodies against H. pylori remain elevated for months to years after the disappearance of H. pylori from the stomach, making serology tests unsuitable for confirming eradication. 1

Understanding H. pylori Diagnostic Tests and Their Persistence

H. pylori diagnostic tests can be categorized into two main groups:

Tests for Active Infection

1. Urea Breath Test (UBT)

   • Gold standard for non-invasive diagnosis
   • Sensitivity and specificity >90% 1
   • Detects current, active infection
   • Becomes negative within 4-8 weeks after successful eradication

2. Stool Antigen Test (SAT)

   • Laboratory-based monoclonal antibody tests have high accuracy (sensitivity and specificity >90%) 1
   • Detects current, active infection
   • Becomes negative shortly after successful eradication
   • Rapid in-office stool tests have limited accuracy and are not recommended 1

Antibody-Based Tests

1. Serum Antibody Tests
   • Detect IgG antibodies against H. pylori
   • Key limitation: Cannot distinguish between current and past infection 1
   • Antibodies persist for "months, even years" after H. pylori eradication 1
   • Should only be used for initial diagnosis, not for confirming cure 1

Clinical Implications

• For initial diagnosis: Both UBT, SAT, and validated serology tests can be used
• For post-treatment confirmation: Only UBT or SAT should be used, never serology 1
• Special situations: Serology is the only reliable test when:
  • Patient is on PPI therapy (should be stopped 2 weeks before other tests)
  • Recent antibiotic use (within 4 weeks)
  • Bleeding ulcers
  • Extensive gastric atrophy or intestinal metaplasia 1

Important Considerations

• The accuracy of serological tests varies considerably between commercial kits; only validated tests with >90% accuracy should be used 1
• In populations with low H. pylori prevalence, the positive predictive value of serology tests decreases significantly 1
• Office-based serologic tests are less accurate than laboratory-based ELISA tests 1
• Serology tests may remain positive in up to 30% of patients even 4 years after successful eradication 1

Testing Algorithm

1. Initial diagnosis: UBT, SAT, or validated serology
2. Confirmation of eradication: Wait at least 4 weeks after treatment completion, then use UBT or SAT only
3. If patient is on PPIs: Either stop PPI for 2 weeks before testing with UBT/SAT or use validated serology (understanding its limitations) 1

Pitfalls to Avoid

• Never use serology to confirm H. pylori eradication
• Do not perform UBT or SAT within 2 weeks of PPI use or 4 weeks of antibiotic therapy
• Be aware that in areas with high prevalence of gastric atrophy (e.g., East Asia), stool antigen tests may have lower sensitivity compared to serology 2

In summary, while UBT and SAT become negative within weeks after successful H. pylori eradication, serum antibodies can persist for months to years, making serology unsuitable for post-treatment evaluation.