What type of immunoglobulin (Ig) does the Helicobacter pylori (H. pylori) blood test typically measure, IgG or IgM?

H. pylori Blood Test Uses IgG, Not IgM

The H. pylori blood test primarily measures IgG antibodies, not IgM, as IgG is the appropriate immunoglobulin for detecting chronic H. pylori infection. 1, 2

Rationale for IgG Testing

• H. pylori infection is a chronic infection, making IgG detection the appropriate immunoglobulin class to measure 1
• IgG antibodies remain elevated for months or even years after H. pylori infection, making them reliable markers for both current and past infection 1
• The preferred method for serological testing is ELISA (enzyme-linked immunosorbent assay) that specifically detects IgG antibodies 1

Limitations of IgM Testing

• IgM antibodies have very limited utility in H. pylori diagnosis
• Only about 4% of patients with H. pylori infection show elevated IgM titers 3
• Those few patients with raised IgM titers also typically have high IgG titers, making IgM testing redundant 3
• IgM is not recommended in any major guideline for H. pylori diagnosis

Performance of IgG Serology

• Validated IgG serology tests have accuracy rates exceeding 90% when properly validated 1
• IgG tests show high sensitivity (98%) for detecting H. pylori infection 4
• Commercial tests use different antigen extracts, with those containing high and low molecular weight antigens being more specific 1

Important Clinical Considerations

• Serology is the only test not affected by conditions that reduce bacterial load:

  • Recent use of antibiotics
  • Proton pump inhibitor (PPI) therapy
  • Gastric bleeding
  • Atrophic gastritis
  • Gastric malignancies 1, 2

• After successful H. pylori eradication:

  • IgG antibodies persist for months to years
  • IgG levels typically decrease by approximately 50% within 6-12 months 3, 5
  • 65% of patients remain seropositive for more than a year after successful eradication 5

Pitfalls to Avoid

• Do not use serology to confirm recent eradication (within 6 months) as antibodies remain elevated 2
• Only use validated commercial IgG tests due to variability in accuracy between different tests 1
• Rapid in-office serological tests have shown disappointing sensitivity and specificity (63-97% and 68-92%, respectively) and are not recommended 1

For optimal diagnostic accuracy, the Maastricht IV/Florence Consensus Report recommends laboratory-based ELISA tests for IgG antibodies when serological testing for H. pylori is indicated 1.