What blood test is used to diagnose Helicobacter (H.) Pylori infection?

Blood Tests for H. Pylori Diagnosis

The validated IgG serology test is the recommended blood test for diagnosing H. pylori infection, especially when patients have recently used antimicrobial or antisecretory drugs, have ulcer bleeding, atrophy, or gastric malignancies. 1

Non-Invasive Diagnostic Options for H. Pylori

H. pylori infection can be diagnosed using both invasive techniques requiring endoscopy and non-invasive methods. For blood-based testing specifically:

Serological Testing (Blood Test)

• Test type: ELISA (Enzyme-Linked Immunosorbent Assay) for IgG antibodies
• Accuracy: Varies significantly between commercial tests; only validated tests with >90% accuracy should be used 1
• Specimen: Serum sample

When to Use Serology Testing

Serology is particularly valuable in specific clinical scenarios:

1. Recent use of antibiotics (within 4 weeks)
2. Recent use of proton pump inhibitors (PPIs) (within 2 weeks)
3. Patients with bleeding ulcers
4. Patients with atrophic gastritis
5. Patients with gastric malignancies

Important Considerations for Serological Testing

• Not all serological tests are equivalent in accuracy 1
• Antibodies against H. pylori remain elevated for months or even years after the infection has cleared 1
• Cannot distinguish between current and past infection
• Does not confirm eradication after treatment (antibody titers take up to 6 months to decrease by 50%) 2

Other Non-Invasive Tests for H. Pylori

While not blood tests, these non-invasive alternatives are often preferred over serology:

1. 13C-Urea Breath Test (UBT):

   • Considered the gold standard non-invasive test 2
   • Sensitivity: 95%, Specificity: 95% 1
   • Requires stopping PPIs for 2 weeks before testing 1
   • Recommended for confirmation of eradication 2

2. Stool Antigen Test (SAT):

   • Laboratory-based monoclonal antibody tests have high accuracy 1
   • Sensitivity: 88-90%, Specificity: 91-100% 3, 4
   • Rapid in-office stool tests have limited accuracy 1
   • Requires stopping PPIs for 2 weeks before testing 1

Diagnostic Algorithm for H. Pylori Testing

1. First-line testing (in patients not on PPIs or antibiotics):

   • 13C-Urea Breath Test (preferred)
   • Laboratory-based stool antigen test using monoclonal antibodies

2. When to use serology (blood test):

   • Patient has taken PPIs within 2 weeks
   • Patient has taken antibiotics within 4 weeks
   • Patient has active bleeding ulcer
   • Patient has atrophic gastritis or gastric malignancy
   • When other tests might give false-negative results

Common Pitfalls in H. Pylori Testing

• PPI use: Can cause false-negative results in breath tests and stool tests; stop PPIs for 2 weeks before testing 1
• Antibiotic use: Can suppress bacterial load leading to false-negative results in all tests except serology 1
• Bleeding: Reduces sensitivity of rapid urease tests and other direct detection methods 5, 6
• Atrophic gastritis: May have patchy distribution of bacteria leading to sampling errors in invasive tests 1

Conclusion

While the 13C-Urea Breath Test is generally considered the gold standard non-invasive test for H. pylori diagnosis, validated IgG serology is the preferred blood test and has specific advantages in certain clinical scenarios, particularly when patients have recently used medications that might affect other test results or have conditions like bleeding ulcers or atrophic gastritis.