What is the recommended approach for H. Pylori (Helicobacter Pylori) antigen testing using blood work?

H. Pylori Antigen Testing Recommendations

Blood-based serology testing is the recommended approach for H. pylori detection when acid-suppressing medications cannot be stopped, but it only detects antibodies and cannot distinguish between active infection and past exposure. 1

Diagnostic Options for H. pylori

The most reliable non-invasive tests for H. pylori detection include:

1. Urea Breath Test (UBT):

   • Sensitivity: 88-95%, Specificity: 95-100% 1
   • Requires stopping PPIs for at least 2 weeks before testing
   • Gold standard for non-invasive diagnosis

2. Stool Antigen Test (SAT):

   • Sensitivity: 94%, Specificity: 92% 1
   • Laboratory-based monoclonal tests are preferred over rapid in-office tests 2
   • ELISA format with monoclonal antibody is recommended 2

3. Serology (Blood) Testing:

   • Only validated IgG serology tests should be used due to variability in accuracy 2
   • Cannot distinguish between active infection and past exposure 1
   • Remains positive for months or years after eradication 1

When to Use Serology (Blood) Testing

Blood-based serology testing is particularly valuable in specific situations:

• When patients are currently using antimicrobial or antisecretory drugs 2
• In cases of ulcer bleeding 2
• In patients with atrophy and gastric malignancies 2
• When the gastric bacterial load may be low due to medication use 2

Testing Protocol Considerations

• For UBT: Patient should fast for at least 6 hours and stop PPIs for 2 weeks 1
• For SAT: Requires proper laboratory processing and an acorn-sized stool sample 1
• For Serology: No special preparation needed, making it convenient when medications cannot be stopped 1

Patient Selection Based on Age and Symptoms

• Patients under 45 years without alarm symptoms can be tested for H. pylori in primary care settings 2
• Patients over 45 years with severe dyspeptic symptoms or any patients with alarm symptoms (anemia, weight loss, dysphagia) should be referred to a specialist for endoscopy 2

Common Pitfalls to Avoid

1. False negatives with breath or stool tests:

   • PPIs can cause 10-40% false-negative rate in breath tests 1
   • H2-receptor antagonists also impact results but to a lesser extent 1

2. Serology limitations:

   • Cannot confirm eradication after treatment 1
   • Not all commercial tests are equally accurate - only validated tests should be used 2

3. Stool test accuracy:

   • Significantly reduced accuracy in patients with bleeding peptic ulcers 1
   • Rapid in-office stool tests have limited accuracy compared to laboratory tests 2

Follow-up Testing After Treatment

• Testing should be performed at least 4 weeks after completion of eradication therapy 1
• UBT or SAT are preferred for confirming eradication (not serology) 1

Blood-based serology testing for H. pylori is valuable in specific clinical scenarios, but clinicians should be aware of its limitations in distinguishing active infection from past exposure. For initial diagnosis when medications can be stopped, UBT remains the preferred non-invasive test, with laboratory-based stool antigen testing as a good alternative.