What blood test can diagnose Helicobacter (H.) Pylori infection?

Blood Tests for Diagnosing H. Pylori Infection

Serology testing (IgG antibody detection) is the primary blood test available for diagnosing H. pylori infection, but it should only be used in specific clinical scenarios due to its limitations in distinguishing between active and past infection. 1

Types of Blood Tests for H. Pylori

Serology (IgG) Testing

• Detects IgG antibodies against H. pylori in serum samples
• Sensitivity: approximately 85%
• Specificity: approximately 79% 1
• Not all serological tests are equivalent - only validated IgG serology tests should be used due to variability in accuracy between commercial tests 2

13C-Urea Blood Test

• A newer alternative method that measures 13C in blood rather than breath
• Shows high sensitivity (92-98%) and specificity (96-100%) compared to urea breath test and rapid urease test 3
• Not yet widely adopted in clinical practice

When to Use Serology Testing

Serology is appropriate in specific clinical scenarios:

• When patients cannot stop proton pump inhibitors (PPIs) for the required 2 weeks before testing 2, 1
• In the setting of recent antimicrobial drug use 2
• In cases of ulcer bleeding 2
• In patients with gastric atrophy or gastric malignancies where bacterial load may be permanently low 2
• For initial screening in high-prevalence populations 1

Limitations of Serology Testing

• Cannot distinguish between active and past infection 1
• Not recommended for confirming eradication after treatment 1
• Accuracy varies significantly between commercial tests 2
• Lower specificity compared to other non-invasive tests 1

Preferred Non-Invasive Diagnostic Tests

While blood tests are available, the preferred non-invasive tests for H. pylori diagnosis are:

1. Urea Breath Test (UBT)

   • Gold standard non-invasive test with sensitivity of 94.7% and specificity of 95.7% 1
   • Requires stopping PPIs for 2 weeks before testing 2, 1

2. Stool Antigen Test (SAT)

   • Excellent alternative to UBT with sensitivity of 94-95% and specificity of 97-100% 1
   • Laboratory-based monoclonal tests have equivalent accuracy to UBT 2
   • Rapid in-office stool tests have limited accuracy 2

Important Considerations for Testing

• PPIs should be stopped for 2 weeks before testing by culture, histology, rapid urease test, UBT, or stool test 2
• For post-treatment confirmation, UBT or stool antigen test should be used at least 4-8 weeks after completing therapy 1
• Whole blood rapid tests (like FlexSure HP) have lower sensitivity (84%) compared to laboratory serum tests 4

Common Pitfalls to Avoid

• Using serology to confirm eradication after treatment 1
• Testing too soon after treatment completion 1
• Failing to stop PPIs before testing 1
• Using non-validated serological tests 2
• Relying on rapid in-office stool tests instead of laboratory-based monoclonal tests 2

When diagnosing H. pylori infection, consider the clinical context, availability of tests, and recent medication use to select the most appropriate diagnostic approach.