What is the role of blood tests in diagnosing H. pylori (Helicobacter pylori) infection?

Role of Blood Tests in Diagnosing Helicobacter pylori Infection

Serological blood tests are not recommended as the primary diagnostic method for H. pylori infection due to their inability to distinguish between active infection and past exposure, with stool antigen tests or urea breath tests being the preferred non-invasive diagnostic methods. 1

Limitations of Serological Testing

• Serological tests detect anti-H. pylori IgG antibodies in serum but cannot reliably differentiate between active infection and previous exposure, as antibody levels persist in blood for long periods after eradication 2
• The overall accuracy of commercial ELISA serology tests averages only 78% (range 68-82%), which is inadequate for clinical use on both clinical and economic grounds 2
• Serological tests cannot be used to confirm eradication after treatment as antibodies remain elevated after H. pylori elimination 2
• False positive results are particularly common with serology, making it unreliable for confirming active infection 2

Preferred Non-Invasive Diagnostic Tests

• The Urea Breath Test (UBT) is considered the most accurate non-invasive test with excellent sensitivity (94.7-97%) and specificity (95-95.7%) 1
• Stool Antigen Test directly detects H. pylori bacterial antigens in stool specimens with sensitivity and specificity of approximately 93%, comparable to UBT 2
• Both UBT and stool antigen tests detect active infection rather than just past exposure, making them valuable for both initial diagnosis and confirmation of eradication 2, 1

Limited Situations Where Serology May Be Useful

• Serology is the only test not affected by local changes in the stomach that could lead to a low bacterial load and false-negative results of other tests 2
• Serology may be appropriate when patients have recently used antibiotics, bismuth products, or proton pump inhibitors (PPIs), which can cause false-negative results with other testing methods 2
• In patients with gastric atrophy, gastric malignancies, or ulcer bleeding, serology may be more reliable than other non-invasive tests 2

Important Testing Considerations

• Proton pump inhibitors should be stopped for at least 2 weeks before testing by culture, histology, rapid urease test, UBT, or stool test to avoid false-negative results 2
• Histamine-2 receptor antagonists do not affect bacterial load and can be substituted for a PPI when acid suppression is needed before testing 2
• For confirmation of eradication, testing should be performed no earlier than 4 weeks after completion of treatment 1

Algorithm for H. pylori Testing

1. For initial diagnosis in primary care setting:

   • First choice: 13C-urea breath test (UBT) or laboratory-based monoclonal stool antigen test 2
   • If patient has recently used antibiotics or PPIs: Consider validated IgG serology or wait 2 weeks after stopping these medications 2

2. For patients requiring endoscopy (due to alarm symptoms, age >50 with new-onset dyspepsia, or treatment failures):

   • Perform rapid urease test, histology, or culture during endoscopy 2
   • Consider immunohistochemical staining for H. pylori when results are equivocal 2

3. For confirmation of eradication:

   • Use UBT or stool antigen test at least 4 weeks after completion of treatment 1
   • Do not use serology to confirm eradication 2, 1

Pitfalls to Avoid

• Rapid in-office serological tests have limited accuracy (sensitivity 71.1%, specificity 87.6%) and should be avoided 2
• Failure to stop PPIs before testing can lead to false-negative results in all tests except serology 2
• Relying solely on serology for diagnosis in low-prevalence populations will lead to many false positives 1
• Using panels of IgG, IgA, and IgM tests provides no added benefit over validated IgG tests and may include non-FDA-approved tests of unclear diagnostic value 2