Is the blood test for Helicobacter pylori (H. pylori) accurate?

Blood Test Accuracy for H. pylori

Blood tests (serology) for H. pylori are not sufficiently accurate for clinical use, with sensitivity of only 85% and specificity of 79%, and should not be used when better alternatives are available. 1

Why Blood Tests Are Inadequate

Limited Diagnostic Accuracy

• Laboratory-based ELISA serology tests demonstrate an overall accuracy averaging only 78% (range 68-82%) 1
• The accuracy of serological tests is no longer adequate to justify their use on clinical or economic grounds 1
• Near-patient (fingerprick) blood tests perform even worse, with mean sensitivity of only 71.1% and specificity of 87.6% 1

Critical Limitation: Cannot Distinguish Active from Past Infection

• Serology detects antibodies that indicate exposure to H. pylori at some time, but cannot differentiate between current active infection and previously eradicated infection 1, 2
• Antibody levels persist in blood for months to years after successful eradication 1, 2
• As more patients receive treatment for H. pylori, the proportion with persistent antibodies increases, leading to more false-positive results 1

Inappropriate for Post-Treatment Confirmation

• Serology tests should never be used to confirm cure after H. pylori treatment 1, 3
• The American College of Gastroenterology states there is no role for serology in determining eradication success 3

When Blood Tests May Be Acceptable

Limited Clinical Scenarios

Blood tests have only one appropriate use:

• Validated IgG serology may be used in settings where other tests are unreliable: recent antimicrobial or antisecretory drug use, active ulcer bleeding, gastric atrophy, or gastric malignancies 1
• This is because serology is the only test unaffected by local gastric changes that reduce bacterial load and cause false-negative results with other methods 1

Superior Alternatives to Blood Tests

For Initial Diagnosis

• Urea breath test (UBT): sensitivity 94.7-97%, specificity 95-95.7% 1, 3
• Stool antigen test (monoclonal, laboratory-based): sensitivity 93.2%, specificity 93.2% 2, 3
• Both tests detect active infection, not just past exposure 2

For Post-Treatment Confirmation

• Stool antigen test is superior to blood tests for follow-up because it detects current H. pylori presence, not just antibodies 2
• Testing must be performed at least 4 weeks after completing treatment 4, 3
• Proton pump inhibitors should be discontinued for at least 7 days (preferably 2 weeks) before testing 4, 3
• Antibiotics and bismuth should be withheld for at least 4 weeks before testing 1, 4

Common Pitfalls to Avoid

Technical Issues with Fingerprick Tests

• Fingerprick blood test results vary when obtaining blood is difficult 1
• Squeezing the finger changes hematocrit by mixing tissue fluid with blood, altering antibody concentration 1
• Whole blood tests are affected by chylomicrons, which interfere with membrane permeability in diagnostic tests 1

Clinical Decision-Making Errors

• Do not use blood tests when stool antigen or breath tests are available 2
• Never use blood tests to confirm eradication after treatment 1, 3
• Only use validated laboratory-based ELISA tests if serology is necessary; avoid office-based rapid tests 1