Do You Need to Stop PPIs Before a Stool Antigen Test for H. pylori?
Yes, you must stop PPIs for at least 2 weeks before performing a stool antigen test for H. pylori to avoid false-negative results. 1
Why PPIs Must Be Stopped
PPIs increase gastric pH, which decreases the H. pylori bacterial load in the stomach, particularly in the antrum. This reduction causes false-negative results in 10-40% of cases. 1 The mechanism is straightforward: by suppressing acid, PPIs create an environment where H. pylori organisms temporarily decrease in number or shift their distribution proximally in the stomach, making them harder to detect. 2
Specific Washout Periods
The evidence provides clear guidance on medication cessation:
- PPIs: Stop for 2 weeks (some sources suggest a minimum of 7 days may be sufficient, but 2 weeks is the standard recommendation) 1
- Antibiotics and bismuth: Stop for at least 4 weeks 1
- Fasting: At least 6 hours before stool collection 1
The 2-week washout allows H. pylori bacteria to repopulate the stomach, restoring test sensitivity. 1 However, note that no studies have definitively evaluated the optimal washout period after long-term PPI treatment, so longer durations may be prudent in patients on chronic PPI therapy. 1
What If You Cannot Stop PPIs?
If stopping PPIs is not clinically feasible (e.g., severe GERD symptoms, recent bleeding), you have two options:
Use validated IgG serology instead - This is the only test unaffected by PPI use because antibodies remain elevated despite transient decreases in bacterial load. 1 However, serology only indicates exposure to H. pylori at some point, not active infection, and should only be used for initial diagnosis, never for confirming eradication. 1
Substitute H2-receptor antagonists - These can be used for acid suppression during the washout period without significantly affecting bacterial load or test accuracy. 1
Critical Interpretation Point
A positive stool antigen test result can be trusted even if the patient is on PPIs, because PPIs cause false-negative results but not false-positive results. 1 Only negative results during PPI therapy should raise concern about accuracy and prompt either repeat testing after appropriate washout or alternative testing with serology. 1
Common Pitfalls to Avoid
- Failing to ask about over-the-counter PPI use - Many patients take PPIs without prescription, and this must be explicitly queried. 3
- Testing too soon after stopping PPIs - The bacteria need time to repopulate; inadequate washout leads to persistent false-negatives. 1
- Using the stool antigen test in patients with active GI bleeding - Test accuracy is significantly compromised in this setting (sensitivity 82%, specificity 68% vs. 93%/93% in non-bleeding patients), so alternative diagnostic approaches should be considered. 4
Test Performance When Done Correctly
When PPIs are appropriately discontinued, the stool antigen test demonstrates excellent accuracy with >90% sensitivity and specificity in untreated patients. 1, 5 The monoclonal stool antigen tests perform even better (96% sensitivity, 97% specificity) compared to polyclonal versions. 5