What is the next step for confirming H. pylori (Helicobacter pylori) diagnosis in a patient with abdominal symptoms, mainly pain and gastrointestinal (GI) upset, after a negative stool antigen test?

Next Steps After Negative H. pylori Stool Antigen Test in Symptomatic Patient

The urea breath test (UBT) is the recommended next step for confirming H. pylori diagnosis in a patient with abdominal pain and GI upset who has a negative stool antigen test. 1

Diagnostic Accuracy of Available Tests

• The stool antigen test has high sensitivity (93.2%) and specificity (93.2%) for initial diagnosis of H. pylori, but false negatives can occur 1, 2
• The urea breath test (UBT) is considered the gold standard non-invasive test with sensitivity and specificity >90% for active infection 1, 3
• Serological tests detect antibodies to H. pylori but cannot differentiate between current infection and previous exposure, making them unsuitable for confirmation after a negative stool test 1, 2
• The accuracy of serological tests averages only 78% (range 68-82%), significantly lower than UBT or stool antigen tests 1, 2

Important Considerations Before Testing

• Prior to UBT testing, patients should:
  • Discontinue antibiotics and bismuth for at least 4 weeks 1
  • Stop proton pump inhibitors (PPIs) for at least 7 days 1
  • Fast for at least 6 hours 1
• PPIs can cause false-negative results by decreasing the bacterial load in the stomach 1
• If PPIs cannot be stopped, validated IgG serology can be performed, though it's less accurate 1

How the Urea Breath Test Works

• Patient drinks a preparation containing labeled urea (13C or 14C) 1
• H. pylori bacteria metabolize the urea, producing labeled CO2 that is absorbed into the bloodstream 1, 4
• Labeled CO2 is exhaled and measured to determine presence or absence of H. pylori 1, 3
• 13C-UBT is preferred as it's non-radioactive and can be used in pregnant women and children 3

Alternative Diagnostic Options

• If UBT is unavailable or contraindicated, consider:
  • Repeat stool antigen testing after ensuring proper medication washout period 1, 5
  • Endoscopy with biopsy for histology, rapid urease test, and culture (especially in patients >50 years or with alarm symptoms) 1
  • Culture and susceptibility testing if clarithromycin resistance is suspected in the region 1

Clinical Algorithm

1. First, ensure patient has been off PPIs for at least 7 days and antibiotics for 4 weeks 1
2. Perform 13C-UBT as the next diagnostic step 1, 3
3. If UBT is positive, treat with appropriate eradication therapy 1
4. If UBT is negative but symptoms persist, consider other causes of abdominal pain and GI upset 1
5. For patients who cannot stop PPIs or when UBT is unavailable, consider endoscopy with biopsy 1

Pitfalls to Avoid

• Do not rely on serological tests for confirmation after a negative stool test, as they only indicate exposure, not active infection 1, 2
• Avoid testing too soon after antibiotic or PPI therapy, which can lead to false-negative results 1
• Remember that the stool antigen test and UBT have comparable accuracy when properly performed, so discordant results warrant careful evaluation 1, 5
• Do not use serological tests to confirm cure after treatment, as antibody levels often remain elevated after H. pylori elimination 1, 2