H. pylori Stool Antigen Test Specificity
The H. pylori stool antigen test has a specificity of greater than 90% in untreated patients, with the monoclonal antibody version achieving approximately 93-97% specificity. 1
Test Performance Characteristics
Pre-Treatment Diagnostic Accuracy
The polyclonal stool antigen test demonstrates a specificity of 93.2% in untreated patients based on weighted analysis of 3,419 patients evaluated before therapy 1
The monoclonal stool antigen test achieves superior specificity of approximately 97% compared to polyclonal versions, with clearer distinction between positive and negative results 2, 3
Multiple consensus guidelines from the American College of Cardiology Foundation and American College of Gastroenterology report specificity exceeding 90% for the stool antigen test in initial diagnosis 1
Post-Treatment Confirmation
Specificity drops to 87.6% when using the polyclonal test for confirmation of eradication 4-8 weeks after treatment 1
The monoclonal stool antigen test maintains excellent specificity post-treatment, though the exact percentage varies by study 3
Post-treatment accuracy is affected by timing, with testing recommended no earlier than 4 weeks after completion of therapy 2
Important Clinical Caveats
Factors That Reduce Specificity
Proton pump inhibitors must be discontinued for at least 2 weeks before testing to avoid false results, as they can affect test accuracy 2
Antibiotics and bismuth should be withheld for at least 4 weeks prior to stool antigen testing 1, 2
Patients with gastrointestinal bleeding may have suboptimal specificity, making the test less reliable in this population 3
Test Selection Matters
Laboratory-based monoclonal antibody tests are significantly more accurate than polyclonal versions, with specificity approaching 97% versus 93% 2, 3
The test requires laboratory processing by trained personnel and cannot be performed as a point-of-care test 1
Comparison to Other Diagnostic Methods
The urea breath test achieves slightly higher specificity of 95-97.7% compared to stool antigen testing 1, 2, 4
Serologic antibody tests have lower specificity of approximately 90% and cannot distinguish active from past infection 1
Rapid urease testing from endoscopic biopsies demonstrates specificity of 95-100% but requires invasive procedures 1
The stool antigen test performs comparably to the urea breath test for initial diagnosis and can be used interchangeably in clinical practice, though the monoclonal version should be preferentially selected when available. 1, 2