The accuracy of the Helicobacter pylori stool antigen test in diagnosing H. pylori in treated and untreated patients.

Objective and Design: To evaluate the performance of the Helicobacter pylori stool antigen test (HpSA test) in detecting H. pylori infection and monitoring the effect of treatment. This was done in two separate studies using either a biopsy or the 13C-urea breath test based 'gold standard' (in untreated and treated patients, respectively).
Setting: Endoscopy units of two general hospitals.
Patients: One hundred and twenty-eight dyspeptic patients undergoing endoscopy in the first study. Sixty-five patients receiving anti-H. pylori treatment in the second study.
Results: Sensitivity and specificity in untreated patients were 96.3% and 81.8%, respectively. Seven days after treatment, these figures were 20% and 95%, and 4 weeks after treatment they were 40% and 95%.
Conclusion: The HpSA test is accurate in untreated patients but fails in monitoring treatment success.