Stool antigen assay (HpSA) is less reliable than urea breath test for post-treatment diagnosis of Helicobacter pylori infection C. BILARDI*, R. BIAGINI*, P. DULBECCO*, E. IIRITANO*, C. GAMBARO*, M. R. MELE*, P. BORRO*, L. TESSIERI*, P. ZENTILIN*, C. MANSI*, S. VIGNERI  & V. SAVARINO* *Dipartimento di Medicina Interna e Specialita ` Mediche, Universita ` di Genova, Genova, Italy;  Dipartimento di Medicina Clinica e Patologie Emergenti, Universita ` di Palermo, Palermo, Italy Accepted for publication 3 July 2002 SUMMARY Background: The diagnostic yield of the stool antigen test (HpSA) in evaluating the results of Helicobacter pylori eradication therapy is controversial, but many studies have used only the 13 C-urea breath test ( 13 C-UBT) as a gold standard which has greatly reduced their relevance. Aim: To compare the reliability of HpSA and 13 C-UBT in patients post-treatment using biopsy-based methods as reference tests. Methods: A total of 100 consecutive dyspeptic patients (42 male and 58 female; mean age, 56 ± 18 years) were enrolled in our study. All patients were H. pylori positive on the basis of at least two biopsy-based methods, and underwent 1 week of treatment with various triple therapies. They were again endoscoped 4 weeks after completing therapy and six biopsy speci- mens were taken from the gastric antrum and corpus for rapid urease test, histology and culture. HpSA and 13 C- UBT were also performed within 3 days of the second endoscopy. Results: On the basis of biopsy-based tests, infection was eradicated in 77 patients but continued in 23. Three false negatives were observed with HpSA and two with 13 C-UBT. In contrast, the number of false positives was significantly higher (P < 0.01) with HpSA than with 13 C-UBT (nine vs. one), confirming the lower specificity of the former test. The overall accuracy of HpSA was 88% vs. 97% for 13 C-UBT (P < 0.02). Conclusions: HpSA has lower diagnostic value than 13 C- UBT in the evaluation of the outcome of anti-H. pylori therapy. 13 C-UBT remains the first-line diagnostic method to monitor eradication results. The use of HpSA should be reserved for those settings in which 13 C-UBT is not available. I NTRODUCTION Helicobacter pylori is a Gram-negative bacterium which is strongly implicated in the most important gastroduode- nal diseases, such as chronic gastritis, peptic ulcer and mucosa-associated lymphoid tissue lymphoma. 1, 2 Its eradication prevents both the recurrence and complica- tions of peptic ulcer and determines the regression of chronic gastritis and low-grade mucosa-associated lym- phoid tissue lymphoma. 3–5 Various diagnostic tests have been developed for the diagnosis of this relevant infection. Some techniques are invasive (rapid urease test, histology and culture) because they require endoscopy, and others are non- invasive [serology, urea breath test (UBT) and stool antigen assay (HpSA)] because they are independent of endoscopy. The use of non-invasive tests has become popular due to the better compliance of patients. Their main indication is universally recognized to be the evaluation Correspondence to: Professor V. Savarino, Dipartimento di Medicina Interna e Specialita ` Mediche, Universita ` degli Studi di Genova, Viale Benedetto XV, n. 6, 16132 Genova, Italy. E-mail: vsavarin@unige.it Aliment Pharmacol Ther 2002; 16: 1733–1738. doi:10.1046/j.0269-2813.2002.01345.x Ó 2002 Blackwell Science Ltd 1733