Monoclonal stool antigen test for diagnosing Helicobacter pylori in chronic atrophic gastritis: a prospective primary care study

Background/aims: ) infection in patients with chronic atrophic gastritis (CAG) remains challenging. The monoclonal stool antigen test (SAT) offers a non-invasive alternative to endoscopic methods. This study aimed to evaluate the diagnostic accuracy of SAT in CAG and to analyze its performance in relation to the severity of gastric atrophy. Methods: In this prospective study, 287 patients with CAG underwent SAT, urea breath test, serology, and histology. Patients were stratified into low-risk and high-risk groups based on gastric cancer progression risk. SAT was assessed against a reference standard combining histology and UBT. Results: The area under the ROC curve for SAT was 0.858. SAT showed a sensitivity of 75.9% and a specificity of 96.1%. In high-risk patients, SAT demonstrated comparable specificity (96.77% vs. 95.77%) and positive predictive value (95.24% vs. 93.48%) to those in low-risk patients, with numerically higher accuracy (89.29% vs. 86.05%). Consistency analysis revealed substantial agreement between SAT and the reference standard overall (κ=0.72), with stronger agreement in the high-risk patients (κ=0.77) than in the low-risk patients (κ=0.69). Conclusions: in CAG, exhibiting high specificity and strong diagnostic consistency. Its performance is positively correlated with the severity of gastric atrophy, supporting its preferential use in high-risk, advanced atrophy populations.