Validation of a monoclonal stool antigen test for diagnosing Helicobacter pylori infection in young children.

BACKGROUND AND OBJECTIVE: The monoclonal stool antigen test for diagnosing Helicobacter pylori infection in children has been tested in developed countries, showing sensitivity and specificity higher than 90%. However, its accuracy in young children from developing countries is not well established. The aim of the study was to determine the accuracy of the monoclonal stool antigen test for diagnosing H pylori infection in children up to 7 years old. PATIENTS AND METHODS: Two hundred seventy-six patients (53.6% female; ages 0.35-6.99 years) were evaluated. Gold standard positive culture or positive histology and rapid urease tests were performed. The test (Amplified IDEIATM Hp StAR) was done according to the manufacturer's instructions. Results were expressed as optical density (OD) and an OD more than or equal to 0.190 was considered positive. Additionally, a receiver operating characteristic curve was used to find the best cutoff. RESULTS: The monoclonal stool antigen test for diagnosing H pylori infection showed 100% sensitivity (95% confidence interval [CI] 92.7%-100%) and 76.2% specificity (95% CI 70.1%-81.4%), considering the manufacturer's cutoff. After setting a new cutoff with the receiver operating characteristic curve (OD = 0.400), sensitivity remained 100% (95% CI 92.7%-100%), but the specificity improved to 97.7% (95% CI 94.7%-99%). At ages up to 2 years, sensitivity was 100% (95% CI 43.8%-100%) and specificity was 100% (95% CI 92.4%-100%); at ages 2 to 4 years, 100% (95% CI 80.6%-100%) and 97.6% (95% CI 96%-99.2%); at ages older than 4 years, 100% (95% CI 88.6%-100%) and 96.6% (95% CI 94.7%-98%), respectively. CONCLUSIONS: The monoclonal stool antigen test is accurate for diagnosing H pylori in children younger than 7 years old, but it must be locally validated in order to find the best cutoff for each population.