Lack of accuracy of the noninvasive stool antigen test in patients with gastroduodenal ulcer bleeding

OBJECTIVE: The antigen-based stool assay has proven to be accurate in diagnosing Helicobacter pylori infection in dyspeptic patients. We evaluated the H. pylori antigen-based stool assay (HpSA) in patients with peptic ulcer bleeding (PUB). METHODS: Thirty-six patients with PUB were endoscoped, and antral and corpus biopsy specimens were taken for rapid urease test (RUT), histology, and culture. The first stool sample after admission was collected for the HpSA test. The gold standard was defined as either positive culture or positive RUT and histology. If only RUT or histology was positive, this was defined as indeterminate. To evaluate cross-reaction with blood constituents, citrated blood samples from 10 healthy volunteers (nine H. pylori serology negative and one H. pylori serology positive) were assessed by the HpSA test. RESULTS: A total of 36 consecutive patients with PUB (21 male) with a mean age of 69.5 yr were included in the study. Using the gold standard, the sensitivity and specificity of the HpSA test were 100% and 52%, respectively. Citrated blood samples of three H. pylori negative and one H. pylori positive volunteer gave a positive result in the HpSA test, suggesting cross-reaction with blood constituents. CONCLUSIONS: The HpSA test gave a high number of false-positive results in patients with PUB, probably because of blood constituents cross-reacting in the enzyme immunoassay. The HpSA test is not accurate for testing H. pylori infection in patients with PUB.