Background: Some case series and cohort studies suggest that acute GI bleeding decreases the sensitivity of Helicobacter pylori diagnostic testing. Objective: To assess H pylori biopsy testing in patients with acute upper-GI bleeding and 1 month later. Design: Prospective cohort study using patients as their own controls. Setting: Urban county hospital. Patients: Sixty-one patients with acute variceal bleeding. Interventions: Antral and body endoscopic biopsies at admission and 1 month later. Main outcome measurements: CLO test and histologic examinations were performed and bi opsy specimens were coded and mixed for blinded histologic examination for H pyl ori density and inflammation. Results: CLO test results changed from H pylori ne gative at baseline to H pylori positive at 1 month in two patients (3%), from H pylori positive to H pylori negative in 6 patients (10%), and remained the sam e in 53 (87%). Histologic results changed from H pylori negative at baseline to H pylori positive at 1 month in two patients (3%), from H pylori positive to H pylori negative in 5 patients (8%),and remained the same in 54 (89%). Changes occurred only in patients with low H pylori density. No significant increase in H pylori density or change in inflammatory cell infiltration was seen. CLO test sensitivity was 8%higher with bleeding vs. 1 month after bleeding (79%vs. 71% ; 95%CI of difference was 11%to 27%; i.e., maximal potential decrease in sens itivity with bleeding is 11%). Limitations: The population is not one for which H pylori testing is recommended, and biopsy test performance was less consisten t than expected. Conclusions: Acute-GI bleeding did not decrease the sensitivit y of rapid urease testing, unless the effect lastsmore than 1 month. Furthermore , bleeding did not produce falsely negative histologic examinations for H pylori , decrease H pylori density, or alter inflammatory cell infiltration. However, g iven the lower than expected overall CLO test sensitivity and frequent use of pr oton pump inhibitors for GI bleeding, histology may be preferred in this setting . Background: Some case series and cohort studies suggest that acute GI loss decreases the sensitivity of Helicobacter pylori diagnostic testing. Objective: To assess H pylori biopsy testing in patients with acute upper-GI bleeding and 1 month later. Design: Prospective cohort study using patients Patients: Sixty-one patients with acute variceal bleeding. Interventions: Antral and body endoscopic biopsies at admission and 1 month later. Main outcome measurements: CLO test and histologic examinations were performed and bi opsy Results: CLO test results changed from H pylori ne gative at baseline to H pylori positive at 1 month in two patients (3%), from H pylori positive to H pylori negative in 6 patients (10%), and remained the sam e in 53 (87%). Histologic results changed from H pylori negative at baseline to H pylori positi ve at 1 month in two patients (3%), from H pylori positive to H pylori negative in 5 patients (8%), and remained the same in 54 (89%). Changes occurred only in patients with low H pylori density. No significant increase in H pylori density or change in inflammatory cell infiltration was seen. CLO test sensitivity was 8% higher with bleeding vs. 1 month after bleeding (79% vs. 71%; 95% CI of difference was 11% to 27% ; ie, maximal potential decrease in sensitivity with bleeding is 11%). Limitations: The population is not one for which H pylori testing is recommended, and biopsy test performance was less consisted than expected. Conclusions: Acute-GI bleeding did not decrease the sensitivit y of rapid urease testing, unless the effect lastsmore than 1 month. However, given the lower than expected overall CLO test sensitivity and frequent use of proton pump inhibitors for GI bleeding, histology may be preferred in this setting.