Supplementary Material for: Weekend effect on clinical outcomes of acute lower gastrointestinal bleeding: A large multicenter cohort study in Japan

Introduction Weekend admissions showed increased mortality in several medical conditions. This study aimed to examine the weekend effect on acute lower gastrointestinal bleeding (ALGIB) and its mortality and other outcomes. Methods This retrospective cohort study (CODE BLUE-J Study) was conducted at 49 Japanese hospitals between January 2010 and December 2019. In total, 8120 outpatients with acute hematochezia were enrolled and divided into weekend admissions and weekday admissions groups. Multiple imputation (MI) was used to handle missing values, followed by propensity score matching (PSM) to compare outcomes. The primary outcome was mortality; the secondary outcomes were rebleeding, length of stay (LOS), blood transfusion, thromboembolism, endoscopic treatment, the need for interventional radiology, and the need for surgery. Colonoscopy and computed tomography (CT) management was also evaluated. Results Before PSM, there was no significant difference in mortality (1.3% vs. 0.9%, P=0.133) between weekend and weekday admissions. After PSM with MI, 1,976 cases were matched for each admission. Mortality was not significantly different for weekend admissions compared with weekday admissions (odds ratio [OR] 1.437, 95% confidence interval [CI] 0.785-2.630; P=0.340). No significant difference was found with other secondary outcomes in weekend admissions except for blood transfusion (OR 1.239, 95% CI 1.084-1.417; P=0.006). Weekend admission had a negative effect on early colonoscopy (OR 0.536, 95% CI 0.471-0.609; P<0.001). Meanwhile, urgent CT remained significantly higher in weekend admissions (OR 1.466, 95% CI 1.295-1.660; P<0.001). Discussion/Conclusion Weekend admissions decreases early colonoscopy and increases urgent CT, but do not affect mortality or other outcomes except transfusion.