Guidelines for Colonic Diverticular Disease—2026, Second Edition: Management of Diverticular Bleeding and Acute Diverticulitis

Colonic diverticular disease is becoming increasingly common in Japan, paralleling population aging and changes in lifestyle and medication use. The predominance of right-sided diverticulosis in Asian populations, in contrast to the left-sided predominance in Western populations, influences clinical presentation and management. In Japan, diverticulitis has become a clinically important problem, and diverticular bleeding is currently the most frequent cause of acute lower gastrointestinal bleeding (LGIB). The Japanese Gastroenterological Association updated its clinical guidelines for diverticular bleeding and diverticulitis in 2026. Key domains including epidemiology, diagnostic and therapeutic strategies, and priority clinical and future research questions were addressed. Evidence was graded using the Grading of Recommendations Assessment, Development and Evaluation approach, and recommendations were formulated via a modified Delphi process with external review. These guidelines aim to provide Japanese and Asian evidence-based consensus that complements Western guidelines. Recommendations for acute LGIB and diverticular bleeding are as follows: risk stratification with the Shock Index and Oakland and NOBLADS scores guides triage; pre-colonoscopy contrast-enhanced computed tomography is the widely used diagnostic modality; routine colonoscopy within 24 h is not suggested for all patients; endoscopic band ligation or direct clipping is suggested post-detection of stigmata of recent hemorrhage; and early oral refeeding is suggested. Recommendations for diverticulitis are as follows: post-resolution colonoscopy is suggested to exclude colorectal cancer; outpatient treatment and withholding of antibiotics are suggested in selected uncomplicated cases; and primary anastomosis may be favored over Hartmann's procedure in selected complicated cases.