Surveillance in Ulcerative Colitis: Narrow Band Image Versus Chromoendoscopy for High-risk Groups

Inclusion Criteria: * At least one of the followings should be satisfied; 1. A patient having extensive ulcerative colitis with 8-year or longer disease duration 2. A patient having both ulcerative colitis and primary sclerosing colitis 3. A patient having a previous history of dysplasia at the colitic segment within recent 5 years Exclusion Criteria: * All of the following conditions should be excluded for 1st surveillance colonoscopy study 1. A patient who underwent total or segment colectomy. 2. A patient who taking (warfarin or direct oral anticoagulants and cannot stop them for procedures owing to the high thromboembolic risk 3. A patient who has known thrombocytopenia (less than 80,000/µL in recent 6 months 4. A patient who has a coagulopathy 5. A patient who has chronic renal disease evidenced by serum creatinine \> 1.2 mg/dL within 6 months of study participation 6. A patient who has already undergone surveillance colonoscopy within 1 year * All of the following conditions should be excluded for 2nd surveillance colonoscopy study even if they were included in 1st surveillance study. 1. A patient who underwent total or segment colectomy after 1st surveillance colonoscopy for this trial. 2. A patient who taking (warfarin or direct oral anticoagulants and cannot stop them for procedures owing to the high thromboembolic risk 3. A patient who has known thrombocytopenia (less than 80,000/µL in recent 6 months 4. A patient who has a coagulopathy 5. A patient who has chronic renal disease evidenced by serum creatinine \> 1.2 mg/dL within 6 months of study participation