Safety of Cold Snare Polypectomy in Patients With Uninterrupted Antiplatelet Agent

* Cold snare polypectomy (CSP): resection of colorectal polyp by mechanical force of snare, without electric cautery. * Antiplatelet agent: single use of aspirin or clopidogrel * Uninterrupted (continuous) use of antiplatelet agent: cessation of antiplatelet agent less than 4 days. Cessation of antiplatelet agent is sum of before and after the CSP ex.) 1. patient who stopped aspirin only on the day of colonoscopy and resumed the day after colonoscopy -\> cessation of aspirin was 1 day. 2. patient who stopped aspirin only on the day of colonoscopy and resumed the 2 days after colonoscopy -\> cessation of aspirin was 2 days (before colonoscopy 1day + after colonoscopy 1day). 3. patient who stopped aspirin from 3 days before colonoscopy and resumed the day after colonoscopy -\> cessation of aspirin was 4 days (-3, -2, -1, 0=on the day of colonoscopy). -\> interruption of aspirin -\> excluded from study. 4. patient who stopped aspirin from 2 days before colonoscopy and resumed 2 days after colonoscopy -\> cessation of aspirin was 4 days (-2, -1, 0=on the day of colonoscopy, 1=the day after colonoscopy). -\> interruption of aspirin -\> excluded from study. * BLEEDING # Immediate (intraprocedural) bleeding After CSP, bleeding will be observed for 2 minutes. Bleeding grade: (1) no bleeding, (2) minor (negligible) bleeding, (3) major bleeding, and (4) active bleeding (spurting). In case of Grade 3 or 4, hemoclipping will be applied * Delayed bleeding Delayed bleeding will be defined when all of the following criteria were met: (1) anal bleeding after discharge of endoscopy unit and (2) identification of polypectomy bleeding site by colonoscopy. * Significant delayed bleeding Any of the following criteria: (1) hemoglobin drop \>2, (2) hemodynamic instability, (3) admission, (4) transfusion, and (5) surgery or angiography for hemostasis.