Small colon polyps which are found during colonoscopy insertion are sometimes difficult to find during withdrawal and thus missed. The investigators aim to evaluate the differences of colon polyp/adenoma detection rates of patients undergoing additional inspection and polypectomy during insertion as compared to the patients undergoing traditional practice of careful inspection and polypectomy performed entirely during withdrawal of colonoscopy.

Participants will be randomly assigned by a research assistant, by using a computer-generated randomization sequence to undergo colonoscopy with either inspection and polypectomy during both insertion and withdrawal of colonoscope (study group) or inspection and polypecotmy entirely during withdrawal of colonoscope (control group). Randomization will be done via concealed allocation with a sealed envelope that designate study group or control group.

Colonoscopies will be performed by two experienced investigators by using a standard colonoscopy (CF-Q260AI or CF-Q260AL; Olympus Medical Systems Corp., Tokyo, Japan). All procedures are performed under moderate conscious sedation with fentanyl (United Biomedical, Taipei, Taiwan) and midazolam (Dormicum; Roche Pharmaceuticals, Basel, Switzerland) according to the current guidelines. Carbon dioxide insufflation is used for all endoscopic procedures. All participants receive 3-L polyethylene glycol (PEG; Klean-Prep, Helsinn Birex Pharmaceuticals Ltd., Dublin, Ireland) for bowel preparation. A split-dose of the PEG preparation is provided. The level of colon cleansing is prospectively evaluated with the Boston Bowel Preparation Scale score.

For participants assigned into the study group, the colonic lumen is washed with saline and the fluid and debris are suctioned as the instrument is slowly inserted from rectum to cecum. Deliberate and systematic inspection of the colonic mucosa is performed with adequate luminal insufflations during both the insertion and withdrawal phases. Polyp size is determined by comparison with open colonoscopic biopsy forceps pushed against the polyp or, in some cases of pedunculated polyp by direct measurement after retrieval. Polyps with size <10mm are removed as they are identified on insertion and withdrawal. Polyps with size ≥10mm are removed only during withdrawal.

For participants assigned into the control group, deliberate mucosal inspection and polyp removal are performed exclusively on instrument withdrawal. During insertion, minimal mucosal inspection and insufflation are applied to efficiently advance the instrument into cecum. If a polyp is found during insertion, investigators are instructed to make a mental note of it and find it during withdrawal for polypectomy.

Inclusion Criteria:

• Aged 45 years or older.
• Agree to participate the study and provide a written informed consent

Exclusion Criteria:

• Previous surgical resection of the colon or rectum
• Inflammatory bowel disease
• Polyposis syndrome
• Previously incomplete colonoscopy
• Obstructive lesions of colon
• Inadequate bowel preparation, defined as Boston Bowel Preparation Scale score of 0 or 1 in any colon segment
• Gastrointestinal bleeding
• Allergy to fentanyl or midazolam
• American Society of Anesthesiology classification of physical status 3 or higher
• Mental retardation
• Pregnancy
• Refusal to provide a written informed consent

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