Some patients felt no pain or only mild discomfort with the unsedated colonoscopy. However, unsedated colonoscopy was thought to be an option for some but not for all. If we could able to identify which patients at high risk for painful colonoscopy in preoperational stage, targeted administration of sedatives or special techniques to these patients would be an attractive option.

Here we prospectively collected the data during colonoscopy and investigated the possible risk factors associated with painful colonoscopy by using a step-wise multivariate regression model. Furthermore we developed a novel point score to predict whether the patients at high risk for painful colonoscopy and targeted offer an appropriate method of colonoscopy or with the aid of special techniques to help the completion of procedure.

Inclusion Criteria:

• patients who underwent unsedated colonoscopy

Exclusion Criteria:

• (1) no bowel preparation or colon cleansing by enema only; (2) no need to reach cecum; (3) prior finding of severe colon stenosis or obstructing tumor; (4) history of colectomy; (5) unstable hemodynamics; (6) pregnant; (7) unable to give informed consent.

All patients were prescribed polyethylene glycol electrolyte for bowel preparation according to the preference of physicians. They were asked to drink the first 2L of PEG4000e at19:00-20:00 PM on the night before colonoscopy within 2 hours. Then, on the day of the examination, patients were asked to take the remaining 2L 5 hours before the procedure. Patients were encouraged to drink more clear liquids after purgatives for adequate hydration before colonoscopy. In addition, patients were instructed to have a regular meal for lunch and only liquid diets for dinner the day before the operation.