In the tailored group, high-risk patients are instructed to drink the first 2 L of Polyethylene Glycol (PEG) at 19:00-21:00 hours on the day before colonoscopy at a rate of 250 ml every 15 min. On the day of the procedure, they take another 2 L PEG 4-6 h before colonoscopy. The low-risk patients were given a standard dose of 2 L PEG 4-6 h before colonoscopy.

In the control group, all the patients drink single dose of 2 l Polyethylene Glycol (PEG) 4-6 h before colonoscopy at a rate of 250 ml every 15 min.

In the Tailored group, high-risk people are given intensified bowel preparation regimens, low-risk people are given routine regimens.

In the control group, all the patients are given routine regimens.

The quality of bowel preparation is evaluated using BBPS.

The proportion of patients from whom at least one adenoma can be detected.

The proportion of patients from whom at least one polyp can be detected.