Purpose: Recent studies suggest that pre-malignant polyp (PMP) detection rates decrease as the workday progresses. We hypothesized that this effect would be ameliorated by moderating physician daily procedure loads and by utilizing split-dose bowel preparation. Methods: A chart review was performed of ambulatory colonoscopies performed during 2009 at a practice which utilizes conservative procedure scheduling and split-dose bowel preparation. The detection rates of pre-malignant adenomas and serrated polyps by time of day were analyzed. Results: 756 (51%) colonoscopies were performed in the AM and 730 (49%) were performed in the PM. On average, 0.76 PMPs per patient were detected during AM colonoscopies compared with 0.85 during PM colonoscopies (P =0.45). One or more pre-malignant polyps were found in 46% of AM cases versus 48% of PM cases (P=0.8). In an hour-by-hour analysis, PMP detection again did not vary significantly. Bowel preparation outcomes achieved a grade of “excellent” or “good” in 87% of AM cases and 86% of PM cases. Conclusion: The use of split-dose bowel preparation and conservative procedure scheduling can overcome the impact of time of day on the effectiveness of colonoscopy.Table: [1512] Patient demographics and characteristics of colonoscopiesTable: [1512] Pre-malignant polyp detection by histology and time periodFigure: [1512] Frequency distribution of pre-malignant polyps (PMPs) per colonoscopy by time period (AM vs. PM). Each bar depicts the percentage of colonoscopies in which 0, 1, 2, 3, or ≥4 PMPs were removed and confirmed histologically. PMPs are defined as any of the following polyp types: adenomatous, serrated lesion or hyperplastic >10 cm.Figure: [1512] Frequency distribution of bowel preparation quality by time period (AM vs. PM). Each bar depicts the percentage of total patients with designated bowel preparation quality, measured by the endoscopist on a non-validated, four point scale. Note: All colonoscopies meeting inclusion and exclusion criteria prior to procedure are included (n=1501).