Adenomas are detected more often in morning than in afternoon colonoscopy.

Objectives: The effectiveness of colonoscopy in preventing colon cancer depends on adenoma detection and removal. Adequacy of bowel preparation, careful mucosal visualization, and adequate withdrawal time are known to affect adenoma detection rate (ADR). Physician fatigue, which usually increases as the day progresses, might impair ADR. The aim of this study is to assess the effect of timing of colonoscopy, morning vs. afternoon, on ADR.
Methods: Medical records of 9,063 colonoscopies performed in 2006 were reviewed for patient demographics, indications, timing, and findings of colonoscopy. Asymptomatic outpatients who had adequate bowel preparation and complete colonoscopy were included. Morning colonoscopies were defined as those that started before 12 noon and afternoon colonoscopies as those that started after 12 noon. ADR is defined as the detection of at least one adenoma per colonoscopy.
Results: A total of 3,619 colonoscopies were included, of which 1,748 (48.3%) were done in the morning and 1,871 (51.7%) were done in the afternoon. ADR was 29.3% in the morning group compared with 25.3% in the afternoon group (P=0.008). There was a trend toward declining ADR for each subsequent hour of the day (P=0.01). In multivariable analysis, colonoscopy in the morning was significantly associated with increased ADR (odds ratio (OR) 1.2 (1.06, 1.4) P=0.006).
Conclusions: Time of performance of colonoscopy seems to be an independent predictor for adenoma detection. ADR was significantly higher in morning colonoscopies than in afternoon colonoscopies. The reasons and implications of this finding should be studied further.