Morning colonoscopies are associated with improved adenoma detection rates.

Background: Higher adenoma detection rates are associated with decreased risks for subsequent colorectal cancers. Studies have suggested that adenoma detection rate (ADR) may be affected by timing of colonoscopy due to endoscopist fatigue later in the day. The aim of our study is to assess the influence of the timing variables on ADR.

Methods: Univariate analysis and multivariate logistic regression analysis were performed on a prospective colonoscopy database, comparing ADR for colonoscopies performed in the morning shift (AM) and in the afternoon shift (PM) over a 1-year period. Each shift lasted 4 h. Only elective outpatient completed colonoscopies with adequate bowel preparation, performed by four certified staff endoscopists, were included. Surveillance colonoscopies for cancers were excluded. ADR was defined as the detection of at least one histologically confirmed polyp during colonoscopy.

Results: A total of 533 colonoscopies were included. ADR was 25 % in the cohort. Mean age was 59 (SD 14.1). Two hundred and seventy (50.6 %) were done in the AM and 263 (49.4 %) were done in the PM. ADR was 29 % in the AM group compared to 21 % in the PM group (p = 0.03). Excluding time needed for polypectomy, the mean time taken for scope withdrawal was significantly longer in the morning group (12 min) compared with the afternoon group (10 min) (p = 0.002). The longer withdrawal time in the morning was significantly associated with increased ADRs (OR 1.104, 95 % CI 1.063-1.147) (p < 0.0001).

Conclusion: Timing of colonoscopy is an independent predictor for ADR. Colonoscopies performed in the morning have a longer mean withdrawal time, thus leading to a significantly higher ADR. As endoscopists concentration decreases as the day progresses, this may account for the shorter time spent on colonoscopies on the afternoon.