Colonoscopy is now the most recommended screening method for colorectal cancer in primary-care offices (Am J Prev Med. 2009;37:8-16). Colonoscopies done in the morning appeared to detect more adenomas, a potentially cancerous colon polyp, than those procedures performed in the afternoon.

Study investigators reviewed medical records for 1,748 completed colonoscopies that started before noon and 1,871 that started after noon at the Cleveland Clinic throughout 2006. The adenoma detection rate (ADR) was 29.3% in the morning group of patients compared with 25.3% in the afternoon group, with fewer adenomas detected as the day progressed (Am J Gastroenterol. 2009;104: 1659-1664).

The mean age of patients was similar in the morning and afternoon groups, but morning testing included a significantly higher number of women, patients with personal and family histories of colonic neoplasia, and patients with diverticulosis. As in other studies, advancing age, male gender, and a personal history of adenomas were associated with higher adenoma detection. Researchers also found the absence of diverticulosis to be associated with higher ADR, although they are unsure why this would be.

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Potential explanations for the 4% difference in morning and afternoon ADRs include physician fatigue, which usually increases as the day progresses; diminished attentiveness or vigilance on the part of the endoscopist in the afternoons; and the possibility that the examiner might not have spent as much time during the withdrawal phase in the afternoon procedures as in the morning procedures. n