Adenomas and high-risk lesions were frequently detected on repeat colonoscopy in persons with inadequate bowel preparation on initial screening colonoscopy, suggesting that these lesions were likely missed on initial colonoscopy.

Reena V. Chokshi, MD, of Washington University School of Medicine in St. Louis, Missouri, and colleagues conducted a retrospective chart review of persons who underwent outpatient average-risk screening colonoscopy to the cecum between 2004 and 2009 at an academic medical center. As the investigators reported in Gastrointestinal Endoscopy, 373 patients were identified as having had inadequate bowel preparation during that 5-year span. Of this group, 133 underwent repeat colonoscopy.

The second colonoscopy detected at least 1 adenoma in 33.8% of patients after an average of 340 days between screenings; 31.1% of these patients had had no polyps on initial colonoscopy. The repeat test also detected high-risk states (defined as ≥3 adenomas, ≥1 adenoma, or any adenoma with villous features or high-grade dysplasia) in 18% of patients, with a mean time between colonoscopies of 271 days. No polyps had been seen on initial colonoscopy in 25% of these patients.

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“Because so many of the patients had a follow-up screening less than a year after the initial test, we strongly suspect that most of the precancerous growths found during the second colonoscopy already were present at the time of the initial test,” explained Chokshi in a statement issued by Washington University School of Medicine.

According to the researchers, bowel preparation problems often can be detected within the first few minutes of a colonoscopy. The findings suggest that if the colon is difficult to view due to inadequate bowel prep, the procedure should be stopped and rescheduled.