According to an American study, the results of which were published in June 2011, suboptimal bowel preparation is associated with a substantially lower efficacy of colonoscopy to detect adenomas. This in turn demonstrated the need for early patient follow up after each treatment.
"We aimed to identify factors associated with the decision to repeat the examination early after a colonoscopy done with suboptimal bowel preparation," said lead author Benjamin Lebwohl from Columbia University Medical Centre in New York. "We also aimed to quantify adenoma miss rates among those pairs of colonoscopies separated by an interval shorter than the time suggested by current guidelines, which assume an optimal bowel preparation."
At a single hospital-based endoscopy unit, the quality of bowel preparation was recorded in 12,787 patients undergoing colonoscopy. Of 3047 patients (24%) in whom preparation quality was poor or fair, 505 patients (17%) underwent subsequent colonoscopy in less than 3 years.
Patients who had early subsequent colonoscopy were more likely to have lack of cecal intubation on the first procedure (odds ratio [OR], 3.62; 95% confidence interval [CI], 2.50 - 5.24) and to have had a polyp found on the first procedure (OR, 1.55; 95% CI, 1.17 - 2.07).
On the subsequent colonoscopy, 216 of 505 patients had optimal preparation. Of 198 adenomas identified on the second procedure, 83 were not visualized on the initial procedure. This finding yielded an adenoma miss rate of 42% overall (95% CI, 35 - 49), with an advanced adenoma miss rate of 27% (95% CI, 17 - 41). When colonoscopy was repeated in less than 1 year (n = 86), the adenoma miss rate was 35% overall, and 36% for advanced adenomas.
"Although a minority of patients undergo early repeat examination after colonoscopies done with suboptimal bowel preparation, the miss rates for colonoscopies done with suboptimal bowel preparation were high, suggesting that suboptimal bowel preparation substantially decreases colonoscopy effectiveness and may mandate an early follow-up examination," the study authors write.
Limitations of this study include the fact that it was based around a single-centre which leads to a possibility of selection bias, and retrospective design.
"Our findings of a miss rate of 42 percent for all adenomas and 27 percent for advanced adenomas suggest that suboptimal bowel preparation has a substantial harmful impact on the effectiveness of colonoscopy, and follow-up examination within one year should be considered," Dr. Lebwohl concluded. "Because neoplastic findings on the initial colonoscopy were associated with a greater miss rate, a repeat examination within one year is indicated when an adenoma is found during a colonoscopy with suboptimal bowel preparation."
