Meta-Analysis of the Effect of Bowel Preparation on Adenoma Detection: Early Adenomas Affected Stronger than Advanced Adenomas

BACKGROUND AND AIMS Low-quality bowel preparation reduces efficacy of colonoscopy. We aimed to summarize effects of bowel preparation on detection of adenomas, advanced adenomas and colorectal cancer. METHODS A systematic literature search was performed regarding detection of colonic lesions after normal and low-quality bowel preparation. Reported bowel preparation quality was transformed to the Aronchick scale with its qualities "excellent", "good", "fair", "poor", and "insufficient" or "optimal" (good/excellent), "suboptimal" (fair/poor/insufficient), "adequate" (good/excellent/fair) and "inadequate" (poor/insufficient). We identified two types of studies: i) Comparative studies, directly comparing lesion detection according to bowel preparation quality, and ii) repeat colonoscopy studies, reporting results of a second colonoscopy after previous low-quality preparation. RESULTS The detection of early adenomas was reduced with inadequate vs. adequate bowel preparation (Odds Ratio (OR) 0.53, CI: 0.46-0.62, p<0.001). The advanced adenomas were affected less in comparison (0.74, CI: 0.62-0.87, p<0.001). The large number of subjects considered in the present meta-analysis resulted in smaller confidence intervals compared to earlier studies. Classifying the bowel-preparation quality as suboptimal vs. optimal led to the same qualitative conclusion (OR: 0.81, CI: 0.74-0.89, p<0.001 for early adenomas, OR: 0.94, CI: 0.87-1.01, n.s. for advanced adenomas). Bowel preparation was equally important for right-sided/ flat/ serrated vs. other lesions in most observational studies but more relevant in some repeat colonoscopy studies; data regarding carcinoma detection were insufficient. CONCLUSION Inadequate bowel preparation affects detection of early colonic lesions stronger than advanced lesions.