Validation of the Montreal Bowel Preparation Scale: An Auditable Application of the MSTF Guidelines

Introduction: Existing bowel preparation scales (BPS) are limited in their ability to predict interval to next colonoscopy. The US Multi-society task force (MSTF) recommends that screening or surveillance colonoscopies be repeated within the year if the preparation does not allow for detection of polyps greater than 5mm in size. We assessed the reliability and validity of a new BPS - the Montreal BPS (MBPS) - in comparison with the Boston BPS (BBPS). Methods: We developed the 5mm MBPS: score = 1 - preparation being adequate to detect lesions ≥5mm on combination of insertion and withdrawal after washing; score = 0 - preparation being inadequate to detect lesions ≥5mm; and U - being unable to complete the colonoscopy for reasons other than the preparation. In an exploratory analysis, we also applied the same definition using a cut-off of 3mm (3mm MBPS). We retained two possible definitions of adequate BBPS scores based on published studies: total score ≥5 (BBPS 5) or each segment score ≥2 with a total score ≥6 (BBPS 2-6). Video recordings of 83 colonoscopies were independently evaluated by nine physicians (seven staff gastroenterologists and two senior gastroenterology fellows) using the BBPS, 5mm MBPS and 3mm MBPS. Eight of these videos were evaluated twice, one year apart, to assess intra-rater agreement. Weighted kappas quantified intra- and inter-rater agreements. Associations between scores and clinical outcomes were assessed. Results: 72.3% of colonoscopies were performed for screening or surveillance. Inter- and intra-rater agreements for each scale are shown in Table 1. Associations between scores and clinical outcomes are shown in Table 2. Though arithmetic trends were noted, associations for these clinical outcomes lacked statistical significance.Table 1: Inter- and intra-rater agreementTable 2: Association between scores and clinical outcomesConclusion: For all scales, intra-rater agreement was superior to inter-rater agreement. Inter-rater agreements were lower than expected with at best moderate agreement. This may reflect the dichotomized interpretation of the scales (adequate vs inadequate) contrary to previous studies which compared scores assessed as continuous variables. The MBPS appears promising but further studies are required to assess how to best operationalize the US MSTF recommendations for interval to the next colonoscopy based on bowel cleanliness.

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