Background: Bowel preparation quality scales are used to document the superiority of one preparation regime vs. another. The validity and reliability of these scales are not routinely stated in reports of studies in which the scales are used. A new colonoscopy bowel preparation scale (the Ottawa bowel preparation scale) was developed and validated prospectively.
Methods: Ninety-seven consecutive patients undergoing elective outpatient colonoscopy were entered into the study. The quality of the bowel preparation was assessed independently by two investigators who used the Ottawa scale, and the only other validated scale (Aronchick scale) that could be identified. The interobserver agreement and reliability of each scale was assessed by the Pearson correlation coefficient (r), the intraclass correlation coefficient, and regression analysis.
Results: The Pearson correlation coefficients were, respectively, 0.89 and 0.62 for the Ottawa and Aronchick scales (p<0.001). The values for the kappa statistic, an intraclass correlation coefficient measuring agreement over and above chance agreement, were, respectively, 0.94 and 0.77 (p<0.001). Linear regression analysis, mapping the line best describing the scatter of scores by raters, for the Ottawa scale revealed a slope of the line of 0.93 and a y intercept of 0.10. The Aronchick scale revealed a slope of 0.65 and a y intercept of 0.46. The Ottawa scale thus was closer to an identity line comparing raters (i.e., closer to a line with slope of 1.00 and y intercept of 0.00). The Ottawa scale demonstrated a right colon kappa (intraclass correlation coefficient) of 0.92: 95% CI[0.88, 0.95], a mid colon kappa (intraclass correlation coefficient) of 0.88: 95% CI[0.82, 0.92], and a rectosigmoid kappa (intraclass correlation coefficient) of 0.89: 95% CI[0.83, 0.92].
Conclusions: The Ottawa scale was validated prospectively and demonstrates high interobserver agreement and reliability, whether used as a total score or for individual colon segments.