Objectives: Withdrawal time (WT) has been proposed as a quality indicator for colonoscopy based on evidence that it is directly related to the rate of adenoma detection. Our objective was to test the hypothesis that baseline WT is inversely associated with the risk of finding neoplasia at interval colonoscopy. Methods: In all, 3,121 subjects, aged 50-75 years, had screening colonoscopy between 1994 and 1997 at 13 Veteran Affairs Medical Centers. In all, 1,193 subjects returned by protocol for surveillance within 5.5 years. In the 304 patients without polyps at baseline, we evaluated the contribution of baseline WT to their risk of interval neoplasia using bivariate and logistic regression analysis. We also examined the correlation between mean WT, baseline adenoma detection rate, and interval neoplasia rate at the medical-center level. Results: The average WT at the baseline exam in subjects with neoplasia on follow-up was 15.3 min as compared with 13.2 min in subjects without neoplasia (P=0.18). In a logistic regression model, WT was not associated with the risk of interval neoplasia (P=0.07). At the medical-center level, mean WT was not correlated with the probability of finding interval neoplasia (P=0.61) but was positively correlated with adenoma detection rate at baseline (P=0.03). Conclusions: In this study with a mean baseline WT >12 min, there was no detectable association between WT and risk of future neoplasia. The medical center-level WT was positively correlated with adenoma detection. Therefore, above a certain threshold, WT may no longer be an adequate quality measure for screening colonoscopy.
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