Background & Aims: If computed tomographic colonography (CTC) is used for primary colorectal cancer (CRC) screening with a small polyp size threshold to define a CTC study as positive, a substantial portion of all colonoscopies performed annually will be to follow up positive CTC examinations. Moreover, the majority of positive CTC examinations would be false positives (FP). This case-control study was undertaken to test the hypothesis that colonoscopy examinations resulting from FP CTC studies would take longer to complete than negative screening colonoscopies. Methods: Endoscopic records of a large, urban hospital were reviewed to identify all patients who had either a positive barium enema (BE) study or flexible sigmoidoscopy (FS) and a negative follow-up colonoscopy examination (these patients were used as surrogates for CTC FP cases). For each of the 28 FP patients or cases identified, 2 screening colonoscopies performed by the same endoscopist within the same time period were identified and used as matched controls. A two-way analysis of variance test was performed to assess for differences in time to complete colonoscopies between these 2 groups, controlling for the individual endoscopist. Results: FP colonoscopies took an average of 24.0 minutes to complete, whereas negative screening colonoscopies took 14.9 minutes; FP colonoscopies required 61% more active time to complete. This highly statistically significant difference (P < .0001) persisted with subset analyses that only included BE or FS cases and when fellow or surgeon cases were excluded. Conclusions: FP colonoscopies take longer to perform than negative screening colonoscopies. If CTC is implemented as the primary modality for CRC screening, these FP examinations could comprise a substantial percentage of the colonoscopies performed, potentially leading to a significant decrease in endoscopic productivity.
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