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To determine the maximum rate of false-positive diagnoses that patients and health care professionals were willing to accept in exchange for detection of extracolonic malignancy by using computed tomographic (CT) colonography for colorectal cancer screening.After obtaining ethical approval and informed consent, 52 patients and 50 health care professionals undertook two discrete choice experiments where they chose between unrestricted CT colonography that examined intra- and extracolonic organs or CT colonography restricted to the colon, across different scenarios. The first experiment detected one extracolonic malignancy per 600 cases with a false-positive rate varying across scenarios from 0% to 99.8%. One experiment examined radiologic follow-up generated by false-positive diagnoses while the other examined invasive follow-up. Intracolonic performance was identical for both tests. The median tipping point (maximum acceptable false-positive rate for extracolonic findings) was calculated overall and for both groups by bootstrap analysis.The median tipping point for radiologic follow-up occurred at a false-positive rate greater than 99.8% (interquartile ratio [IQR], 10 to >99.8%). Participants would tolerate at least a 99.8% rate of unnecessary radiologic tests to detect an additional extracolonic malignancy. The median tipping-point for invasive follow-up occurred at a false-positive rate of 10% (IQR, 2 to >99.8%). Tipping points were significantly higher for patients than for health care professionals for both experiments (>99.8 vs 40% for radiologic follow-up and >99.8 vs 5% for invasive follow-up, both P < .001).Patients and health care professionals are willing to tolerate high rates of false-positive diagnoses with CT colonography in exchange for diagnosis of extracolonic malignancy. The actual specificity of screening CT colonography for extracolonic findings in clinical practice is likely to be highly acceptable to both patients and health care professionals. Online supplemental material is available for this article.

Original publication




Journal article



Publication Date





144 - 152


From the Centre for Medical Imaging, Podium Level 2, University College Hospital, 235 Euston Rd, London, NW1 2BU, England (A.A.P., D.B., H.F., E.H., N.B., S.A.T., S.H.); Department of Epidemiology and Public Health, University College London, London, England (A.G., C.V.W.); Department of Primary Care Health Sciences (S.M.) and Centre for Statistics in Medicine (D.G.A.), University of Oxford, Oxford, England; Department of Public Health and Epidemiology, Birmingham University, Birmingham, England (S.Z., R.L.); and Faculty of Medicine, University of Southampton, Southampton, England (G.L.Y.).


Humans, Colorectal Neoplasms, False Positive Reactions, Colonography, Computed Tomographic, Incidental Findings, Aged, Aged, 80 and over, Middle Aged, Early Detection of Cancer, Surveys and Questionnaires