Variable interpretation of polyp size by using open forceps by experienced colonoscopists

BackgroundEndoscopic measurement of colorectal polyps by using open forceps is commonly used in clinical trials but is subject to several sources of error.ObjectiveAssess error rates in polyp size determination with open forceps at the step of measurement after the forceps are aligned on the polyp.DesignThis was a prospective assessment of 49 gastroenterologists who received training on 10 photographs of polyps with aligned forceps and then measured 10 additional test polyps from photographs. One of the test photographs was excluded because of incorrect forceps alignment.SettingData analyzed at an academic medical center.InterventionPhotographs displayed in a webinar.Main Outcome MeasurementsDescription of rates of accurate measurements, including the fraction correct within 50% and 25% margins of error.ResultsA total of 37% of all measurements were correct to the exact millimeter, 34% were larger, and 29% smaller compared with the reference standard. A total of 47 of 49 doctors measured all 9 polyps within 50% of the reference standard, and 21 measured all 9 correctly within a 25% error margin.LimitationsOther potential sources of error in open forceps measurement were not evaluated.ConclusionOpen forceps polyp size determination is subject to error at the step of using the fully aligned forceps as a scale for measurement. A margin of error of 50% up or down is needed to prevent this step in size determination from causing errors in polyp matching in clinical trials comparing diagnosis-only imaging to colonoscopy.