Introduction Knowing if polyps are larger than 10mm is critical when determining colonoscopic surveillance strategies. Judging polyp size from the endoscopic view alone becomes important if polyps are not retrieved intact. Strategies based on deliberately discarding small polyps rely on accurate discrimination of polyp size but little is known about endoscopists ability to make this judgement. Our aim is to assess the accuracy of polyp size estimation using a novel in vitro model, comparing different professional groups and use of accessories to improve estimates.

Methods Nine endoscopists (3 consultants, 3 trainees and 3 nurse endoscopists) judged the size of 15 “polyps” made from modelling clay (size range 6–36 mm) placed inside a colonoscopy training model (Koken Co Ltd, Tokyo). Polyps of different sizes were presented in random order. Size estimates were made using endoscopic visual assessment alone or by comparing the polyp to biopsy forceps or a 10 mm snare. A degree of confidence for each guess was recorded.

Results Consultants and trainees were significantly better than nurse endoscopists at judging whether the model polyps were larger or smaller than 10 mm (91.8% vs 79.2% p<0.05). Overall, visual assessment alone had an accuracy of 78.8%. Inaccuracy was largely due to underestimation of size. Use of accessories improved discrimination around the 10 mm threshold (p<0.05). The snare produced slightly better accuracy (87.9%) than forceps (83.8%) (NS). All professional groups expressed similar degrees of confidence in their estimates.

Conclusion In this model, medical endoscopists were better than nurse endoscopists in assessing the size of polyps. This may be because nurses in our study do not routinely perform polypectomy whereas doctors have all had the opportunity to learn from comparing the size of resected polyps with their original endoscopic assessment. Use of biopsy forceps or a snare improved size estimation and these may be helpful tools when teaching this important aspect of polyp assessment in vivo.

Competing interests J Geraghty Grant/Research Support from: Cook Medical, Z Raisi-Estabragh: None declared, M Gillon: None declared, P O'Toole: None declared, S Sarkar: None declared.