Introduction Polyp size is a principal factor used to determine surveillance intervals both nationally and internationally, and is an independent risk factor for the malignant potential of colorectal lesions. There is uncertainty regarding the most accurate method of measurement of colonic polyps, between the in situ and post-formalin fixation measurements. This study aims to determine the preferred polyp measurement for use in determining surveillance intervals and compare post-fixation polyp measurements using three different devices.
Methods 107 consecutive colorectal polyps were measured in situ, pre-fixation and post-fixation to the nearest millimetre. Post-fixation measurements were recorded using a metal ruler, callipers and a graduated magnifying lens. One sample t-tests and the Kruskall–Wallis test were used for data analysis.
Results Pre-fixation ruler measurements were significantly higher than both in situ and post-fixation ruler measurements (p<0.05). However no significant difference was observed between in situ and post-fixation measurements (p=0.36). In situ measurements were associated with a higher rate of surveillance group variation than post-fixation measurements (9.3% vs 5.6%). No significant difference was seen between measurements obtained by the three different devices post-fixation (p=0.89).
Conclusion Post-fixation polyp size measurements are associated with lower rates of surveillance variation and may be considered the preferred measurement. On average colonoscopists underestimated polyp size. In the absence of a clinically significant difference between measurement devices, we advise the ruler be used for post-fixation measurements due to its widespread availability.
Competing interests None declared.