PTU-62 Microscopic colitis: Finding the sweet spot

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Introduction Microscopic colitis (MC) is a prevalent and treatable cause of chronic, non-bloody, watery diarrhoea. In MC, the colon is usually macroscopically normal therefore the BSG and European guidance call for right and left colon biopsies to be taken for histological examination to make the diagnosis. There is no established guidance on biopsy protocol. This retrospective, multi-centre study looked at our biopsy practice and whether there is a pattern that leads to higher diagnostic yield for diagnosis of MC. Methods The endoscopy reporting systems in six trusts across Kent, Surrey, Sussex and Cambridge were searched for all colonoscopies in patients aged 18 or over with the indication chronic diarrhoea performed between 1 January 2020 and 31 March 2020. All diagnosis of cancer or macroscopic inflammatory disease were excluded. The endoscopy and histology reports were analysed to see how many biopsies were taken and their histological diagnosis. Results 363 reports were analysed. The age range was 18 to 90. Male to female ratio was 1:1.8. Biopsies were taken from both the right and left colon in 83.5%. Biopsies of the rectum were taken in 10.5%. The number of biopsies taken ranged from 0 to 17, most commonly taken as 4 right and 4 left colon biopsies (18.5%). The most common distribution was random right and left colon biopsies (22%) followed by colonic series biopsies* (9.6%). The diagnosis of MC was made in 20 cases. The age distribution was 30 to 80 (median 67.5) with male to female ratio 3:7. All had biopsies taken from both right and left colon amounting to 3 to 13 biopsies in total. The most common biopsy pattern in those diagnosed with MC were 5-6 biopsies taken as colonic series (25%) or 2-4 biopsies taken from both right and left colon (45%). Distribution in number of biopsies is shown in Table 1. Conclusion There was a large variation in the sites and number of biopsies taken to investigate for MC reflecting the lack of established guidance on biopsy protocol. Excessive biopsy samples have negative impacts on our green footprint, increase workload for histopathology colleagues and potential risk in bleeding and perforation risk for patients. We propose that the BSG should implement MC diagnostic biopsy protocol for standardisation of our practice. From the results of our data we advocate for either 5-6 biopsies as a colonic series or 2-4 biopsies to be taken from both right and left colon. Biopsies should not be taken from the rectum in a macroscopically normal colon. *Multiple biopsies ordered from proximal to distal colon

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