P349 Faecal Calprotectin in Ulcerative Colitis - Associations with Mucosal Inflammatory Activity and Disease Extent

Abstract Background In ulcerative colitis (UC), faecal calprotectin (FC) correlates with endoscopic severity and disease extent, and low levels are associated with histological remission [1, 2]. The effect of mucosal inflammatory activity versus disease extent on the FC levels, remains poorly understood. We aimed to compare FC levels in patients grouped by endoscopic and histologic scores of the inflammatory activity. We also grouped patients according to active disease extent based on endoscopic or histological evaluations. Methods This was a post hoc analysis of patients diagnosed with UC or with confirmed UC at Stavanger University Hospital, Norway, from 2012 to 2020. Visits were performed at diagnosis, and after 3 and 11 months. FC was analysed in samples collected from 4 weeks before until 3 days after visits (EliA Calprotectin or EliA Calprotectin 2, Thermo Scientific). At each visit, colonoscopy was performed, and biopsies were collected from three colorectal segments (rectum, left colon, right colon). Mucosal inflammatory activity was scored endoscopically by Mayo Endoscopic Score (MES 0 – 3) and histologically by Nancy Histological Index (NHI 0 – 4). The highest value of the segmental NHI scores were reported. Disease extent was defined by Montreal classification. Distribution of acute inflammation was defined by the number of colorectal segments with NHI ≥ 2 (presence of neutrophilic infiltrates). Results In total 554 visits of 249 patients were analysed. FC levels increased significantly for every stepwise increase in MES, and median FC was 30-fold (range 19-49) higher in MES 3 than in MES 0 subgroups. The largest difference was observed between MES 1 and MES 2 (Figure 1a). FC levels also increased significantly for every stepwise increase in NHI, except between NHI 3 and NHI 4. Median FC level was 54-fold higher in NHI 4 group compared with the NHI 0 group, and the largest difference was observed between NHI 1 and NHI 2 (Figure 1b). Disease extent showed little effect on FC, and significant difference was only observed between proctitis and pancolitis with 3-fold (range 1.6 – 4.5) higher levels in the latter groups (Figure 2a). Median FC level was 3-fold higher in patients with acute inflammation in all 3 segments compared to patients with acute inflammation in only 1 colorectal segment (Figure 2b). Conclusion FC increased significantly by increasing mucosal inflammatory activity, whereas disease extent showed a modest effect on the FC levels. FC is an accurate and useful biomarker of both endoscopic and histological inflammatory activity in patients with ulcerative colitis. References: 1. Kawashima K. et al, BMC Gasteroenterology 2016 2. Magro F. et al, Gut 2019