Background: Endoscopy and histopathology are pivotal techniques for evaluating disease activity in ulcerative colitis (UC). Validated endoscopic   and histological indices   have only recently been published and their correlation has not yet been examined. We aimed to correlate the Ulcerative Colitis Endoscopic Index of Severity (UCEIS) with the Nancy and Robarts' histological indices in patients with established UC.
Methods: Retrospective cohort study at a single centre on patients with an established diagnosis of UC who underwent flexible sigmoidoscopy or colonoscopy by a single clinician (ST) between March 2013 and August 2015. The UCEIS was recorded at the worst affected area in the left colon and mucosal biopsies taken from this and other areas. Histological disease activity using the Nancy (NI) and Robarts' (RHI) histological indices was scored by a specialist pathologist (LMW) blinded to the endoscopy report. Spearman correlation and area under the curve (AUC) between the UCEIS, NI and RHI, and between NI and RHI was performed.
Results: 125 patients were included in the study with a median age of 37 years (range 16–81 years), 64/125 (51%) male, and a wide distribution of UCEIS (scale 0–8): 0=21; 1–3=48; 4–6=51; 7–8=5. The correlation coefficient (r) between the UCEIS and NI (scale 0–4) was 0.84 (95% CI 0.76–0.89, p<0.001) and between UCEIS and RHI (scale 0–33) was 0.86 (95% CI 0.80–0.90, p<0.001), as shown in figure 1. The difference in correlation was not significant (p=0.57). When UCEIS=0, there was no microscopic activity in 20/21 (95%, NI 0–1) and 18/21 (86%, RHI 0–3). When UCEIS=1, microscopic inflammation was absent in 20/28 (71%) and 18/28 (64%) respectively (p<0.05). Quiescent disease activity defined as the absence of neutrophils (NI 0–1, RHI 0–3) was more closely correlated with UCEIS=0/8 than with UCEIS=1/8. AUC=0.71 for RHI and AUC=0.65 for NI. There was excellent correlation between the two histological indices (r=0.92, 95% CI 0.87–0.95, p<0.001), but the NI was considered (by LMW) easier to score.
Conclusions: The UCEIS shows strong correlation with both Nancy and Robarts' histological indices. Complete mucosal healing is best defined as a UCEIS 0/8, since this correlates most closely with the absence of microscopic disease activity.
 Travis SP, Schnell D, Krzeski P, et al. (2013), Reliability and initial validation of the Ulcerative Colitis Endoscopic Index of Severity (UCEIS). Gastroenterology, 145(5):987–995
 Travis SP, Schnell D, Krzeski P, et al. (2012), Developing an instrument to assess the endoscopic severity of ulcerative colitis: the Ulcerative Colitis Endoscopic Index of Severity (UCEIS). Gut, 61(4):535–542
 Marchal-Bressenot A, Salleron J, Boulagnon-Rombi C, et al. (2015), Development and validation of the Nancy histological index for UC. Gut, 0:1–7, doi:10.1136/gutjnl.2015.310187
 Mosli MH, Feagan BG, Zou G, et al. (2015), Development and validation of a histological index for UC. Gut, 0:1–9, doi:10.1136/gutjnl.2015.310393