Nancy histological index in ulcerative colitis: an interobserver study

The Nancy histological index (NHI) is a measure of disease activity within colorectal biopsies and a predictor of clinical outcome in ulcerative colitis (UC). We measured interobserver agreement (IOA) during NHI scoring of 20 colorectal biopsies in UC by 13 pathologists of varying grade and experience. The level of IOA was measured using Fleiss' kappa statistic. The degree of IOA was moderate, with kappa scores of 0.53 (SE 0.01) for the whole group (n=13), 0.50 (SE 0.05) for the consultants (n=4) and 0.54 (SE 0.019) for the trainees (n=9). Normal biopsies or those showing a mild increase in lamina propria chronic inflammation were graded most reproducibly. Subjectivity existed at NHI grade boundaries, particularly identification of mild acute inflammation (AI), assessment of AI severity and identification of ulceration. An education programme for pathologists or an artificial intelligence tool may improve IOA in the future.