When the inflammation is mainly colonic, distinguishing Crohn’s disease (CD) from ulcerative colitis (UC) is difficult. The paediatric inflammatory bowel disease (PIBD) classes method was created to improve labelling uniformity, however it relied on physician-assigned diagnosis as the criteria standard. The goal of this study was to evaluate the PIBD classes utilising pathology of subsequently resected colon as the criteria standard. A single-center analysis of individuals diagnosed with colonic IBD and treated with colectomy between 2002 and 2017. Baseline pretreatment data were examined, and two reviewers independently utilised the PIBD classes method to provide a label of UC/IBD-unclassified/colonic-CD.  The agreement between the algorithm-based, pre colectomy clinical, and pathologic evaluation of resected colon diagnosis was evaluated. Changes in diagnosis were documented during post colectomy follow-up. Colectomy was performed on 62 children who had medically resistant colonic IBD. Pathologic evaluation of resected colon CD:4;UC:56;IBDU:2 led to the diagnosis. In 51 of 62 individuals, the clinical, PIBD classifications algorithm, and colectomy diagnoses were all consistent. In 58 of 62 individuals, the clinical diagnosis before colectomy was consistent with the colectomy diagnosis. In 51 of 62 patients, the PIBD classes classification corresponded to a colectomy diagnosis. In six patients with PIBD classes labelled IBD-U based on a single class 2 feature, and three patients with PIBD classes labelled CD based on a single class 1 feature, resected colon histology was characteristic of UC.

It is only reasonable to compare the PIBD classes algorithm diagnosis used before colectomy to a diagnostic label based on pathologic inspection of a later resected colon. Caution is advised when applying colonic CD and IBD-U labels based on the presence of a single characteristic.