Background Assessment of disease activity in UC is important for designing an optimal therapeutic strategy. No single histology score is considered optimum. The aim of this study was to compare intraobserver reproducibility and the interobserver agreement of available histological UC activity indexes.

Methods One hundred and two biopsy specimens (collected between 2003 and 2014) were scored blindly by three pathologists by determining Geboes, Riley, Gramlich and Gupta indexes and global visual evaluation (GVE). Intraobserver reproducibility and interobserver agreements for index and items of index were studied by intraclass correlation coefficient for quantitative parameter and by κ values and Krippendorff index for qualitative parameters. Relationship between indexes was studied by computation of Pearson's and Spearman's correlation coefficients.

Results Geboes, Riley, Gramlich and Gupta indexes and GVE showed good intraobserver reproducibility and a good interobserver agreement. Histological items that showed the best interobserver agreement were ‘erosion/ulceration or surface epithelial integrity’ and ‘acute inflammatory cells infiltrate/neutrophils in lamina propria’. The five scores were strongly correlated.

Conclusions Correlation between indexes is strong. Intraobserver reproducibility and interobserver agreement for all indexes is very good. Histological items that showed the best interobserver agreement are ‘erosion/ulceration’ and ‘acute inflammatory cells infiltrate/neutrophils in lamina propria’.