Interobserver Agreement Using Histological Scoring of the Canine Liver

BACKGROUND: Grading schemes for the assessment of hepatic fibrosis and necroinflammatory activity in humans previously have been applied to dogs with chronic hepatitis. Interobserver agreement is a desirable characteristic for any histological scoring scheme. HYPOTHESIS/OBJECTIVES: To assess interobserver agreement associated with pathologists using a previously published histological scoring scheme to assess hepatic fibrosis and necroinflammatory activity in dogs and to compare fibrosis scores assigned to serial sections stained with hematoxylin & eosin (H&E) and picrosirius red. ANIMALS: Histological sections of liver from 50 dogs with variable degrees of hepatic fibrosis and necroinflammatory activity were selected from institutional tissue archives. METHODS: Six board‐certified veterinary anatomic pathologists assigned fibrosis and necroinflammatory activity scores to the histological sections. The multiuser kappa statistic was calculated to assess interobserver agreement. Fibrosis stage assigned to serial sections stained with picrosirius red and H&E was compared using the Wilcoxon signed‐rank test. RESULTS: Multiuser kappa statistics for assessment of fibrosis and necroinflammatory activity from H&E‐stained sections were 0.35 and 0.16, respectively. There was no difference in median fibrosis scores assigned to serial section stained with H&E and picrosirius red (P = .248). CONCLUSIONS AND CLINICAL IMPORTANCE: There was fair interobserver agreement when pathologists assessed fibrosis and poor agreement when they assessed necroinflammatory activity. This suboptimal agreement must be taken into account by clinicians making decisions based on histology reports of the liver and in the design of studies evaluating these findings. To decrease this variability, ideally >1 pathologist should evaluate each section.