The renal histopathology in systemic vasculitis: An international survey study of inter- and intra-observer agreement

In order to relate histopathological findings of the kidney in systemic vasculitis to renal outcome, scoring of various morphological parameters is necessary. Therefore, we conducted a standardization study for evaluating renal biopsies from patients with systemic vasculitis. Four experienced renal pathologists from four European centres joined in the study. A scoring protocol was devised that required the observers to score an extensive number of histopathological lesions either quantitatively (as a percentage of the total number of glomeruli) or dichotomously (on a present/absent scale). Twenty renal biopsies were scored individually by all the observers, from which the inter-observer variability was analysed. Ten randomly chosen biopsies were scored again, in order to obtain the intra-observer variability. For inter-observer agreement, the evaluation of the quantitative variables was satisfactory for both rounds (0.55 less than or equal to Kendall's W less than or equal to 0.95 and 0.59 less than or equal to W less than or equal to 0.96, respectively, with all P < 0.05). However, the inter-observer agreement for the dichotomous data was poor (kappa less than or equal to 0.30 in more than half of the parameters in both rounds). Also the data on intra-observer agreement showed more favourable results for the analysis of the quantitative data (Pearson's r > 0.45 in more than 85% of the variables in both rounds) than for the dichotomous scoring system (kappa less than or equal to 0.30 in more than half of the variables). It is concluded that even between experienced renal pathologists discrepancies occur in scoring kidney biopsies. Inter- and intra-observer agreement is greater if a quantitative method for reviewing the biopsies is applied that requires the observers to score the tissue specimens systematically.