THE RENAL HISTOPATHOLOGY IN SYSTEMIC VASCULITIS - AN INTERNATIONAL SURVEY STUDY OF INTEROBSERVER AND INTRAOBSERVER AGREEMENT

In order to relate histopathological findings of the kidney in systemi c vasculitis to renal outcome, scoring of various morphological parame ters is necessary. Therefore, we conducted a standardization study for evaluating renal biopsies from patients with systemic vasculitis. Fou r 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 quant itatively (as a percentage of the total number of glomeruli) or dichot omously (on a present/absent scale). Twenty renal biopsies were scored individually by all the observers, from which the inter-observer vari ability 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 satisfacto ry for both rounds (0.55 less than or equal to Kendall's W less than o r 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 a greement for the dichotomous data was poor (kappa less than or equal t o 0.30 in more than half of the parameters in both rounds). Also the d ata 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 sy stem (kappa less than or equal to 0.30 in more than half of the variab les). It is concluded that even between experienced renal pathologists discrepancies occur in scoring kidney biopsies. Inter- and intra-obse rver agreement is greater if a quantitative method for reviewing the b iopsies is applied that requires the observers to score the tissue spe cimens systematically.