Reproducibility of the WHO classification of glomerulonephritis

The inter-observer variation of the WHO classification of glomerulonephritis (GN) was studied using Kappa statistics. One hundred renal biopsies were selected with almost equal representation of the following types of GN: minimal change nephropathy, membranous GN, focal proliferative GN, diffuse mesangial proliferative GN, endocapillary GN, membranoproliferative GN, and crescentic GN. Slides stained with silver-methenamine and PAS-hematoxylin were circulated among the members of the panel, who made their diagnoses without knowing those of the other participants and without knowledge of the clinical conditions. There was a very good overall diagnostic agreement of 0.67 with a Kappa value of 0.61, figures which compete very well with other diagnostic systems analysed with Kappa statistics. Analysing the single types of GN, we found that the highest Kappa values were obtained for crescentic GN (0.81), endocapillary GN (0.79) and membranous GN (0.74) and the lowest Kappa values for membranoproliferative GN (0.40) and diffuse mesangial proliferative GN (0.44). Basically, the international classification of GN is founded upon light microscopy. Our results demonstrate that this system works generally well. The diagnostic reproducibility of the types with less satisfactory Kappa values can be expected to be improved by including immunopathology and electron microscopy.