Pathological classification of anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis.

What drives human beings to classify? It seems as if it is within our nature to do so. Clinical classification systems for the systemic vasculitides were composed a long time ago, and they are constantly being revised and altered. The histopathological features of many diseases are so diverse that classification is called for. The histopathological classification for anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis was the culmination of results produced from a number of clinicopathological studies conducted within the European Vasculitis Study Group (EUVAS). The classification scheme has four general categories, named focal, crescentic, sclerotic and mixed. The first three categories are based on the predominance of normal glomeruli, glomeruli with cellular crescents and globally sclerotic glomeruli. The mixed category represents a heterogeneous phenotype of biopsies in which none of the aforementioned features is dominant. Results from a validation study incorporating 100 patients with at least 1-year follow-up showed that the phenotypical order of the four classes corresponded to the severity of renal function impairment. The new histopathological classification for ANCA-associated glomerulonephritis provides a logical structure for the categorization of patients into four subgroups defined according to glomerular features. This classification will be of use for future studies, such as clinical trials.