We are all relatively familiar with the WHO classification system for lupus nephritis, which gives nephrologists a relatively good idea of renal prognosis based on the histologic findings of renal biopsy.
A similar type of system has been developed for IgA Nephropathy known as the Haas system of classification for IgA Nephropathy. Much like lupus nephritis, there is a range of pathologies seen on renal biopsy in patients with IgA Nephropathy, and there is a wide range of prognoses, with many patients going years without any discernable decline in renal function but others which may show a pattern of rapidly progressive glomerulonephritis.
In the Haas paper describing their classification system, the authors took 244 cases of IgA Nephropathy–not including Henoch-Schonlein purpura–and broke down the cases by histologic pattern into 5 subclasses: subclass I (minimal or no mesangial hypercellularity), subclass II (focal and segmental glomerular sclerosis without active cellular proliferation), subclass III (focal proliferative GN), subclass IV (diffuse proliferative GN), and subclass V (any biopsy showing >40% globally sclerotic glomeruli or >40% cortical tubular atrophy or loss). The classification is useful in the sense that there was a statistically significant correlation between IgA subclass and renal survival (with subclass I having the best prognosis and subclass V having the worst prognosis).