According to the standards of the World Health Organization, IgA nephropathy is classified into five stages pathologically. The first stage is where most glomeruli appear normal under light microscopy, with only minor mesangial proliferation or associated cellular proliferation, generally showing slight changes without damage to the tubules and interstitium;

The second stage indicates mild lesions where over fifty percent of the glomeruli are normal, with only a small portion of the glomeruli showing mesangial cell proliferation, glomerular sclerosis adhesion, and other changes, without the formation of crescents;

The third stage is focal segmental glomerulonephritis, characterized by diffuse proliferation of mesangial cells and widening of the mesangial areas, with the lesions exhibiting focal segmental changes and comparatively mild interstitial lesions.