Table 4.

Definitions of glomerular lesions derived from the Oxford classification of IgA nephropathy^1,64 and patterns of GN derived from the ISN/RPS lupus classification²²

Glomerular lesions
Mesangial hypercellularity	>3 Mesangial cells per mesangial area
Cellular crescent	Extracapillary cell proliferation of more than two cell layers with >50% of the lesion occupied by cells
Fibrocellular crescent	An extracapillary lesion comprising cells and extracellular matrix, with <50% cells and <90% matrix
Fibrous crescent	Extracapillary crescents with >90% matrix
Endocapillary hypercellularity	Hypercellularity caused by an increased no. of cells within glomerular capillary lumina, causing narrowing of the lumina
Fibrinoid necrosis	Disruption of the GBM with fibrin exudation
Sclerosis	Obliteration of the capillary lumen by increased extracellular matrix with or without hyalinosis or foam cells
Patterns of GN
Minimal mesangial GNa	Normal glomeruli by LM but mesangial immune deposits by IF
Mesangial proliferative GNa	Purely mesangial hypercellularity
Active (proliferative) GNa	Any or all of the following glomerular lesions: endocapillary hypercellularity, karyorrhexis, fibrinoid necrosis, rupture of GBMs, cellular or fibrocellular crescents, subendothelial deposits identifiable by LM, and intraluminal immune aggregates
Necrotizing GN	Segmental or global fibrinoid necrosis
Crescentic GN	≥50% Glomeruli with cellular, fibrocellular, or fibrous crescents (with percentage of crescents always noted in the diagnostic line, even when <50%)b
Membranoproliferative GN	Mesangial and/or endocapillary hypercellularity and thickening of capillary walls caused by subendothelial Ig and/or complement factors
Exudative GN	Neutrophils accounting for >50% of glomerular hypercellularity
Sclerosing GNa	Any or all of the following glomerular lesions: glomerular sclerosis, fibrous adhesions, and fibrous crescents

ISN/RPS, International Society of Nephrology/Renal Pathology Society.

^aExcept for the first two patterns, multiple patterns can occur together in a single specimen (derived from the ISN/RPS lupus classification²²).

^bThe term crescentic GN is used when crescents are present in at least 50% of glomeruli, and applies to immune-complex GN/C3 glomerulopathy. This does not apply to ANCA GN and anti-GBM GN, where less than 50% of the glomeruli may be involved by crescents.