Table 1.

Definitions for diagnostic terms according to the 2004 ISN/RPS lupus nephritis classification.

Diffuse	A lesion involving most (≥50%) glomeruli
Focal	A lesion involving <50% of glomeruli
Global	A lesion involving more than half of the glomerular tuft
Segmental	A lesion involving less than half of the glomerular tuft (i.e., at least half of the glomerular tuft is spared)
Mesangial hypercellularity	At least three mesangial cells per mesangial region in a 3-micron thick section
Endocapillary proliferation	Endocapillary hypercellularity due to increased number of mesangial cells, endothelial cells, and infiltrating monocytes, causing narrowing of the glomerular capillary lumina
Extracapillary proliferation or cellular crescent	Extracapillary cell proliferation of more than two cell layers occupying one-fourth or more of the glomerular capsular circumference
Karyorrhexis	Presence of apoptotic, pyknotic, and fragmented nuclei
Necrosis	A lesion characterized by fragmentation of nuclei or disruption of the glomerular basement membrane, often associated with the presence of fibrin-rich material
Hyaline thrombi	Intracapillary eosinophilic material of a homogeneous consistency which by immunofluorescence has been shown to consist of immune deposits
Proportion of involved glomeruli	Intended to indicate the percentage of total glomeruli affected by lupus nephritis, including the glomeruli that are sclerosed due to lupus nephritis but excluding ischemic glomeruli with inadequate perfusion due to vascular pathology separate from lupus nephritis