Table 1.

ISN/RPS 2003 Classification of Lupus Nephritis [30] and 2018 Revision [31]

Class	Nomenclature	Lesions description according to 2003 ISN/RPS	2018 Revision
Class I	Minimal mesangial LN	Normal appearance of the glomeruli on LM, mesangial IC deposits on IF and fusion or effacement of podocyte on EM.
Class II	Mesangial proliferative LN	Pure mesangial hypercellularity or mesangial matrix expansion with mesangial IC deposits. Absence of subepithelial or subendothelial IC deposits visible on LM.	Mesangial hypercellularity: ≥4 nuclei fully surrounded by matrix in the mesangial area not including the hilar region.
Class III	Focal LN [$<$50% of the glomeruli involved]  A: Active lesionsa  A/C: Active and Chronic lesionsa  C: Chronic lesionsa	Segmental or global extracapillary or endocapillary proliferative lesions [hypercellularity]b or inactive glomerular scars with focal subendothelial IC deposits with or without mesangial alterations. Such lesions involve <50% of the glomeruli.	Crescent: extracapillary hypercellularity which involves 10% or more of the Bowman’s capsule circumference and composed by a mixture of cells and possible presence of fibrin and fibrous matrix.   Cellular crescent. $>$75% cells and fibrin, $<$25% fibrous matrix   Fibrous crescent: $>$75% fibrous matrix, $<$25% cells and fibrin   Fibrocellular crescent: 25–75% cells and fibrin and the remainder fibrous matrix Adhesion: an area of isolated continuity of extracellular matrix material between the tuft and capsule even when the underlying segment does not have overt sclerosis. Fibrinoid necrosis: fibrin associated with glomerular base membrane disruption and/or lysis of the mesangial matrix; this lesion does not require the presence of karyorrhexis.
Class IV	Diffuse LN [$\ge$50% of the glomeruli involved] Diffuse segmental LNc Diffuse global LN  A: Active lesionsa  A/C: Active and Chronic lesionsa  C: Chronic lesionsa	Segmental or global extracapillary or endocapillary proliferative lesions [hypercellularity]b or inactive glomerular scars typically with diffuse subendothelial deposits with or without mesangial alterations. Such lesions involve $\ge$50% of the glomeruli. Segmental lesion: lesion that affect less than half of the glomerular tuft. Global lesion: lesions that affect more than half of the glomerular tuft.
Class V	Membranous LN	Continuous or granular subepithelial IC deposits with or without mesangial alterations and IC deposits
Class VI	Advanced sclerosing LN [$\ge$90% glomeruli involved]	Globally sclerosed glomeruli without residual activity
			Tubulointerstitial lesions: indicate whether interstitial inflammation occurs in presence or absence of interstitial fibrosis.
			Podocytopathy: glomerular changes consistent with minimal change disease, mesangial proliferation or focal segmental glomerulosclerosis on LM and podocyte effacement on EM, with or without mesangial IC deposits. No evidence of IC deposition in peripheral glomerular capillaries or endocapillary proliferation.

^asee Table 2. ^bThe term ‘proliferative’ has been substituted by hypercellularity in the 2018 revision. ^cDifferentiation among diffuse segmental and diffuse global has been eliminated in the 2018 revision. EM: electron microscopy; IC: immune complex; IF: immune fluorescence; LN: lupus nephritis; LM: light microscopy.