Table 3. International Society of Nephrology/Renal Pathology Society (ISN/RPS) 2003 classification of lupus nephritis

a Indicate the proportion of glomeruli with active and with sclerotic lesions.
b Indicate the proportion of glomeruli with fibrinoid necrosis and/or cellular crescents.
Indicate and grade (mild, moderate, severe) tubular atrophy, interstitial inflammation and fibrosis, severity of arteriosclerosis or other vascular lesions.
Class IMinimal mesangial lupus nephritis
    Normal glomeruli by light microscopy, but mesangial immune deposits by immunofluorescence
Class IIMesangial proliferative lupus nephritis
    Purely mesangial hypercellularity of any degree or mesangial matrix expansion by light microscopy, with mesangial immune deposits
    May be a few isolated subepithelial or subendothelial deposits visible by immunofluorescence or electron microscopy, but not by light microscopy
Class IIIFocal lupus nephritisa
    Active or inactive focal, segmental or global endo- or extracapillary glomerulonephritis involving <50% of all glomeruli, typically with focal subendothelial immune deposits, with or without mesangial alterations
    Class III (A)Active lesions: focal proliferative lupus nephritis
    Class III (A/C)Active and chronic lesions: focal proliferative and sclerosing lupus nephritis
    Class III (C)Chronic inactive lesions with glomerular scars: focal sclerosing lupus nephritis
Class IVDiffuse lupus nephritisb
    Active or inactive diffuse, segmental or global endo- or extracapillary glomerulonephritis involving ≥50% of all glomeruli, typically with diffuse subendothelial immune deposits, with or without mesangial alterations. This class is divided into diffuse segmental(IV-S) lupus nephritis when ≥50% of the involved glomeruli have segmental lesions, and diffuse global (IV-G) lupus nephritis when ≥50% of the involved glomeruli have global lesions. Segmental is defined as a glomerular lesion that involves less than half of the glomerular tuft. This class includes cases with diffuse wire loop deposits but with little or no glomerular proliferation
    Class IV-S (A)Active lesions: diffuse segmental proliferative lupus nephritis
    Class IV-G (A)Active lesions: diffuse global proliferative lupus nephritis
    Class IV-S (A/C)Active and chronic lesions: diffuse segmental proliferative and sclerosing lupus nephritis
Active and chronic lesions: diffuse global proliferative and sclerosing lupus nephritis
    Class IV-S (C)Chronic inactive lesions with scars: diffuse segmental sclerosing lupus nephritis
    Class IV-G (C)Chronic inactive lesions with scars: diffuse global sclerosing lupus nephritis
Class VMembranous lupus nephritis
    Global or segmental subepithelial immune deposits or their morphologic sequelae by light microscopy and by immunofluorescence or electron microscopy, with or without mesangial alterations
    Class V lupus nephritis may occur in combination with class III or IV in which case both will be diagnosed
    Class V lupus nephritis show advanced sclerosis
Class VIAdvanced sclerosis lupus nephritis
    ≥90% of glomeruli globally sclerosed without residual activity