Serum antibody testing may help distinguish some causes, as in the following: Antiglomerular basement membrane antibodies: Goodpasture syndrome Antibodies to double-stranded DNA and reduced serum complement levels: Systemic lupus erythematosus Antineutrophil cytoplasmic antibodies (ANCA) to proteinase-3 (PR3-ANCA or cytoplasmic ANCA [c-ANCA]): Granulomatosis with polyangiitis ACNA to myeloperoxidase (MPO-ANCA, or perinuclear ANCA [p-ANCA]): Microscopic polyangiitis Definitive diagnosis requires lung biopsy with findings of small-vessel vasculitis or renal biopsy with findings of glomerulonephritis with or without antibody deposition.