MPO and vasculitis: These variables will be related to the following: (i) the patient (past history of diabetes mellitus, hypertension, or nephrotoxic exposure with subsequent kidney fibrosis; age; intrinsic sensitivity or resistance to kidney injury); or (ii) the vasculitis (MPO or proteinase-3 ANCA serotype; intensity and duration of renal vasculitis; and specific kidney response to vasculitis; e.g., thrombotic microangiopathy, granuloma, acute tubular necrosis).