MPO and Nephropathy: As for renal involvement, idiopathic double-positive AAV and MPO-AAV demonstrated more severe kidney damage than PR3-AAV patients, which was reflected by higher initial serum creatinine(Dp-AAV vs. MPO-AAV vs. PR3-AAV) (473.4 (167, 659) μmol/L vs. 329.5 (161.775, 562) μmol/L vs. 104 (64, 215.2) μmol/L) (P < 0.05) and lower initial eGFR (Dp-AAV vs. MPO-AAV vs. PR3-AAV) (7.42 (6.82, 30.78) mL/(min·1.73 m2) vs. 14 (7.3, 32.9025) mL/(min·1.73 m2) vs. 72.81 (35.495, 111.19) mL/(min·1.73 m2)) (P < 0.05).