MPO and rheumatoid arthritis: Compared with the typical ANCA group, participants in the a-ANCA group exhibited a higher levels of RBC, HGB, a lower levels of anti-MPO, serum creatinine, a lower chance of hypertension, CKD, AAV (OR: 0.02, 95 % CI: 0.01–0.07, p < 0.001), and SLE (OR: 0.23, 95 % CI: 0.11–0.48, p < 0.001), but a higher association with RA (OR: 2.99, 95 % CI: 1.15–7.83, p = 0.025) and UC (OR: 5.50, 95 % CI: 1.20–25.29, p = 0.028).