Measurement of circulating DNA-MPO complexes revealed their highest level in patients with active stage of GPA (OD: 0.97 ± 0.34), and this was significantly different (P < 0.05) from the patients in remission of GPA (OD: 0.65 ± 0.29) or healthy control (OD: 0.36 ± 0.14; Fig. 5A). This evidence concerns the gene MPO and granulomatosis with polyangiitis.