Among the 150 AAV patients, 14 patients (6 EGPA, 6 MPA, and 2 GPA), sampled at the time of diagnosis (before and during the first month of treatment), were negative for both MPO and PR3 ANCAs and also for anti-lactoferrin, -BPI, -elastase, and -cathepsin G aAbs. Here, MPO is linked to granulomatosis with polyangiitis.