However, in certain cases, a clinical context very suggestive of the diagnosis, combined with biological and/or radiological abnormalities, can be considered sufficient to retain a diagnosis of vasculitis in the absence of histological evidence, for example, the presence of ANCA anti-PR3 specificity in most GPA (60% of localized forms, 85% of systemic forms); anti-MPO ANCA in 60% of MPA and in a third of the EGPA; or renal, hepatic, or gastrointestinal microaneurysms on the arteriography during the PAN. Here, MPO is linked to vasculitis.