How ANCAs be helpful in differentiating vasculitis?
The c-ANCA directed against serine proteinase 3 is highly specific for GPA with widespread systemic involvement (>90%). Less specific is p-ANCA with antimyeloperoxidase specificity, which may be found in MPA and EGPA (Churg–Strauss vasculitis).
If the p-ANCA is not against myeloperoxidase, inflammatory diseases other than vasculitis should be considered (inflammatory bowel disease, infections).
In some patients, ANCAs may have predictive value for relapses and ongoing disease activity.
ANCAs may be pathogenic as part of several simultaneous or sequential events.