Main Disease Association
ANCA-associated vasculitis

Category
Antibody

When to Order
* Clinical signs and symptoms of vasculitis, especially small vessel involvement (glomerulonephritis, diffuse alveolar hemorrhage, leucocytoclastic vasculitis)

What It Means If Positive
* Association with granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis
* Also often positive in infammatory bowel disease and primary biliary cirrhosis
* Recommend ordering more specific testing, such as MPO antibodies. PR3 is a type of C-ANCA autoantibody

What It Means If Negative
* Does NOT rule out vasculitides