What is a PR3 (Proteinase 3) and What Does it Mean

Anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) is a group of autoimmune diseases characterized by inflammation and damage to small blood vessels.

Your Proteinase 3 antibody is the best test to indicate Granulomatosis with Polyganiitis. Although a small number of GPA patients don't have this marker and are diagnosed via biopsy.