ANCA PR3 are autoantibodies directed against proteinase 3, an enzyme in neutrophils. They are characteristically associated with granulomatosis with polyangiitis and other small-vessel vasculitides. Detected by blood testing (typically a c-ANCA pattern), PR3‑ANCA aids diagnosis, guides treatment decisions, and can help monitor disease activity and relapse risk, especially with respiratory or renal involvement.

PR3 stands for proteinase 3, a neutrophil serine protease encoded by the PRTN3 gene. Located in azurophilic granules, it helps degrade pathogens and regulate inflammation. PR3 is the primary antigen targeted by c-ANCA (cytoplasmic anti-neutrophil cytoplasmic antibodies) and is clinically important in diagnosing and monitoring granulomatosis with polyangiitis.

Anti‑MPO and PR3 are two types of ANCA that target different neutrophil enzymes: myeloperoxidase (MPO) and proteinase‑3 (PR3). PR3‑ANCA is more often linked to granulomatosis with polyangiitis (upper airway and lung involvement) and relapsing disease; MPO‑ANCA is common in microscopic polyangiitis and renal‑predominant vasculitis. They help guide diagnosis, prognosis and treatment decisions.

A positive ANCA (antineutrophil cytoplasmic antibody) test means the immune system has produced antibodies targeting neutrophil components. It raises suspicion for ANCA-associated vasculitis (e.g., granulomatosis with polyangiitis, microscopic polyangiitis) but can also occur with infections, other autoimmune diseases, or drug reactions. It is not diagnostic alone—results require clinical correlation, antibody subtyping (PR3/MPO), imaging, and often biopsy.

Proteinase 3 (PR3) is detected primarily by blood tests for anti‑PR3 antineutrophil cytoplasmic antibodies (PR3‑ANCA) using ELISA and immunofluorescence (c‑ANCA pattern). Diagnosis combines compatible clinical features (sinus, lung, kidney), inflammatory markers, imaging (CT chest/sinuses) and urinalysis. Definitive confirmation often requires biopsy showing necrotizing granulomatous inflammation and small‑vessel vasculitis.

P-ANCA (usually MPO-ANCA) is most commonly associated with microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis (Churg–Strauss). It can also be positive in ulcerative colitis, primary sclerosing cholangitis, and some drug-induced or systemic autoimmune conditions. P-ANCA supports but does not definitively diagnose these diseases; clinical correlation and further testing are required.