Overview

• PR3-ANCA (Proteinase-3 Antineutrophil Cytoplasmic Antibody) is an autoantibody test used primarily to diagnose Granulomatosis with Polyangiitis (GPA) and other ANCA-associated vasculitides.

• C-ANCA pattern on immunofluorescence typically correlates with PR3 antibodies.

Risk Assessment / Clinical Use

• Helps assess risk of:

  • ANCA-associated small vessel vasculitis

  • Granulomatosis with Polyangiitis (GPA)

  • Disease activity or relapse in established cases

• Elevated PR3-ANCA increases clinical suspicion of autoimmune vasculitis, especially with symptoms like sinus disease, pulmonary infiltrates, hematuria, neuropathy, or skin lesions.

Normal Range

• Negative: < 20 U/mL (may vary by lab)

• Borderline: 20–25 U/mL (lab dependent)

• Positive: > 25 U/mL

(Some labs use qualitative terms: Negative / Equivocal / Positive.)

Interpretation

• Positive PR3-ANCA:

  • Strongly suggests GPA (high specificity).

  • Also seen in microscopic polyangiitis (less common).

  • Level often correlates with disease activity, but not always.

• Negative PR3-ANCA:

  • Does not completely rule out vasculitis.

  • GPA may still occur with MPO-ANCA or be ANCA-negative.

• Low-titer positivity:

  • May occur in infections, inflammatory diseases, or certain drugs.

  • Clinical correlation is essential.

Sample Type

• Serum (preferred)

• 3–5 mL blood collected in a plain / SST tube