In ANCA-associated vasculitis (granulomatosis with polyangiitis), which ANCA pattern and target antigen combination is MOST specific for the diagnosis?

• A c-ANCA / PR3 (proteinase 3) ✓
• B p-ANCA / MPO (myeloperoxidase)
• C p-ANCA / elastase
• D c-ANCA / MPO

Explanation

Granulomatosis with polyangiitis (GPA, formerly Wegener's) is characterised by c-ANCA (cytoplasmic immunofluorescence pattern) with specificity for PR3 (proteinase 3) in approximately 70-80% of cases. Microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis (EGPA/Churg-Strauss) more commonly show p-ANCA/MPO. While c-ANCA/PR3 has >95% specificity for GPA in the right clinical context, ANCA results should always be interpreted alongside clinical and histological findings. PR3-ANCA is associated with more relapses compared to MPO-ANCA.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.