Anti-neutrophilic cytoplasmic antibodies (ANCA)
Related Subjects: Granulomatosis with Polyangiitis GPA (Wegener's)
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Goodpasture's syndrome (Anti GBM disease)
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Respiratory Failure
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Acute Kidney Injury
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⚠️ A negative ANCA test does not fully exclude vasculitis. Always interpret results in the context of clinical features and biopsy where appropriate.
🔎 About Anti-neutrophil Cytoplasmic Antibodies (ANCA)
- ANCA = a heterogeneous group of autoantibodies directed against cytoplasmic components of neutrophils (over 40 antigens identified).
- They are useful clinical markers of vasculitis, especially small vessel vasculitis.
- ANCA titres often correlate with disease activity but are not perfect predictors of relapse.
- Also found in other inflammatory diseases (e.g. IBD, autoimmune hepatitis, infections).
🧬 Cytoplasmic c-ANCA (PR3)
- Targets proteinase 3 (PR3), a serine protease in neutrophil granules.
- Strongly associated with Granulomatosis with polyangiitis (GPA, formerly Wegener’s) – positive in ~90% of systemic cases.
- Patients with limited GPA (ENT-only disease) are less likely to have positive ANCA.
- Clinical pearl: c-ANCA (PR3) = GPA, think of ENT + lung + kidney involvement 👃🫁🩸.
🧬 Perinuclear p-ANCA (MPO)
- Targets myeloperoxidase (MPO), another neutrophil enzyme.
- Classically seen in:
- Microscopic polyangiitis (MPA) (~70%)
- Eosinophilic granulomatosis with polyangiitis (EGPA) (~40%)
- Ulcerative colitis (70%) and Crohn’s disease (20%)
- Typical clinical associations:
- 💥 Rapidly progressive glomerulonephritis (RPGN)
- 💨 Pulmonary haemorrhage (alveolar capillaritis)
❓ Atypical ANCA
- Seen in autoimmune and inflammatory conditions outside the classic vasculitides (e.g. IBD, primary sclerosing cholangitis, autoimmune hepatitis).
- Patterns are variable and less specific.
🧾 Clinical Relevance
- Always combine ANCA with clinical assessment + biopsy for definitive diagnosis.
- PR3-ANCA → think GPA, relapsing course, ENT + renal involvement.
- MPO-ANCA → think MPA/EGPA, often renal + lung haemorrhage.
- Atypical ANCA → non-vasculitic autoimmune disease (e.g. IBD, PSC).
