The p-ANCA (perinuclear anti-neutrophil cytoplasmic antibody) test, more specifically known as MPO-ANCA, is a type of blood test used to detect autoantibodies against the enzyme myeloperoxidase (MPO) in neutrophils. This test is primarily used for the diagnosis and monitoring of systemic vasculitis conditions such as microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss syndrome), and in some cases of glomerulonephritis.
In the indirect immunofluorescence (IIF) method, the p-ANCA pattern appears as a perinuclear ring-like fluorescence around the neutrophil nuclei. However, to confirm its specificity, the ELISA (enzyme-linked immunosorbent assay) method is used to detect anti-MPO antibodies.
A positive result, particularly when accompanied by symptoms such as small-vessel vasculitis or kidney and lung involvement, may indicate active disease. Nonetheless, p-ANCA positivity can also occasionally be observed in non-vasculitic conditions such as inflammatory bowel diseases (especially ulcerative colitis), autoimmune hepatitis, or infections.
Interpretation of the results should be carried out in conjunction with clinical evaluation, additional laboratory tests (such as tissue biopsy), and imaging studies. While MPO-ANCA plays an important role in early diagnosis, monitoring treatment response, and predicting disease relapse, it is not sufficient on its own for a definitive diagnosis.
