The MPO-ANCA (Myeloperoxidase-specific Anti-Neutrophil Cytoplasmic Antibody) test detects autoimmune antibodies targeting the myeloperoxidase enzyme in neutrophils. It is primarily used to diagnose and monitor systemic ANCA-associated vasculitides, such as:
Microscopic Polyangiitis (MPA)
Eosinophilic Granulomatosis with Polyangiitis (EGPA, formerly Churg-Strauss)
Some cases of Granulomatosis with Polyangiitis (GPA, formerly Wegener’s).
MPO-ANCA (often associated with the p-ANCA pattern in immunofluorescence testing) serves as an immunological marker predicting organ involvement (e.g., rapidly progressive glomerulonephritis in kidneys, lung, or skin). Positive results may correlate with disease activity or relapse and aid in adjusting immunosuppressive therapies (e.g., corticosteroids or rituximab).
However, MPO-ANCA can occasionally appear in other conditions like lupus, rheumatoid arthritis, or drug reactions (e.g., propylthiouracil). Interpretation must integrate clinical symptoms (e.g., pulmonary hemorrhage, renal failure, neuropathy), imaging, and tissue biopsy. Complementary tests like PR3-ANCA (linked to c-ANCA pattern) are essential to differentiate vasculitis subtypes. Definitive diagnosis requires synthesizing clinical, laboratory, and pathological data.
