Overview

• MPO-ANCA (Myeloperoxidase-Antineutrophil Cytoplasmic Antibody) detects antibodies directed against the enzyme myeloperoxidase in neutrophils.

• It shows a perinuclear staining pattern (P-ANCA) on immunofluorescence.

• Primarily used to diagnose ANCA-associated vasculitis.

Risk Assessment

Helps in the evaluation of diseases such as:

• Microscopic polyangiitis (MPA)

• Eosinophilic granulomatosis with polyangiitis (EGPA/Churg-Strauss)

• Renal-limited pauci-immune glomerulonephritis

• Autoimmune disorders causing small-vessel vasculitis

Risk assessment indications:

• Unexplained rapidly progressive renal failure

• Pulmonary-renal syndrome

• Peripheral neuropathy

• Skin purpura / vasculitic rash

• Refractory sinusitis or asthma (EGPA suspicion)

Normal Range

• Negative / < 20 IU/mL
  (May vary slightly depending on the laboratory)

Interpretation

• Positive MPO-ANCA (P-ANCA):

  • Suggests ANCA-associated vasculitis, especially MPA and EGPA.

  • Correlates with disease activity, but not always perfectly.

• Negative MPO-ANCA:

  • Does not completely rule out vasculitis.

  • Other antibodies (e.g., PR3-ANCA) may be positive in GPA.

• False positives may occur in:

  • Ulcerative colitis

  • Rheumatoid arthritis

  • Systemic lupus erythematosus

  • Chronic infections

  • Certain drugs (hydralazine, propylthiouracil, minocycline)

Sample Type

• Serum

  • Collected through a routine venous blood sample.