Antineutrophil cytoplasmic Ab

Keywords: Antineutrophil cytoplasmic antibody, ANCA

Specimen:

5 mL blood in plain tube.

Method:

Indirect IF for detection of reaction pattern (c-ANCA, p-ANCA and atypical). Immunoassay to determine specificity (antiproteinase 3, antimyeloperoxidase).

Reference Interval:

Method dependent.

Application:

Assessment of patients with suspected systemic necrotizing vasculitis with and without renal disease – microscopic polyangiitis, idiopathic necrotizing and crescentic glomerulonephritis.

Interpretation:

Cytoplasmic staining (c-ANCA) is frequently associated with antiproteinase 3 antibody and in an appropriate clinical context consistent with renal vasculitis, is a sensitive and specific test for Wegener's granulomatosis. Classical perinuclear staining (p-ANCA)is associated with antimyeloperoxidase antibody and microscopic polyangiitis. Atypical patterns occur in a range of diseases including inflammatory bowel disease and other autoimmune diseases. Antinuclear antibody interferes with determination of pattern.

Positive immunoassays especially at higher titre in general correlate with the presence of systemic necrotizing vasculitis.

In a suggestive clinical context, ANCA positivity should be used to select those patients requiring more intensive investigation, including renal biopsy, to exclude systemic necrotizing vasculitis. Atypical ANCA is associated with a variety of diseases other than vasculitis. A negative ANCA result does not exclude the diagnosis of systemic necrotizing vasculitis.

Reference:

Savage CO et al. BMJ 2000; 320: 1325-1328.