Anti-neutrophil cytoplasmic antibodies are a complex group of autoantibodies (over 40 antigens) detected by indirect immunofluorescence using ethanol fixed neutrophils. They are found in a wide range of autoimmune and infectious disease. Three patterns of staining of neutrophils are recognised. c (cytoplasmic)-ANCA: p (peripheral nuclear)-ANCA and a (atypical)-ANCA.A number (>40) of neutrophil autoantigens have been characterised and some have been suggested to have disease associations. However, only two: Proteinase 3 (Pr3) and Myeloperoxidase(MPO) are of significant value diagnostically. Both are associated with small vessel vasculitis. Anti-proteinase 3 antibodies give a c-ANCA pattern and are most commonly associated with Wegener’s granulomatosis; anti-MPO give a p-ANCA pattern and are found in 50% patients with microscopic polyarteritis, pauci-immune glomerulonephritis, but also in some patients with rheumatoid arthritis and SLE.
Anti-Pr3 and anti-MPO are almost mutually exclusive. They exhibit high sensitivity and specificity for a number of vasculitic disorders often now classified as ANCA vasculitis. Levels of these autoantibodies often correlate with disease activity during treatment. Since the majority of ANCA positive sera are however not from patients with vasculitis and the commonest antigens detected by immunofluorescence are not MPO or Pr3, to avoid confusion, we are now routinely only carrying out specific tests for Anti-MPO and Anti-Pr3 antibodies.
Investigation of systemic vasculitis: including glomerulonephritis, Wegeners, MPA, Churg Strauss syndrome, necrotising vasculitis.
Positives ANCA occur in vasculitis and in diseases which may mimic systemic vasculitis e.g. ulcerative cholitis, infective endocarditis, TB, non-Hodgkin’s lymphoma, AIDS Positive ANCA are also found in other diseases where there is significant chronic neutrophil activation e.g cystic fibrosis. pneumonia in the elderly. Positive ANCA samples are assayed for MPO and PR3 which are more specific for vasculitis and whose levels correlate with disease activity.
Indirect immunofluorescence using ethanol fixed human neutrophils.
Test is not routinely carried out. Can be used at descretion of laboratory in unusual cases of ANCA positivity.
Results are positive or negative.
Assay range notes
Sera are titred until staining is removed. Titre range 1:40-1:320.
5 – 7 days
Immunology The James Cook University Hospital