ANCA

      following clinical indications is strongly recommended:

ANCA, (Anti-neutrophil cytoplasmic antibodies) are valuable laboratory markers used for the diagnosis of well-defined types
of small-vessel vasculitis, including granulomatosis with polyangitis (GPA) and microscopic polyangitis (MPA). Anti-neutrophil
cytoplasmic antibodies (ANCA) are autoantibodies directed against cytoplasmic components of neutrophil granulocytes and
monocytes. Using immunofluorescent (IIF) antibody techniques, two main patterns are recognised: cytoplasmic (c-ANCA)
and perinuclear (p-ANCA) . The main antigen for c-ANCA is proteinase 3 (PR3), a serine proteinase present in primary granules,
and p-ANCA patterns in general are due to antibodies directed against myeloperoxidase (MPO).

Due to the availability of high quality immunoassays for PR3- and MPO-ANCA, new international ANCA testing guidelines were
published in 2017 [i]. PR3- and MPO-ANCA are now recommended as the primary screening method for patients with suspected
ANCA-associated vasculitides, GPA and MPA.

• A positive PR3-ANCA and MPO-ANCA occurs in granulomatosis with polyangitis (GPA), microscopic polyangitis (MPA) and
  eosinophilic granulomatosis with polyangitis (EGPA) but is not diagnostic by itself and the diagnosis should be confirmed
  histologically wherever possible. NSH laboratory forward all positive samples for confirmatory IIF at Labplus.
• A diagnosis of vasculitis cannot be excluded on the basis of negative PR3-ANCA and MPO-ANCA results.
• If both PR3-ANCA and MPO-ANCA are negative and there is still strong suspicion of small-vessel vasculitis then ANCA
  immunofluorescence (or second PR3-ANCA and MPO-ANCA immunoassay) is recommended. Please contact the laboratory to discuss.
• PR3-ANCA and MPO-ANCA can be found in several other conditions:
  • Chronic infection can mimic ANCA associated vasculitis (AAV) and patients with infections can develop positive MPO
    and PR3-ANCA. Before establishing a diagnosis of AAV infections such as bacterial endocarditis, Hepatitis C and Tuberculosis
    should be excluded.
  • Combination ANCA testing with IIF and immunoassays is still recommended for other small vessel vasculitidies such as EGPA
    and drug induced vasculitis.

In gastrointestinal disorders P-ANCA is mainly detected in ulcerative colitis 50-67% but is also seen in 6-15% Crohn s disease therefore the
clinical usefulness of ANCAs in IBD has been questioned. The 2017 European evidence based consensus on the diagnosis and management
of ulcerative colitis does not support the routine use of ANCA detection for diagnosis and therapy decisions in ulcerative colitis [ii].
In inflammatory bowel disease the P-ANCA is not usually MPO therefore the MPO-ANCA and PR3-ANCA tests are unlikely to be clinically useful.
If ANCA tests are requested in the context of gastrointestinal disorders please ensure this is specified on the request form so IIF is performed.