P ANCA

Last reviewed 01/2018

• two ANCA patterns were originally identified by indirect immunofluorescence (IIF): the cytoplasmic (C-ANCA) and the perinuclear (P-ANCA) patterns
  • 'classical' P-ANCA pattern is associated with antibodies to myeloperoxidase (MPO), a 140 kDa heterodymeric enzyme also associated with the antimicrobial properties of neutrophils
  • if IIF and ELISA results are combined, the presence of P-ANCA and anti-MPO has 99% specificity for the diagnosis of primary systemic vasculitis, as does the combination of C-ANCA and anti- PR3
  • P-ANCA and anti-MPO are more often seen in microscopic polyangitis (MPA), Churg-Strauss Syndrome (CSS) and idiopathic necrotising glomerulonephritis
    • in the context of vasculitis, C-ANCA in more than 90% of cases is directed against PR3, whereas in 80-90% of cases P-ANCA reacts with MPO
    • although C-ANCA (anti-PR3) is predominately associated with Wegener's Granulomatosis (WG) and P-ANCA (MPO) with MPA and CSS, there is no absolute specificity
      • between 10 and 20% of patients with classical WG demonstrate P-ANCA and anti-MPO and an even larger number of patients with MPA or CSS have C-ANCA and anti-PR3

Notes:

• 10-20% of patients with WG or MPA and 45-50% of CSS have negative ANCA results

Reference:

1. ARC. Topical Reviews - Rheumatic Diseases: Serological Aids to Early Diagnosis. February 2006.