Anti-neutrophil cytoplasmic antibody (ANCA) levels directed against proteinase-3 and myeloperoxidase are helpful in predicting disease relapse in ANCA-associated small-vessel vasculitis.

Since the discovery of the link between anti-neutrophil cytoplasmic antibodies (ANCA) directed against proteinase-3 (PR3) and myeloperoxidase (MPO) and small-vessel vasculitis, the diagnostic potential of these antibodies has been appreciated [1,2]. High sensitivity and specificity of validated antigen-specific tests for Wegener’s granulomatosis (WG), microscopic polyangiitis (MPA) and the renal limited form of small-vessel vasculitis, pauci-immune necrotizing glomerulonephritis (renal limited vasculitis; RLV), have been demonstrated [3]. It should be stressed that it is essential to use antigen-specific tests such as ELISA with purified antigen in addition to the screening by indirect immunofluorescence (IIF) on ethanol-fixed neutrophils as the finding of a diffuse cytoplasmic (C-ANCA) or perinuclear fluorescence pattern (P-ANCA) is not equivalent to the presence of antibodies directed against PR3 and MPO, respectively (Table 1). Especially the finding of P-ANCA lacks specificity as these can be found in many other conditions. The finding that ANCA levels fall or become negative once disease remission has been obtained and in vitro data suggesting a pathophysiological role for these antibodies have fuelled the thought that, in addition to their diagnostic value, ANCA are more directly related to disease activity of the vasculitic process [4].