Israel Medical Association Journal

Anti-neutrophil cytoplasm antibodies are important markers of certain small vessel necrotizing vasculitides, but the optimal use of laboratory results in daily clinical practice necessitates collaboration between clinicians and laboratory specialists. Physicians must familiarize themselves with ANCA tests in ANCA-related vasculitides as well as in differential diagnostic patient populations in order to define cutoff values. Indirect immunofluorescence with a consensus-agreed technique combined with standardized enzyme immunoassays is the modality for detecting the main SSV-associated ANCA specificities using cutoff values that can sufficiently distinguish SVV from non-SVV patients. The combined use of IF and direct EIA to demonstrate proteinase 3-ANCA and myeloper­oxidase-ANCA at significant levels leads to a very high diagnostic specificity towards SVV conditions such as Wegen­er’s granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome, and limited forms of these such as renal-limited focal necrotizing glomerulonephritis. A strong reactivity of ANCA against several azurophil granule components indicates a drug-induced syndrome. ANCA-related SVV and drug­induced vasculitis or lupus syndromes have characteristic ANCA profiles that can help distinguish these conditions from other inflammatory diseases.

Objectives: To help clinicians and laboratory scientists recognize and utilize vasculitis-related ANCAs as an aid in diagnostic workup and patient follow-up, and be aware that ANCAs with different characteristics are commonly found in other chronic inflammatory conditions that persistently engage neutrophils in the inflammatory process.

Methods: Indirect immunofluorescence and enzyme immunoassay methods were used to detect ANCAs with both known and unknown neutrophil autoantigenic targets.

Results: Primary necrotizing small vessel vasculitides such as Wegener’s granulomatosis, Churg-Strauss syndrome, microscopic polyangiitis, and renal-limited rapidly progressive necrotizing glomerulonephritis target either the serine protease proteinase 3 or myeloperoxidase  in azurophilic granules. In ulcerative colitis and rheumatoid arthritis, we found multiple ANCA targets contained in azurophilic and specific granules, the cytosol and the nucleus, whereas PR3² and MPO³ were not, or only weakly, recognized.

Conclusions: ANCAs typically found in active SVV⁴ are demonstrable both by indirect immunofluorescence and antigen-specific enzyme immunoassay, and strong reactivity to either PR3 or MPO is characteristic. Strong ANCA with MPO reactivity is also found in some patients with drug-induced syndromes (lupus, vasculitis). Intermediate to strong perinuclear ANCAs are found in a substantial proportion of patients with UC⁵ (40–60%) and RA⁶ (30–70%), but in these conditions the ANCAs have many antigen targets that are only weakly recognized.

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¹ ANCA = anti-neutrophil cytoplasm antibody

² PR3 = protease proteinase 3

³ MPO = myeloperoxidase

⁴ SVV = small vessel vasculitides

⁵ UC = ulcerative colitis

⁶ RA = rheumatoid arthritis