Usefulness of antineutrophil cytoplasmic autoantibodies in diagnosing and managing systemic vasculitis

Antineutrophil cytoplasmic autoantibodies (ANCAs) are considered important diagnostic tests in the work-up of patients suspected of vasculitis. Here we discuss new developments in the methodology of testing, the pitfalls in using these tests as diagnostic tools, and the value of serial ANCA testing for the follow-up of patients with ANCA-associated vasculitis including treatment decisions.

Both the indirect immunofluorescence (IIF) test and antigen-specific assays should be performed. New methodologies include automated reading in the IIF test and third-generation assays (anchor ELISA and bead-based multiplex assay) for the antigenic-specific assays. ANCA testing should be done in the right clinical context as positive results for PR3-ANCA and MPO-ANCA do occur in other conditions than vasculitis as well. These ANCAs develop in about 10% of patients with infective endocarditis. The occurrence of drug-induced ANCA and ANCA, also directed against elastase, following use of levamisole-adulterated cocaine should be recognized. In the right clinical context, ANCA are highly sensitive and specific for their associated disease. The value of serial ANCA testing for the follow-up of patients with ANCA-associated vasculitis is still under discussion but may be relevant in patients with renal involvement and in patients treated with rituximab.

The techniques for ANCA testing improve further but new tests should be standardized and validated. Their diagnostic value in the right clinical context is undisputed. Their value for the follow-up of patients is still under discussion.