How and why should we detect ANCA?

Antineutrophil cytoplasmic antibodies (ANCA) have become an established tool for the diagnosis of systemic vasculitis. The major role for ANCA testing is in diagnosing renal insufficiency of unknown origin, where a positive test indicates whether the patient will benefit from immunosuppressive treatment or not. A negative test result almost completely rules out the presence of systemic vasculitis. In this clinical setting the major antigens for ANCA are proteinase 3 and myeloperoxidase, and antibodies to these antigens can best be tested by ELISA. In other clinical settings like inflammatory bowel disease, arthritis and so on, several other ANCA specificities have been described and the IIF test is preferred. However, the clinical value of these somewhat more esoteric specificities is doubtful. New developments in assay techniques and better knowledge of specific epitopes will lead to tools for the improved diagnosis as well as follow up of patients during treatment, as has already been seen with the capture assay for PR3-ANCA.