Controversies in ANCA testing.

Antineutrophil cytoplasmic antibody (ANCA) detection is a well-known tool for diagnosing small-vessel vasculitis. Its diagnostic utility, however, depends on the methodologic accuracy of the test and the appropriate ordering of testing in the right clinical setting. While ANCA testing is of proven value, the utility of serial ANCA testing is not entirely clear. Correlation of ANCA levels with disease activity and predicted relapse remains unconfirmed. The best gauge of the predictive value of serial testing is to perform long-term serial testing for some individual patients in order to establish a relationship between ANCA level and clinical disease manifestation over time. ANCA-antigen specificity can be used to assess prognosis in patients with ANCA-associated vasculitis. Proteinase 3-ANCA is associated with higher mortality, higher relapse rate, and faster renal deterioration compared with myeloperoxidase-ANCA. Overall, ANCA is an important diagnostic and prognostic marker for small-vessel vasculitis and warrants further investigation.