The appropriate use of antineutrophil cytoplasmic antibody (ANCA) testing in rheumatic diseases

The antineutrophil cytoplasmic antibody (ANCA) test is now available in most routine diagnostic immunology laboratories. Improvement, simplification and standardisation of the testing methodology have enabled it to become more reliable and accessible to clinicians. ANCA has strong association with and is most useful in the diagnosis and management of the ANCA-associated vasculitides which include Wegener's granulomatosis, microscopic polyarteritis, Churg-Strauss syndrome and primary pauci-immune necrotising and crescentic glomerulonephritis. It is found in lower frequency in the other vasculitides and collagen vascular diseases, in chronic inflammatory bowel disease and autoimmune liver disease, and in miscellaneous infective and neoplastic disorders. While the gold standard for ANCA testing remains the indirect immunofluorescence (IIF) assay, identification of ANCA-specific antigens such as proteinase 3 and myeloperoxidase has enabled the development of antigen-specific tests. The antigen-specific solid-phase assays have comparable sensitivity with IIF assays and improved specificity in some instances. However, appropriate use of the ANCA test requires full knowledge of its capabilities and limitations, and the results should always be correlated with clinical data. In particular, it is important to understand that it is not only test sensitivity and specificity, but patient selection that contributes to the positive predictive value and clinical relevance of the test result.