Comparison of different ANCA detection methods in a predominantly MPO-ANCA-associated vasculitis cohort

We compared different antineutrophil cytoplasmic antibody (ANCA) detection methods using a predominantly myeloperoxidase (MPO)-ANCA-associated vasculitis cohort. Stored sera from 147 patients with untreated ANCA-associated vasculitis (AAV), including microscopic polyangiitis and granulomatosis with polyangiitis (n = 115 and 32, respectively), and 124 disease controls were tested for P-ANCA and C-ANCA with immunofluorescence (IIF), and for MPO-ANCA and proteinase 3 (PR3)-ANCA with different antigen-specific immunoassays: direct enzyme-linked immunosorbent assay (ELISA), chemiluminescent enzyme immunoassay (CLEIA), third-generation fluorescent enzyme immunoassay (FEIA), and latex turbidimetrical immunoassay (LTIA). In addition, MPO-ANCA and PR3-ANCA titers were calibrated using certified reference materials (CRMs). The sensitivities and specificities for AAV diagnoses were 95% and 94% (IIF), 86% and 98% (ELISA), 93% and 94% (CLEIA), 92% and 96% (FEIA), and 68% and 88% (LTIA). Dual IIF/antigen-specific immunoassay testing reduced diagnostic accuracies from 94% to 93%. The quantitative agreement between ANCA levels measured using CLEIA and FEIA and calibrated using CRMs was not good. In conclusion, this study demonstrated the high performance of antigen-specific immunoassays for AAV diagnosis in a predominantly MPO-ANCA-associated vasculitis cohort and suggested that the benefit of dual IIF/antigen-specific immunoassay testing is limited. Standardizing ANCA measurements using different immunoassays was difficult, even when using CRMs.