Evaluation of automated multi-parametric indirect immunofluorescence assays to detect anti-neutrophil cytoplasmic antibodies (ANCA) in granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA)

Objectives: The aim of this multicenter EUVAS study was to evaluate the diagnostic performance of multi parametric indirect immunofluorescence (IlF) assays to detect anti-neutrophil cytoplasmic antibodies (ANCA) in granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). Patients and methods: The study included 912 samples from diseased controls and 249 diagnostic samples from GPA (n = 183) and MPA (n = 66) patients. The performance of two automated multi-parametric assays [Aklides (Medipan/Generic Assays) and EuroPattern (Euroimmun)] combining IIF on cellular and purified antigen substrates was compared with two manual IIF analyses and with commercially available ELISAs for MPO- and PR3-ANCA (Euroimmun). Results: The area under the curve (AUC) of the receiver operating characteristics (ROC) curve to discriminate AAV from controls was 0,925, 0.848, 0.855 and 0.904 for, respectively, the two manual analyses, Aklides and EuroPattern, and 0.959, 0.921 and 0.886 for, respectively, antigen-specific ELISA, antigen-coated beads, and microdot, respectively. Variation in pattern assignment between IIF methods was observed. Conclusion: The performance of IIF depends on the substrate used and the definition of IIF patterns. The performance of automated IIF is improved by multi-parameter testing (combined IIF and antigen-specific testing). Given the variability between IIF methods, the diagnostic importance of this technique is questioned.