Comparative analysis of different commercial ELISA systems for the detection of anti-neutrophil cytoplasm antibodies in ANCA-associated vasculitides

Objective: To assess the diagnostic performance of 11 commercial PR3- and MPO-ANCA ELISA systems (direct, capture and high sensitive [hs] ELISA). Methods: Sera from 90 patients with AAV (GPA, MPA and CSS) and 20 disease controls (SLE; RA) and healthy individuals were tested for the presence of ANCA by IFT and by different ELISAs for the presence of PR3-and MPOANCA, respectively. Furthermore, the binding capacity of the IUIS-CDC reference sera for PR3-/MPO-ANCA in different commercial assays was analysed. Results: Commercial ELISA kits for PR3-ANCA differed moderately in their sensitivity (from 45% to 62.5%). The highest sensitivity for PR3-ANCA was obtained with hs ELISA (kit A) and capture ELISA (kit N). Testing for MPOANCA the highest sensitivity (85%) was obtained with direct ELISA (kit D and I). Specificity was high in all kits. Only three PR3-ANCA commercial kits and three MPO-ANCA kits produced binding at the expected value for the IUISCDC reference sera (100 U/ml). In all of the kits, serial dilutions of the reference sera did not yield linearity. Conclusion: Second (capture) and third (high sensitivity) generation PR3- ANCA ELISA kits are superior to conventional ELISAs. Direct and capture MPO-ANCA ELISAs showed a good overall performance in all kits. Most of the kits have not been standardised to allow their results to be compared.