B-112 Routine Application of PR3- and MPO-ANCA Chemiluminescence Immunoassays Demonstrates Enhanced Detection Rates

Abstract

Abstract Background Sensitive and accurate PR3- and MPO-ANCA detection are crucial in the diagnosis and monitoring of patients with ANCA-associated vasculitides (AAV) and the specific diseases categorised thereof, including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA). Chemiluminescence immunoassays (ChLIA) and bead technology have emerged as promising tools for fast, sensitive and accurate autoantibody detection. Applied to PR3- and MPO-ANCA, they could improve limitations in sensitivity, narrow measuring range and level of quantification seen in other assay formats. Here, we examined the routine performance of ChLIAs using human native MPO as well as human recombinant PR3 antigens. Methods The Anti-PR3 ChLIA (IgG) and prototype Anti-Myeloperoxidase ChLIA (IgG) were processed on the RA Analyzer 10 (EUROIMMUN) and the EliA PR3S and EliA MPOS on the Phadia250 (Thermo-Fisher Scientific), both in accordance to the recommendations by the manufacturers. For a comparative analysis of the routine performance, 675 sera from 615 individuals requested for PR3-ANCA, MPO-ANCA or both at the Central Diagnostic Laboratory at Maastricht University Medical Center were measured with the respective assays from both automation systems. The results were compared in respect to the qualitative outcome and numerical correlation. Results Of the total 675 samples, 585 and 556 were subjected to PR3-ANCA and MPO-ANCA analysis, respectively. For both ANCA types, all samples found positive with EliAs were also positive in the corresponding ChLIAs. 24 and 26 samples resulted positive for PR3- and MPO-ANCA by ChLIA, respectively, but were below cut-off in the relevant EliA test. Of those, 50.0% (n = 12 for PR3) and 96.2% (n = 25 for MPO) were from individuals in follow-up after AAV diagnosis, in the remaining cases an ANCA involvement was suspected based on symptoms of the patients. The overall concordance between the two assay systems was 96.0% for PR3-ANCA and 95.4% for MPO-ANCA detection. Conclusion In a routine scenario, the ChLIAs fully covered the PR3- and MPO-ANCA detection by the compared reference test system. Moreover, further positive results in samples found negative by EliA demonstrated enhanced detection rates by both ChLIAs, predominantly in samples from individuals with a known history of AAV. The clinical relevance will be subject to further studies.