Performance evaluation of three assays for the detection of PR3-ANCA in granulomatosis with polyangiitis in daily practice

Background: Anti-neutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3-ANCA) are a serological hallmark of small vessel vasculitis, particularly granulomatosis with polyangiitis (GPA). To increase their sensitivity, some ELISA employ the human native PR3 combined with a recombinant protein. Their specificity in daily practice is still to be defined. Our objective was to compare the performance for GPA diagnosis of three PR3-ANCA assays in daily practice. Patients and methods: Seventy-eight consecutive patients' sera with suggestive IIF were included. All sera were tested with a routine Enzyme Linked Immuno adsorbant Assay (ELISA) employing a mixture of human native and human recombinant (hn + hr) PR3 (EUROIMMUN (TM)) compared to two assays using immobilized purified human PR3 (QUANTA Lite (R) ELISA and QUANTA Flash (R) Chemiluminescence assay (CIA), INOVA Diagnostics). Clinical data including BVAS score were collected retrospectively. Results: Nineteen out of the 78 patients had GPA The hn + hr PR3 ELISA had a good sensitivity (100%) but a lower specificity for the diagnosis of GPA (61.0%) than the assays using the sole native protein (hn ELISA: 81.4%, hn CIA: 69.5%). False positive results mainly consisted of patients with inflammatory bowel disease, who had a specific PR3-ANCA positivity assembly when coupling the assays. The antibody titers by human native PR3 assays, but not hn + hr assay, positively correlated with BVAS score. Conclusion: These results highlight the need of a close collaboration between physicians and immunologists. Combining assays including last generation CIA employing human native antigens should improve the performance of GPA's diagnosis. (C) 2013 Elsevier B.V. All rights reserved.