Development and performance evaluation of novel chemiluminescence assays for detection of anti-PR3 and anti-MPO antibodies

Background: The detection of anti-proteinase 3 (PR3) and anti-myeloperoxidase (MPO) autoantibodies represents a serological hallmark in the diagnosis of small vessel vasculitis such as granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). We evaluated novel chemiluminescence assays (CIAs) for PR3- and MPO-ANCA detection and investigated their utility for disease activity monitoring.

Methods: Sera collected from GPA (n=41) and MPA (n=30) patients were tested by QUANTA Lite® PR-3 and MPO ELISAs (INOVA Diagnostics) and by the QUANTA Flash™ PR3 and MPO CIAs (INOVA). Precision and linearity were analyzed following reference guidelines. The recently launched reference sera for PR3-and MPO-ANCA (Centers of Disease Control and prevention, CDC) were used to establish international units for the new assays. Disease activity was determined using the Birmingham Vasculitis Activity Score.

Results: The international standards for PR3-and MPO-ANCA yielded results of 403 CU and 332 CU in the novel CIAs, respectively. The linearity analysis showed linear regression values>0.97 with slopes between 0.96 and 1.04. Total variation obtained from the precision study showed CV% of ≤7.4 for PR3-ANCA and ≤12.8 for MPO-ANCA. Good agreement (Spearman rho ≥ 0.89) was observed between CIA and ELISA. PR3-ANCA determined by CIA, but not by ELISA, was correlated with disease activity. No correlation was found for MPO-ANCA.

Conclusion: The novel PR3- and MPO-ANCA CIAs show good precision, linearity and correlation to ELISA. In addition, PR3-ANCA by CIA show correlation with disease activity.