Objectives:Laboratory detection of myositis-specific autoantibodies (MSAs) utilizes ELISA and multianalyte line blot assays (LBA). We sought to evaluate the concordance and reliability of these two commercial assays.
Methods:Serum samples from patients with idiopathic inflammatory myopathies (IIMs) were obtained from seven countries across the Asia-Pacific region. Anti-Jo-1, anti-EJ, anti-PL-7, anti-PL-12, anti-MDA5, anti-Mi-2 and anti-TIF1-γ antibodies were centrally measured with commercial ELISA and LBA kits. The positive percentage agreement (PPA), negative percentage agreement (NPA) and Cohen’s kappa were calculated by comparing the two assays. Sera with discordant results were subjected to ‘gold-standard’ immunoprecipitation (IP) assays.
Results:Serum samples obtained from 485 patients with IIMs, including 180 with DM, 44 with amyopathic DM, seven with JDM, 197 with PM or immune-mediated necrotizing myopathy and 57 with IBM, were subjected to ELISA and LBA. The PPA was the highest for anti-Jo-1 at 0.98, followed by 0.94 for anti-PL-7, 0.93 for anti-EJ, 0.93 for anti-MDA5, 0.89 for anti-TIF1-γ, 0.78 for anti-PL-12 and 0.67 for anti-Mi-2, whereas the NPA was high (ranging from 0.97 to 1 for all MSAs). Kappa values exceeded 0.80 for anti-Jo-1, anti-EJ, anti-MDA5 and anti-TIF1-γ, whereas anti-PL-7, anti-PL-12 and anti-Mi-2 exhibited low values. IP assays using sera with discordant results revealed a high rate of false positives for anti-PL-7 and anti-Mi-2 in LBA.
Conclusion:Discrepancies in the measurement results were observed between commercially available ELISA and LBA, especially for anti-PL7 and anti-Mi-2. ELISA is more accurate than LBA.