Concordance for myositis-specific autoantibody detection between commercial enzyme-linked immunosorbent assays and line blot assays: a multicentre study conducted across the Asia-Pacific region

OBJECTIVES: Laboratory detection of myositis-specific autoantibodies (MSAs) utilises enzyme-linked immunosorbent assays (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 (IIM) were obtained from 7 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 dermatomyositis, 44 with amyopathic dermatomyositis, 7 with juvenile dermatomyositis, 197 with polymyositis or immune-mediated necrotising myopathy, and 57 with inclusion body myositis, 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 0.97-1 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.