Performance of the Line Blot Immunoassay for Detecting Myositis Autoantibodies in Real-Life Laboratory Settings: An Italian Multicenter Study

Background: Commercial line immunoassays (LIAs) are used to detect myositis-specific and myositis-associated autoantibodies (MSAs/MAAs) in patients with suspected idiopathic inflammatory myopathy (IIM). However, performance consistency with LIAs remains challenging. We evaluated the appropriateness, clinical consistency, and diagnostic performance of MSA/MAA LIA testing in real-life clinical practice. Methods: Between January and December 2024, eight Italian laboratories performed 1,127 MSA/MAA LIA determinations (Euroline Myopathies 16 Ags plus cN-1A). LIA appropriateness was defined as concordance between the clinical information provided and the MSA/MAA request; clinical consistency was defined as agreement between the IIM diagnosis and LIA results; and diagnostic performance was defined as the reliability of LIA in confirming an IIM diagnosis. Results: <0.001). Conclusions: With increasing MSA/MAA requests for suspected IIM, LIA testing can help identify certain antibodies in real-life scenarios. The appropriateness of the request and the clinical information provided mainly influence the LIA diagnostic performance.