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

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.

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.

MSA/MAA positivity was observed with 564/1,127 (50.1%) LIA requests. LIA appropriateness and consistency were 31.6% and 51.3%, respectively. Of the 1,127 LIA requests, 666 (59.1%) included a clinical diagnosis. The appropriateness and consistency of the 666 LIA reports were 53.4% and 86.8%, respectively. Among the 666 patients, 337 (50.6%) were diagnosed as having IIM, and 329 (49.4%) were diagnosed as having a non-IIM disease. In patients with IIM, 288/337 (85.4%) received true-positive MSA/MAA LIA results, whereas 105/329 (31.9%) of patients with non-IIM disease received false-positive results (P<0.001). Significant positive odds ratios were observed for anti-Jo-1, anti-MDA5, anti-PM-Scl-75/100, and MSA-associated anti-Ro52 antibodies (P<0.001).

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.