Myositis-Specific and Myositis-Associated Autoantibodies in Idiopathic Inflammatory Myopathies: An EASI Survey on Current Clinical and Laboratory Practices

(max. 250) Objectives Detection of myositis-specific and myositis associated autoantibodies (MSA/MAA) aids in classification, diagnosis, and risk stratification of idiopathic inflammatory myopathies (IIM). To identify opportunities for harmonization, we assessed laboratory and clinical variability in IIM serological testing. Methods The European Autoimmunity Standardisation Initiative (EASI) developed questionnaires targeting laboratory medicine specialists and clinicians addressing test initiation, testing methods and algorithms, reporting and interpretation. This was distributed through two external quality assessment (EQA) providers (UK NEQAS and IfQ Lübeck) to laboratory medicine specialists and subsequently to clinicians involved in IIM diagnostics. Results In total 100 laboratory medicine specialists and 56 clinicians responded. Clinicians prefer to restrict requests for MSA/MAA to clinicians specialized in IIM and 97% of them agree with the indications that ask for MSA/MAA analysis as proposed during the 256 th European NeuroMuscular Center (ENMC) workshop. Analysis was almost exclusively performed by commercially available assays (99%). Most laboratories test the ENMC recommended specificities (≥95%), with exception of HMGCR (22%). Both ISO15189 accreditation coverage (39-68%) and antigen-specific verification rates (33-64%) were suboptimal. Implementation of IQC was poor. Primary screening for MSA/MAA using HEp-2 indirect immunofluorescence was considered inappropriate by the majority of laboratory medicine specialists (59%) and clinicians (69%). Result reporting is most often done (semi-)quantitatively (75%) as also preferred by clinicians (91%). Conclusions Considerable variability exists in MSA/MAA test initiation, testing methods and algorithms, reporting and interpretation. Introducing clinical- and laboratory-specific recommendations may contribute to harmonizing the interpretation of routine diagnostics for IIM.