Interlaboratory variability in laboratory testing and reporting of myositis autoantibodies

Myositis-specific and myositis-associated autoantibodies (MSA/MAA) are important biomarkers used in the diagnosis and assessment of patients with idiopathic inflammatory myopathies. To date, limited guidance exists on how testing should be undertaken or which MSA/MAA to include in a clinically justifiable 'myositis panel'. We aimed to investigate interlaboratory variability in 'myositis autoantibody testing' in terms of panel components, comparability of test results and approaches to reporting with a view to informing future guidelines.

Twenty-four quality-control sera containing MSA/MAA were shared with 15 participating laboratories located in Europe, North America, Australia and Japan. Laboratories evaluated the samples for MSA/MAA using their usual protocols. Raw data, alongside reported test results, were collated.

Participating laboratories made use of a variety of commercial and in-house assays. Most used at least one commercial multiplex assay and each centre tested for between 14 and 33 autoantibody specificities. Near 100% concordance in the reported result was seen for almost half the samples analysed. As expected, negative results were reported where the previously identified autoantibody was not tested for, but also frequently with putative anti-OJ, anti-EJ and anti-TIF1γ samples. Of concern, the results obtained for anti-TIF1γ sera varied between laboratories using the same commercial assay.

We have shown there is considerable variation in how myositis antibody testing is undertaken and the results obtained for key autoantibody specificities, which may impact on clinical decision-making. Dialogue between manufacturers, diagnostic laboratories and clinicians remains crucial and steps towards harmonisation between laboratories is urgently needed.