Evolution of autoimmune diagnostics over the past 10 years: lessons learned from the UK NEQAS external quality assessment EQA programs

Objectives: External quality assessment (EQA) programs play a pivotal role in harmonizing laboratory practices, offering users a benchmark system to evaluate their own performance and identify areas requiring improvement. The objective of this study was to go through and analyze the UK NEQAS "Immunology, Immunochemistry and Allergy"EQA reports between 2012 and 2021 to assess the overall level of harmonization in autoimmune diagnostics and identify areas requiring improvement for future actions. Methods: The EQA programs reviewed included anti-nuclear (ANA), anti-dsDNA, anti-centromere, anti-extractable nuclear antigen (ENA), anti-phospholipids, anti-neutrophil cytoplasm (ANCA), anti-proteinase 3 (PR3), anti-myeloperoxidase (MPO), anti-glomerular basement membrane (GBM), rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), mitochondrial (AMA), liver-kidney-microsomal (LKM), smooth muscle (ASMA), APCA, and celiac disease antibodies. Results: In the analyzed period, the number in participating laboratories showed an increase for almost all programs. Among solid phase methods, the use of ELISA techniques showed a progressive reduction, while new technologies, such as the fluoroenzymatic immunoassay, chemiluminescence immunoassay, Luminex and immunoblot showed an increased number of users. The number of results complying with the expected negative or positive target slightly increased for almost all antibodies in the last decade. A description of the most frequent causes of mistakes or misinterpretation for each specific test and method is also provided in this study. Conclusions: Although numerous challenges need to be addressed in the area of autoantibody detection to enhance testing quality and attain higher harmonization, the period analyzed revealed that the ever-expanding range of autoantibodies, coupled with the introduction of new tests and methodologies and the advent of automated platforms, has brought about significant changes in autoimmune diagnostics.