Methodology and quality assurance practices in performing anti-extractable nuclear antigen (ENA) analysis: an EFLM report on an international survey

Objectives Autoantibodies to extractable nuclear antigens (anti-ENA) play a crucial role in the diagnosis of systemic autoimmune rheumatic diseases (SARD). Analytical methods differ in antigen composition and diagnostic performance. We aimed to document the extent of variability amongst laboratories in how anti-ENA testing is conducted, controlled and verified. Methods A survey was developed to collect information on anti-ENA methodology and quality assurance practices. The questionnaire was distributed amongst laboratories by Sciensano (Belgium), national EASI groups (Italy, Croatia, Portugal, Estonia, Greece) and ICAP (worldwide). Results A total of 427 laboratories participated (61 % European, 21 % American, 14 % Asian). More than half (52 %) use two or more anti-ENA methods. Turnaround time varied, but 71 % perform the analysis within 72 h. Urgent testing was offered in 42 % of laboratories. Internal quality control (IQC) was performed in 91 % of laboratories, predominantly with commercial materials. External quality assessment (EQA) participation was also high (87 %), with nearly half participating in more than three distributions annually. Reagent lot evaluation was less widely implemented (36 %). Forty-three percent tried to limit variability by limiting lot changes. Method verification was performed by 81 % of the laboratories, though sample type and numbers, as well as reproducibility replicates varied considerably. Conclusions This survey highlights substantial heterogeneity in anti-ENA laboratory practice. While most laboratories apply IQC and EQA, significant variation remains in test method(s), turnaround times, lot variability evaluation and verification strategies. Development of more comprehensive recommendations on these topics are essential to improve reliability and comparability of results across laboratories.