Towards harmonization of autoantibody detection in relation to paraneoplastic neurological syndromes (PNS): a European Survey on laboratory practices

Objectives: Detection of paraneoplastic anti-neuronal antibodies (PNS autoantibodies) aids in diagnosing the particular syndrome and guides the search for an underlying tumor. To identify opportunities for harmonization that could enhance diagnostic value, we assessed variability in autoimmune serological testing for PNS across laboratories. Methods: The European Autoimmunity Standardisation Initiative (EASI) developed a questionnaire addressing testing methods, digital tools, interpretation, clinical context, and quality assurance. This was distributed through two external quality assessment (EQA) providers (UK NEQAS and IfQ Lübeck) to clinical labs routinely performing PNS autoantibody assays. Results: Among 139 responding laboratories, 78 % perform both cerebellum indirect immunofluorescence (IIF) and line/dot blot assays on serum and cerebrospinal fluid (76 %). Alignment on sample dilution (61 %) and conjugate type (70 %) is variable. Differences in antigen composition and reporting strategies contribute to variability in line/dot blot testing. Digitization is widespread for line/dot blot data (87 %) but limited for cerebellum IIF (31 %). About 53 % use testing algorithms that vary by sample type and requested antibodies. Internal quality control is performed by 89 % (IIF) and 48 % (line/dot blot), mainly using commercial controls. Nearly half (43 %) participate in multiple EQA programs; 46 % (IIF) and 42 % (line/dot blot) have ISO15189 certification, with 20 % planning certification. Positivity rates are low (<6 % in 73 % of labs), indicating low pre-test probability. While only 46 % restrict testing by discipline, most labs access clinical context (84 %) and interact with clinicians (63 %). Conclusions: Considerable variability exists in PNS autoantibody assay execution, reporting, and quality control. Introducing lab-specific recommendations may harmonize practices and improve diagnostic quality.