Assessing Commercial Tissue-Based Assays for Autoimmune Neurologic Disorders (I)
Chiara Milano, Pietro Businaro, Claudia Papi, Lionel Arlettaz, Laura Marmolejo, Laura Naranjo, Matteo Gastaldi, Raffaele Iorio, Albert Saiz, Jesús Planagumà, Eduardo Aguilar, Chiara Pizzanelli, Eugenia Martínez‐Hernández, Thaís Armangué, Mar Guasp, Raquel Ruiz‐García, Lídia Sabater, Josep Dalmau, Francesc Graus, Marianna Spatola
Abstract
BACKGROUND AND OBJECTIVES: Current strategies to detect autoantibodies against intracellular neural antigens (IC-Abs) include tissue-based assays (TBAs) alongside line blots or cell-based assays (CBAs). Many clinical laboratories use commercially available TBAs as a screening test, but their diagnostic yield has not been assessed. We determined the performance of 2 commercial TBAs in detecting IC-Abs. METHODS: We analyzed samples from 100 patients with autoimmune or paraneoplastic neurologic syndromes harboring IC-Abs (confirmed by in-house TBAs and line blots or CBAs) and 50 negative controls. IC-Abs samples included serum (10 each for Hu, Yo, Ri, SOX1, CV2, Ma2, Tr, amphiphysin, and GAD65 antibodies) or CSF (10 with GFAP antibodies) samples. Two commercial indirect immunofluorescence (IIF) TBAs (INOVA and EUROIMMUN) were assessed by 2 experienced investigators and 3 less experienced raters, all blinded to antibody status. Discordant results were re-evaluated through interrater discussion and assessed using Cohen's kappa. RESULTS: = 0.34). Less experienced raters showed higher rates of false-positive results (up to 22% with IIF-EUROIMMUN). DISCUSSION: The performance of commercial IIF-TBAs for IC-Abs detection is suboptimal, exhibiting high false-negative rates of 25%-35%. Therefore, commercial TBAs should not be used alone for IC-Abs screening, but alongside more sensitive techniques, such as line blots. Discordant results between 2 techniques should prompt retesting in reference centers with in-house TBAs, particularly when the suspicion of an autoimmune or paraneoplastic syndrome is high.