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Introduction: As recognition of myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease becomes more widespread, the importance of appropriately ordering and interpreting diagnostic testing for this antibody increases. Several assays are commercially available for MOG testing, and based on a few small studies with very few discrepant results, some have suggested that live cell-based assays (CBA) are superior to fixed CBA for clinical MOG antibody testing. We aimed to determine the real-world agreement between a fixed and live CBA for MOG using two of the most commonly available commercial testing platforms. Methods: We compared paired clinical samples tested at two national clinical reference laboratories and determined the real-world agreement between the fixed CBA and live CBA. Results: Of 322 paired samples tested on both platforms, 53 were positive and 246 were negative by both methodologies (agreement 92.9%, Cohen's kappa 0.78, [0.69-0.86]). Spearman correlation coefficient was 0.80 (p < 0.0001). Of the discrepant results, only 1 of 14 results positive by the live CBA had a titer greater than 1:100, and only 1 of 9 results positive by the fixed CBA had a titer of greater than 1:80. Lower titers on the fixed CBA correlate to higher titers on the live CBA. Conclusion: Overall, there is excellent agreement between fixed and live CBA for MOG antibody testing in a real-world clinical laboratory setting. Clinicians should be aware of which method they use to assess any given patient, as titers are comparable, but not identical between the assays. [ABSTRACT FROM AUTHOR]