Clear-positive cut off determination of flow cytometric MOG-antibody assay in Korea: Alignment with international MOGAD diagnostic standards

Abstract

Background: MOG-Ab assay is a sensitive and specific biomarker that is indispensable in diagnosis of MOG antibody-associated disease (MOGAD). However, its accuracy can largely depend on a proper selection of patients also on cut-off value setting. We updated the cut-off value of flow cytometric MOG antibody assay in Korea, into low- and clear-positive, in alignment with 2023 International MOGAD Panel proposal. Methods: We retrospectively analyzed 695 patients who underwent live cell-based flow cytometric MOG-Ab testing at Seoul National University Hospital from August 2023 to January 2024. Cut-off values for mean fluorescence intensity ratio (MFIr) were determined using disease controls, and diagnostic accuracy was assessed at three thresholds: Low Positive (>2.61), Clear-Positive (>5.66), and High Clear-Positive (>10.0). Results: Among 671 non-MS/NMOSD patients, 159 had core clinical demyelinating events, and 66 met 2023 international panel criteria for MOGAD. The diagnostic accuracies for low-positive, clear-positive, and high clear-positive results were as follows: sensitivity of 100 %, 59.1 %, and 33.3 %, respectively; specificity of 95.7 %, 95.9 %, and 100 %; positive predictive value (PPV) of 71.0 %, 90.7 %, and 100 %; and negative predictive value of 100 %, 95.9 %, and 93.5 %. In 159 patients with core clinical demyelinating events excluding MS and NMOSD, clear-positive threshold demonstrated a PPV of 100 %. Conclusion: This study updates the cut-off values of flow cytometric MOG-Ab assay and its diagnostic accuracies in Korea in accordance with the 2023 International Panel recommendation. Our findings can contribute to improving the diagnostic accuracy of MOGAD in Korea and to strengthening the scientific validity of MOGAD research data from Korean cohort.