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To determine the frequency of detection and the age and sex associations of autoimmune/paraneoplastic encephalitis antibody biomarkers (AE-Abs).There were 42,032 patients tested in the Mayo Clinic Neuroimmunology Laboratory between January 2018 and December 2019 for AE-Abs in serum or cerebrospinal fluid (CSF), including NMDA-R-IgG, AMPA-R-IgG, GABAAdult serum analysis (22,472 patients; 56% female) revealed that 814 (3.6%) were positive: NMDA-R-IgG (24.6%)GAD65-IgG (21.5%)LGI1-IgG (20.5%)others. Of children (5649; 50% female), 251 (4.4%) were positive: NMDA-R-IgG (53.1%)MOG-IgG1 (32%)GAD65-IgG (7.1%)others. Adult CSF analysis (18,745 patients; 54% female) revealed that 796 (4.2%) were positive: NMDA-R-IgG (39.7%)GAD65-IgG (28.5%)LGI1-IgG (11.4%)others. Of children (5136; 50% female), 282 (5.5%) were positive: NMDA-R-IgG (88.1%)GAD65-IgG (8.7%)others. Age younger than 20 years was associated with NMDA-R-IgG and MOG-IgG1 (odds ratio [OR], 8.11 and 7.84, respectively; P.001). Age older than 65 years was associated with GABAThe most frequent AE-Abs detected were NMDA-R-IgG, GAD65-IgG, LGI1-IgG, and MOG-IgG1. Age and sex associations may suggest paraneoplastic, or aging influences on neurologic autoimmunity.

To verify the analytical performance of a new mass spectrometry-based method, termed MASS-FIX, when screening for plasma cell disorders in a routine clinical laboratory.Results from 19,523 unique patients tested for an M-protein between July 24, 2018, and March 6, 2020, by a combination serum protein electrophoresis (SPEP) and MASS-FIX were examined for consistency with pretest implementation performance. MASS-FIX's ability to verify abnormal results from SPEP and free light chain measurements was then compared with that of immunofixation electrophoresis (IFE) using a separate cohort of 52,586 patients tested by SPEP/IFE during the same period.Overall, 62.4% of our cohort was negative for an M-protein. Importantly, 7.3% of all specimens had an M spike on SPEP (0.1 to 8.5 g/dL) and MASS-FIX detected an M-protein in all these samples. Of all samples, 30.3% had M-proteins that were detected by MASS-FIX but the SPEP finding was too small for quantification. Of the positive samples, 5.7% contained a therapeutic monoclonal antibody. Of the positive samples, 4.1% had an N-glycosylated light chain (biomarker of high-risk plasma cell disorders). MASS-FIX confirmed a higher percentage of SPEP abnormalities than IFE. MASS-FIX was slightly more sensitive than IFE when confirming an M-protein in samples with an abnormal free light chain ratio. MASS-FIX had a very low sample repeat rate (1.5%). MASS-FIX was highly automatable resulting in a higher number of samples/technologist/day than IFE (∼30% more).Overall, MASS-FIX was successful in maintaining validation characteristics. MASS-FIX was more sensitive in confirming SPEP abnormalities when compared with IFE. Ability to detect therapeutic monoclonal antibodies and glycosylated light chains was distinctly advantageous.