AQP4-IgG Assays Comparison in Laboratory Clinical Serivce (S63.004)

OBJECTIVE: To compare aquaporin-4 IgG assays for neuromyelitis optica spectrum disorder (NMOSD) diagnosis, 2011-2013. BACKGROUND: Comparative performances of aquaporin-4 IgG-specific assays in a high-throughput clinical laboratory are unknown. DESIGN/METHODS: All patients were initially tested by service aquaporin-4-ELISA (antigen, M1-aquaporin-4). Additional testing was by cell-based assay (CBA, M1-aqupaorin-4, indirect immunofluorescence) and in-house-developed fluorescence-activated cell sorting (FACS) assays (M1 and M23 isoforms). Results were referenced to pre-test diagnoses. Patient groups comprehensively tested were: Group 1, 388 consecutive Mayo Clinic patients (January-May 2012); Group 2, 615 consecutive Mayo and non-Mayo patients (September 2012); Group 3, 36 patients physician-reported as NMOSD with negative M1-ELISA (2011-2013); Group 4, 41 patients physician-reported as not NMOSD with positive M1-ELISA (2011-2013). FACS results were compared for cells transfected with M1, M23 or both (1:1) in M23-FACS seropositive patients with and without NMOSDs. RESULTS: For Group 1, M1-FACS assay performance was optimum (area under the curve, 0.64 [p=0.02]). Sensitivities were: M1-FACS, 83%; M23- FACS and M1-CBA, 75%; M1-ELISA, 58% (p<0.05). M23-FACS specificity (95%) was lower than for other assays (M1-CBA and M1-FACS, 100%; M1-ELISA, 99%), p=0.004. For 24 Group 2 patients with NMOSD, positive results were yielded by: M23-FACS, 24; M1-FACS, 23; M1-CBA, 20 and M1-ELISA, 18. For 6 Group 2 patients without NMOSD, positive results were yielded by: M23-FACS only, 2; M1-ELISA only, 2; all 3 of M1-CBA, M23 FACS and M1-FACS, 2. For Group 3 patients (false negative M1-ELISA suspected) positive results were yielded by: M1-FACS, 5; M23-FACS, 3; M1-CBA, 2. For Group 4 (false positive M1-ELISA suspected) just one yielded a positive result by another assay. Non-specific IgG binding in M23-FACS was diminished using M1/ M23 co-transfected cells. CONCLUSIONS: Cell binding assays, particularly M1-FACS, have optimum performance and utility in evaluating potential false positive results. False positives in M23-FACS may be attributable to non-specific IgG binding to aquaporin-4 high order arrays. Study Supported by: National Institutes of Health (R01 NS065829) and the Guthy Jackson Foundation. Disclosure: Dr. Fryer has nothing to disclose. Dr. Lennon stands to receive royalty payments for commercial assays to detect of Aquaporin 4-specific Autoantibody. Dr. Pittock9s institution has received compensation for activities with Alexion Pharmaceuticals, MedImmune, and Chugai Pharma. Dr. Pittock stands to receive royalty payments from the technology entitled Neuromyelitis Optica Autoantibodies as a Marker for Neoplasia. Dr. Pittock has received research support from Alexion Pharmaceuticals, Inc. Dr. Jenkins has nothing to disclose. Dr. Horta has nothing to disclose. Dr. Jedynak has nothing to disclose. Dr. Lucchinetti stands to receive royalty payments from Biogen Idec. Dr. Shuster has received personal compensation for activities with Prime Inc. Dr. Weinshenker has received personal compensation for activities with Novartis, Biogen Idec, and Mitsubishi Pharmaceuticals as consultant on data safety monitoring boards; and with Elan Corporation, Ono Pharmaceutical, GlaxoSmithKline Inc., Alexion and Chugai Pharmaceuticals, and Asahi Kasei Medical Company as a consultant. Dr. Weinshenker has received royalty payments from Mayo Foundation. Dr. Wingerchuk has received research support from Genentech, Inc., Genzyme Corporation, Alexion, and TerumoBCT. Dr. McKeon has nothing to disclose.