Retrospective study of N-methyl-D-aspartate glutamate receptor IgG testing outcomes at Labplus, Auckland city hospital, New Zealand, 2015 - 2020, in a clinically demand-managed setting

Objectives: To review the outcomes of N-methyl-D-aspartate glutamate receptor (NMDAR) antibody testing conducted at LabPLUS over the period 2015-2020. Methods: A data extract over the period was obtained detailing patient testing. Retrospectively, a proportion of the tested patient cohort had their clinical records accessed to determine their final diagnoses. Results: 654 patients were tested which resulted in the identification of 24 NMDAR antibody positive patients. All positive patients met a case definition for NMDAR encephalitis. A review of 100 NMDAR antibody negative patients did not identify any that supported a case definition for NMDAR encephalitis. The neurologist vetted cohort was predominantly adult (80%) with higher numbers of females. Patients of both genders 75%) in obtaining CSF specimens for testing from within the NRA (local testing) region which was critical, as 30% of patients would have had a delayed diagnosis and most likely treatment if an independent serum specimen had been sent. The laboratory was able to consistently meet the clinically required KPI of same working day reporting turn around times over the six year period for cases of suspected NMDAR encephalitis. Conclusions: Under the framework of neurologist gate keeping and liaison LabPLUS was able to implement and consistently deliver high value clinical results (antibody positive and negative) that allowed rapid treatment intervention when indicated which then translated into the best possible outcomes for patients with NMDAR encephalitis. The success of the mono-specific NMDAR antibody service allowed further neuroimmunology assays to be added to the diagnostic portfolio.