A point-of-care diagnostic test for aquaporin-4 antibody seropositive neuromyelitis optica

Abstract

BackgroundGiven the need for specialized laboratory techniques, diagnostic testing for serum antibodies to aquaporin-4, a protein associated with neuromyelitis optica spectrum disorder (NMOSD), is not globally accessible. We aimed to evaluate a novel point-of-care, filter paper-based test for serum AQP4 antibodies (AQP4-Ab). MethodsAdults with AQP4-Ab seropositive NMOSD and seronegative controls (with other central nervous system demyelinating diagnoses) used lancets to place blood drops (∼1 mL) on filter paper cards. Samples were analyzed after an average of 9.4 days using transfected AQP4-GFP HEK293 cells, and results were compared to participants’ prior serum AQP4-Ab test results by blinded laboratory staff. ResultsOf 40 participants (mean age 53.7 years; 83% female), 25 were cases and 15 were controls. The most common diagnosis of controls was multiple sclerosis (73%). The average NMOSD disease duration was 6.3 years. All AQP4-Ab seropositive participants were on disease modifying therapies at the time of participation. The point-of-care test yielded a sensitivity of 80% and specificity of 93% (positive and negative predictive values 95% and 74%). ConclusionThis point-of-care AQP4-Ab testing method may become a pragmatic option to diagnose AQP4-Ab seropositive NMOSD in difficult-to-reach settings. This method should be confirmed with other testing parameters and field tested in new populations.