To assess the sensitivity, specificity, and stability of AQP4-IgG detection in DBS. 

NMOSD is a devastating inflammatory CNS disease that results in blindness and paraplegia if left undiagnosed and untreated. It is most frequent in Asian and African populations. Access to testing and treatment is extremely limited in developing nations. Blood collected and dried on a paper card (dried blood spot [DBS]) offers a cost-effective simple method for collecting, preserving, and transporting blood specimens in settings with minimal infrastructure. 

Patients with known AQP4-IgG seropositivity used lancets to draw blood from their index fingers and placed approximately 1mL on Whatman® 903 Protein Saver Cards that were either collected in clinic or mailed in the Mayo Clinic Neuroimmunology Laboratory for AQP4-IgG testing on a live-cell cell-binding assay using HEK293 cells transfected with AQP4-expressing plasmid and tested by flow cytometry (gold standard for AQP4-IgG detection). A 13 mm punch, corresponding to 80 uL of blood from the DBS, was soaked in 200 uL of LCBB overnight to extract the antibodies from the paper and were then tested for AQP4-IgG detection. Disease Control samples were also tested.

30 AQP4-IgG+ NMOSD patients provided DBS. Fifteen had DBS and serum collected at the same time, 13 (87%) of the DBS tested positive. The remaining 15 patients sent the DBS by mail: 13 (87%) of the DBS tested positive (no concurrent serum sample, previously tested positive). DBS at room temperature analyzed at 3 (n=5) and 9 months (n=4) demonstrated AQP4-IgG positive results in all cases. All DBS from 50 disease control (including MOG-IgG positive samples) were negative.

DBS has a sensitivity of 87% compared with serum for AQP4-IgG detection. The positive signal persisted despite storage at room temperature for up to 9 months.  DBS collection holds promise to improve access to AQP4-IgG testing and NMOSD diagnosis worldwide.