PT - JOURNAL ARTICLE AU - Majed, Masoud AU - Fryer, James P. AU - McKeon, Andrew AU - Lennon, Vanda A. AU - Pittock, Sean J. TI - Clinical utility of testing AQP4-IgG in CSF AID - 10.1212/NXI.0000000000000231 DP - 2016 Jun 01 TA - Neurology - Neuroimmunology Neuroinflammation PG - e231 VI - 3 IP - 3 4099 - http://nn.neurology.org/content/3/3/e231.short 4100 - http://nn.neurology.org/content/3/3/e231.full SO - Neurol Neuroimmunol Neuroinflamm2016 Jun 01; 3 AB - Objective: To define, using assays of optimized sensitivity and specificity, the most informative specimen type for aquaporin-4 immunoglobulin G (AQP4-IgG) detection.Methods: Results were reviewed from longitudinal service testing for AQP4-IgG among specimens submitted to the Mayo Clinic Neuroimmunology Laboratory from 101,065 individual patients. Paired samples of serum/CSF were tested from 616 patients, using M1-AQP4-transfected cell-based assays (both fixed AQP4-CBA Euroimmun kit [commercial CBA] and live in-house flow cytometry [FACS]). Sensitivities were compared for 58 time-matched paired specimens (drawn ≤30 days apart) from patients with neuromyelitis optica (NMO) or high-risk patients.Results: The frequency of CSF submission as sole initial specimen was 1 in 50 in 2007 and 1 in 5 in 2015. In no case among 616 paired specimens was CSF positive and serum negative. In 58 time-matched paired specimens, AQP4-IgG was detected by FACS or by commercial CBA more sensitively in serum than in CSF (respectively, p = 0.06 and p < 0.001). A serum titer >1:100 predicted CSF positivity (p < 0.001). The probability of CSF positivity was greater around attack time (p = 0.03). No control specimen from 128 neurologic patients was positive by either assay.Conclusions: FACS and commercial CBA detection of AQP4-IgG is less sensitive in CSF than in serum. The data suggest that most AQP4-IgG is produced in peripheral lymphoid tissues and that a critical serum/CSF gradient is required for IgG to penetrate the CNS in pathogenic quantity. Serum is the optimal and most cost-effective specimen for AQP4-IgG testing.Classification of evidence: This study provides Class IV evidence that for patients with NMO or NMOSD, CSF is less sensitive than serum for detection of AQP4-IgG.AQP4=aquaporin-4; CBA=cell-based assay; FACS=fluorescence-activated cell sorting; HR-NMO=high risk for neuromyelitis optica; IgG=immunoglobulin G; IRB=Institutional Review Board; MS=multiple sclerosis; NMDAR=NMDA receptor; NMO=neuromyelitis optica; NMOSD=neuromyelitis optica spectrum disorder