As some of the NMOSD patients with AQP4-Ab may not meet the definite diagnostic criteria for NMO [23], nor does not have clinical features of NMO (high risk group) [24] in their early disease stages, we have measured the sensitivity and specificities of assays in differentiating sera of definite NMO (highly AQP4-Ab positive) from those of controls without IDD or MS (both of these groups should not have AQP4-Ab). Here, AQP4 is linked to neuromyelitis optica.