AQP4 and neuromyelitis optica: At a cut-off value of 2.1 U/mL, as determined by the ROC curve, anti-AQP4 antibody ELISA had a sensitivity of 83.3% (95% CI 62.6–95.2) in patients with NMO, a specificity of 100% (95% CI 87.1–100), a very high positive pLR of ∞ and a nLR of 0.17 (Table 3).