AQP-4 (Aquaporin-4 antibody)
This test is done to detect antibodies against aquaporin-4, a water channel protein found in the central nervous system. These antibodies are strongly associated with neuromyelitis optica spectrum disorder (NMOSD), an autoimmune condition that causes inflammation of the optic nerves and spinal cord. It helps differentiate NMOSD from multiple sclerosis and guides diagnosis and treatment.