GFAP and Alzheimer disease: Astrocytes are part of the neurovascular unit and the blood-brain barrier, which is altered in individuals with AD.51 Astrocytic end-feet cover brain capillaries, which may be a direct route for the release of GFAP from reactive astrocytes to the bloodstream.52 It could be speculated that blood-brain barrier dysfunction facilitates the release of GFAP into the bloodstream; this may also explain the elevations of plasma GFAP in individuals with acute neurologic injuries.