GFAP and Alzheimer disease: Previous studies showed that plasma and serum GFAP levels are higher in those with symptomatic AD,9,24,25,26,27 results that are in line with those reported for CSF GFAP levels.24,28,29,30,31 However, less is known about plasma GFAP levels among individuals along the whole AD continuum and, particularly, in those with preclinical AD.