Ultrasensitive immunoassays and immunoprecipitation combined with mass spectrometry have made it possible to measure various proteins characteristic for AD pathophysiology from blood, including different soluble Aβ species (27), soluble tau and phosphorylated tau species (28–32), neurodegeneration by plasma neurofilament light chain (NfL) (33), and gliosis by plasma glial fibrillary acidic protein (GFAP) (34–37). Here, GFAP is linked to Alzheimer disease.