GFAP and Alzheimer disease: However, changes in plasma NfL, Aβ42/Aβ40, Aβ42, and Aβ40 were less pronounced; (2) plasma biomarkers exhibited smaller dynamic ranges than their CSF counterparts, except for GFAP which was the opposite; (3) plasma GFAP and p-tau181 outperformed other plasma biomarkers in tracking AD neuropathology and increased across age only in Aβ-positive individuals.