GFAP and Alzheimer disease: Compared with individuals with clinical dementia who had AD biomarker-positive status (either by P-tau181 or P-tau181/Aβ42), those with dementia and biomarker-negative status were of similar age and sex, had lower education levels, and had lower levels of neurodegenerative markers GFAP and NfL (P-tau181 only) (Tables 3 and 4).