GFAP and Alzheimer disease: Additionally, exploratory blood biomarkers indicated potential disease-modifying effects: plasma phosphorylated tau (p-tau_217) levels decreased by about 23% from baseline in the donanemab-treated group (whereas they tend to increase in progressing AD), and levels of glial fibrillary acidic protein (GFAP), an astrocytic injury marker, fell by roughly 12%.