GFAP and Alzheimer disease: Serum NfL and GFAP levels were significantly higher in AD than in PDD (Table 1), and the AUCs in the differential diagnosis of AD from PDD significantly improved to 86.8% (p < 0.0001) (Fig. 4k) and 88.1% (p = 0.0001) (Fig. 4l), respectively, when combined with serum SV2A.