GFAP and Alzheimer disease: Instead, GFAP and pTau 181 were analyzed, at a later time, on aliquots of plasma samples of the first visit still available: GFAP was measured in 42 plasma samples (5 SCD, 25 MCI, 12 AD); pTau 181 was measured in 81 plasma samples (25 SCD, 39 MCI, 17 AD).