GFAP and Alzheimer disease: When looking at changes over time for different cognitive groups, plasma GFAP showed a significantly higher longitudinal increase in MCI-AD and Aβ-negative MCI-other compared to Aβ-negative stable MCI (p < 0.0001 both) and Aβ-positive stable MCI (p = 0.049 and p = 0.034, respectively) (Fig. 3b).