GFAP and Alzheimer disease: Participants with AD also had roughly 1.3–1.5-fold higher plasma pTau181, tTau, and GFAP concentrations than ONDs (pTau181 and tTau: p < 0.001; GFAP: p < 0.005; Figure 3, Table 4), again with pTau181 showing the largest fold difference between the groups.