MAPT and Alzheimer disease: Among plasma biomarkers, tau phosphorylated at different epitopes has been shown to hold promise as biomarkers of AD pathologies, with plasma tau phosphorylated at threonine 217 (pTau217) showing the best performance to date.2, 3, 4, 5, 6 This performance varies by assay and capture and detection antibodies used, with best correlation reported to date to Aβ PET of r = 0.74,7 and tau PET of r = 0.78.8