Plasma tau and p-tau changes across groups in Aβ SILK validation cohort. (A) Phosphorylation occupancies on T217 in plasma and CSF correlate. Spearman correlations and associated P value are shown. (B and C) As found in the discovery cohort, plasma p-tau-217/T217 ratio and p-tau-217 level distinguish amyloid-negative from amyloid-positive groups regardless of the cognitive status. Amyloid-negative with high CSF p-tau-217 were also separated from other amyloid-negative groups. Separations between groups are calculated using AUROC. (D) Plasma tau level is not a biomarker for amyloid status and AD dementia. (E and F) Plasma p-tau-181/T181 ratio and p-tau-181 level increase in amyloid-positive groups but are less accurate than p-tau-217 measures to detect abnormal tau phosphorylation. (G and H) Receiver operating characteristic curves discriminating amyloid-positive from amyloid participants using CSF and plasma tau measures. Corresponding AUCs are summarized in Table 2. AUC comparison between p-tau-217 and p-tau-181 measures is described in Table S3. (I) Plasma p-tau-217/T217 ratio associates with Aβ42/40 ratio measured in CSF.