Plasma p-tau217, p-tau181, and Aβ42 predict amyloid PET positivity in cognitively unimpaired adults

Early detection of Alzheimer's disease (AD) pathology in cognitively unimpaired individuals is critical for preclinical intervention. Plasma biomarkers, especially phosphorylated tau217 (p-tau217), are promising predictors of amyloid-β (Aβ) accumulation.

In this cohort study, we analyzed data from cognitively unimpaired older adults in the A4 and LEARN studies (n = 1,407), comprising 452 participants with Aβ positron emission tomography (PET)-negative status and 955 participants with Aβ PET-positive status. We evaluated the accuracy of plasma biomarkers (p-tau217, p-tau181, Aβ42/40 ratio, and others) in predicting Aβ PET positivity using receiver operating characteristic analysis, comparing covariate-adjusted individual biomarker and biomarker-ratio models with a multivariable combined model integrating plasma biomarkers and covariates. (age, sex, apolipoprotein E [APOE] ε4 genotype).

Plasma p-tau217 showed the strongest individual association with Aβ PET status (area under the curve [AUC], 0.85). A combined model integrating p-tau217, p-tau181, Aβ42, age, sex, and APOE ε4 achieved the highest overall discrimination (AUC, 0.87), although the improvement over the covariate-adjusted p-tau217 model was modest.

Plasma p-tau217 showed the strongest individual performance for predicting Aβ PET positivity in cognitively unimpaired older adults. Adding other plasma biomarkers and clinical covariates provided a modest incremental improvement in classification performance. These findings support blood-based prescreening as a potential enrichment approach, while indicating that confirmatory amyloid assessment remains necessary when definitive Aβ status is required.