Recently developed blood test of Alzheimer’s disease (AD) has been recognized as a promising alternative to CSF and PET, as it is noninvasive, cost-effective, and more accessible. Particularly, plasma p-tau217 shows high sensitivity in detecting β-amyloid (Aβ) and tau positivity in early AD. However, the potential value of p-tau217 in revealing Aβ and tau distribution and predicting future development has not been studied.

We investigated the dose-response associations between p-tau217 and regional Aβ and tau measured by PET, as well as the longitudinal prediction of p-tau217 for prospective Aβ and tau accumulation measured by longitudinal PET.

Cross-sectional and longitudinal analyses.

We used data in Anti-Amyloid Treatment in Asymptomatic Alzheimer’s disease (A4) study (N = 333) for primary analyses and Alzheimer’s Disease Neuroimaging Initiative (ADNI) (N = 410) for validation.

Cognitively unimpaired older adults (N = 333) from A4 study and cognitively unimpaired older adults (N = 222), mild cognitive impairment (N = 114), and dementia (N = 74) from ADNI.

Plasma p-tau217 was measured using Lilly (A4) and Fujirebio (ADNI) assays. ^18-FFlorbetapir PET and ^18-FFlortaucipir PET measured regional Aβ and tau.

Plasma p-tau217 was associated with concurrent Aβ in most cortical regions and tau in temporo-parietal cortices. Longitudinally, p-tau217 predicted brain-wide tau accumulation in widespread cortical regions in preclinical AD, but not Aβ change anywhere.

Plasma p-tau217 shows dose-response, brain-wide relationships with concurrent Aβ and future tau development in preclinical AD, suggesting its potential in disease trajectory monitoring and large-scale screening for individuals approaching certain biological stages of AD in clinical trials.