Blood test predicts Alzheimer’s risk up to a decade early

A single blood test measuring levels of the biomarker p-tau217 can reliably predict which cognitively healthy older adults will develop Alzheimer's-related cognitive impairment years before symptoms appear, according to a large-scale study published July 14 in JAMA and presented at the Alzheimer's Association International Conference (AAIC) 2026 in London.allsci+2

Largest Longitudinal Study of Its Kind

The study, led by researchers at Mass General Brigham, pooled longitudinal data from 2,684 cognitively unimpaired older adults across six North American cohorts with follow-up periods extending up to 13.5 years. Participants were stratified into four risk groups based on their baseline p-tau217 levels, anchored to amyloid-PET imaging thresholds.allsci

Those in the "very high" category faced an estimated 38% risk of cognitive impairment within five years and a 78% likelihood over ten years. By contrast, individuals in the lowest tier had only a 12% five-year risk. Each one-standard-deviation increase in p-tau217 corresponded to a 38% greater hazard of progression to clinical impairment, an association that held after adjusting for age, sex, APOE ε4 genetic status, and education level.emjreviews+2

The blood test retained independent prognostic value even when amyloid-PET imaging results were included in the predictive models, suggesting it captures biological information beyond what brain scans alone provide.allsci

Implications for Early Detection and Trials

The findings arrive as the field of Alzheimer's diagnostics undergoes rapid transformation. Separate data presented at AAIC 2026 showed that blood-based biomarker tests helped primary care physicians achieve diagnostic accuracy of roughly 93%, nearly matching the 94% achieved by dementia specialists. Eli Lilly ↘ 0.53% also presented data on July 15 showing that p-tau217 assays performed comparably to amyloid PET for identifying Alzheimer's pathology in cognitively unimpaired individuals.aaic.alz+1

The study authors concluded that plasma p-tau217 shows "robust prognostic value over five and ten years in cognitively unimpaired older adults," positioning the test as a practical tool for enrolling at-risk individuals in prevention trials and guiding future treatment decisions. With several blood tests already receiving regulatory clearance in Europe and the United States, the new evidence strengthens the case for integrating p-tau217 screening into routine clinical practice for older adults concerned about their cognitive future.emjreviews