A blood test for phosphorylated tau 217 (p-tau217) recently received federal clearance, yet questions have persisted about its ability to predict cognitive impairment in cognitively healthy people. An international study led by researchers at the Mass General Brigham Neuroscience Institute examined the test’s prognostic value across six cohorts spanning North America, Japan, and Australia, involving 2,684 cognitively unimpaired older adults.

The investigation found that cognitively unimpaired individuals with very high p-tau217 levels faced a 38% absolute risk of developing cognitive impairment over five years, with risk reaching 78% over ten years, though the longer-term estimates were based on more limited data. The blood test predicted risk independently of amyloid-beta plaques and genetic factors such as APOE4. Roughly 478 of the study participants progressed to cognitive impairment during follow-up assessments that began as early as 2004.

“We do not yet have disease-modifying treatments for people at high risk for cognitive impairment. Our medical advice remains: exercise regularly, maintain a healthy diet, and prioritize sleep.”

Reisa Sperling, MD, senior author

Lead author Rachel F. Buckley, PhD, said what sets the work apart is its ability to estimate an individual’s risk level for cognitive impairment, rather than simply flagging elevated biomarkers. The researchers cautioned that the study’s design, while having strengths, remains limited by selection bias and focuses on relatively short-term rather than lifetime risks.

“Today, p-tau217 can help identify people at high risk for participation in prevention trials,” Sperling explained.

Publication

The study, “Prognostic Value of Blood-Based P-Tau217 Levels for Progression to Cognitive Impairment,” was published in JAMA (DOI: 10.1001/jama.2026.12556). It was supported by the National Institutes of Health, the U.S. Department of Defense, Eli Lilly, the Alzheimer’s Association, the Accelerating Medicines Partnership, the GHR Foundation, and private donors.