Among cognitively normal older adults whose blood carried very high levels of phosphorylated tau 217, the estimated chance of developing cognitive impairment was about 38% within five years and about 78% within ten. Those numbers come from a pooled analysis of 2,684 people followed in six studies, published in JAMA and led by researchers at the Mass General Brigham Neuroscience Institute.
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The ten-year figure carries a caveat the authors themselves stress. It rests on far less follow-up data than the five-year estimate, so it is less certain.
The work was presented at the Alzheimer’s Association International Conference in July and surfaced again on October 30 when ScienceDaily republished the Mass General Brigham summary. The paper, “Prognostic Value of Blood-Based P-Tau217 Levels for Progression to Cognitive Impairment,” is indexed under DOI 10.1001/jama.2026.12556. Rachel F. Buckley, a cognitive neuroscientist, is lead author, and neurologist Reisa Sperling is senior author. The cohorts came from North America, Japan and Australia, with enrollment beginning as early as 2004 and the last follow-up in 2025. About 478 participants went on to develop impairment.
Six cohorts, one blood marker and an individual risk estimate
All participants were cognitively unimpaired when they entered, and each had p-tau217 measured in blood along with a baseline PET brain scan. Annual cognitive assessments tracked who slipped. Buckley said the study stands out because it estimates an individual’s level of risk for cognitive impairment, rather than only showing that the marker differs between groups.
The release reports that p-tau217 stayed significantly associated with later impairment after accounting for amyloid plaques seen on PET, and that its predictive value extended beyond the APOE4 gene variant. In the Mass General Brigham press release, the team describes the test as capturing risk that the scan and the genotype leave out.
Maria C. Carrillo of the Alzheimer’s Association said, in the conference materials, that identifying people at risk earlier could fundamentally change how dementia is diagnosed, treated and prevented. Buckley said that once verified, the blood tests could be used to recruit patients for clinical trials of treatments meant to prevent the disease. The conference release also cautions that p-tau217 alone cannot fully predict individual risk and that age, genetics, kidney function, obesity and race and ethnicity can affect results.
Placing the 78% figure among other numbers
Different documents from the same project do not match perfectly, and readers should know it. The Alzheimer’s Association conference release gives a 78% ten-year risk for the very high group and also notes that its data may differ from the abstract. It lists about 2,700 participants and 518 progression events in places where the Mass General Brigham account says 2,684 and about 478. The materials do not explain the gaps, so the published paper should be consulted before any single figure is quoted. The 78% ten-year estimate itself appears in both the university release and the conference materials.
Follow-up ran for years in some cohorts and far less in others, which is the practical reason the ten-year number is shakier: fewer participants were observed for a full decade, so a small number of cases can move the estimate a long way. The five-year figure rests on much more data. The study measured absolute risk over limited windows in a volunteer population. The authors list selection bias as a limitation, since people in research cohorts may differ from the general population, and they say validation in broader, more representative groups is needed. Lifetime risk was not estimated.
The FDA-cleared test, the missing treatment and the caution
Funding came from 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 an anonymous foundation. Sperling disclosed consulting for pharmaceutical and biotech companies and trial funding from Eisai and Eli Lilly outside the submitted work, which is standard disclosure but relevant given that both firms sell Alzheimer’s drugs.
In May 2025 the Food and Drug Administration cleared the Lumipulse plasma ratio test from Fujirebio, a blood test for adults 55 and older who already show signs and symptoms of Alzheimer’s disease in specialized care. It is not a screening test. The new analysis asks a different question, about people with no symptoms, and the authors do not endorse testing them.
Sperling said in the EurekAlert release that currently available blood tests are not recommended for people without symptoms, because no disease-modifying treatments yet exist for people found to be at high risk. Advice after a high result stays the same: exercise, eat well and prioritize sleep. The researchers see the nearer-term use as selecting volunteers for prevention trials, and Sperling described the long-term goal as making these tests as routine for Alzheimer’s risk as cholesterol testing is for heart attack risk. The unresolved question is what a person would do with a high result today. With no approved way to delay impairment in healthy people, a 78% estimate is information that currently has no matching treatment.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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