A blood test that measures a single protein may be able to predict a seemingly healthy person’s risk of developing Alzheimer’s-related cognitive decline up to a decade before any symptoms appear, according to new research.

The findings, presented at the Alzheimer’s Association International Conference (AAIC) 2026 in London, England, found that older adults with very high levels of a biomarker called p-tau217 had roughly a 78 percent chance of developing cognitive impairment within 10 years, even though they showed no signs of memory or thinking problems when tested.

Almost 7 million Americans are living with Alzheimer’s disease today, and that number is projected to nearly double to about 13 million by 2050 if no medical breakthrough changes the trend, according to the Alzheimer’s Association.

‘Tremendous Promise’ but Proceed Carefully

Dr. Manisha Parulekar, co-director of the Center for Memory Loss and Brain Health at Hackensack University Medical Center, New Jersey, told Newsweek the test could transform how doctors approach Alzheimer’s risk.

“A single blood test to detect Alzheimer’s predisposition in cognitively healthy individuals holds tremendous promise,” Parulekar said.

She added that it could move risk assessment “out of specialty clinics and into primary care” and open the door to early, personalized interventions targeting factors such as blood pressure, sleep, hearing and physical activity. It could also speed up recruitment for prevention trials, she said, “enabling us to test whether intervening in the preclinical phase can delay or prevent disease onset.”

psychological distress, anxiety, and anticipatory grief,” and raised concerns about insurance discrimination and unequal access to future care.

“Responsible implementation must pair the test with structured counseling, equitable access to interventions, and robust support infrastructure,” she said.

What the Researchers Found

Researchers had examined blood samples from nearly 2,700 cognitively healthy adults, average age 70, drawn from six major Alzheimer’s research groups and clinical trials. It is among the largest studies of its kind to date. Participants were tracked for an average of nearly five years, with some followed for more than a decade, using standard tests of memory, thinking and daily function.

Adults with p-tau217 levels more than double the study average had an estimated 78 percent risk of cognitive impairment within 10 years, and about a 38 percent risk within five years. Those with moderately elevated levels faced a lower but still notable risk: about 15 percent over five years and 45 percent over 10 years. Notably, the blood test added predictive value beyond what brain scans and genetic testing alone could offer.

P-tau217 is a modified form of the tau protein, which forms tangles in the brain that are a hallmark of Alzheimer’s and are closely tied to cognitive decline. The protein is also linked to levels of amyloid beta, a second hallmark of the disease, making it a useful single marker for both processes.

Study lead author Rachel F. Buckley, associate chair of research at the Mass General Brigham Neuroscience Institute and associate professor of neurology at Harvard Medical School, said in a statement that the results offer “some of the clearest evidence yet that elevated p-tau217 levels may help detect dementia risk years earlier—even in adults with no noticeable memory or thinking problems.”

She said the test could eventually help recruit patients for trials of treatments aimed at preventing cognitive decline.

Researchers stressed that the biomarker alone cannot fully predict an individual’s future risk, since age, genetics, kidney function, obesity and racial and ethnic background can all influence both biomarker levels and dementia risk. They said more diverse study populations and longer follow-up periods are needed to refine long-term risk estimates.

The p-tau217 blood test is FDA-cleared for clinical use in the United States. In May 2025, the U.S. Food and Drug Administration (FDA) cleared the Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio, which is manufactured by Fujirebio, as the first in vitro diagnostic blood test to aid in diagnosing Alzheimer’s disease.

Newsweek has reached out to the study’s authors for more information.

Reference

Buckley, R. F., et al. (2026). Prognostic Value of Blood-Based P-Tau217 Levels for Progression to Cognitive Impairment. JAMA. doi:10.1001/jama.2026.12556.

Contact Newsweek editors on this story: Marc Vargas and James Debens

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