Doctors still advise healthy people against this Alzheimer’s blood test, even though at its highest levels it predicted a 78% chance of decline in 10 years
Blood tests for Alzheimer’s disease have moved from research labs toward the clinic, and one has already received clearance from US regulators. They measure a protein called p-tau217, which rises as the disease develops in the brain. Researchers at Mass General Brigham pooled six studies from North America, Japan and Australia, covering 2,684 older adults whose memory and thinking were normal when they gave blood. They tracked who developed cognitive impairment in the years that followed.
Higher levels of p-tau217 predicted who would decline. Among people with very high levels, the estimated chance of developing cognitive impairment was 38% within five years and 78% within 10 years. Overall, about 478 participants developed impairment during follow-up.
The researchers stress that the 10-year estimate rests on much less data than the five-year figure, so it is less certain.
The blood test added information beyond what doctors already use. It predicted decline even after accounting for amyloid plaques seen on PET brain scans and for APOE4, the strongest known genetic risk factor for late-onset Alzheimer’s.
“What really sets this work apart is that it estimates an individual’s level of risk for cognitive impairment,” said lead author Rachel Buckley of the Mass General Brigham Neuroscience Institute.
The second finding is the one most people will not expect: the researchers do not recommend the test for people without symptoms. “We do not yet have disease-modifying treatments for people who find out they are at high risk for developing cognitive impairment due to Alzheimer’s disease, which is why we don’t recommend currently available blood tests for asymptomatic individuals,” said senior author Reisa Sperling. “Today, our medical advice would remain the same regardless of test results: exercise regularly, maintain a healthy diet, and prioritize sleep and overall wellness.”
That could change. Several trials are testing whether treatments given before symptoms appear can slow the disease. If they work, Sperling says, the goal is to make this test work like a cholesterol test does for heart attacks.
p-tau217 has shown up in our coverage before, in a study linking belly fat in midlife to Alzheimer’s proteins in the blood decades later. Other routine blood measures, such as hemoglobin, have also been tied to later dementia risk.
For people curious about getting tested, the practical advice is to talk to a doctor first about what a result would change. For now, a high reading mainly opens the door to joining a prevention trial.
There are limits to what this shows. Participants in research cohorts are not fully representative of the general population, and the study predicts risk over set periods, not lifetime risk. Several authors report consulting or funding ties to drug companies developing Alzheimer’s treatments, including Eli Lilly and Eisai, which partly funded the underlying studies. The study was published in JAMA after being presented at the Alzheimer’s Association International Conference.
Source
Buckley RF, Townsend DL, Birkenbihl CJ, et al. “Prognostic Value of Blood-Based P-Tau217 Levels for Progression to Cognitive Impairment.” JAMA, 2026.
DOI: 10.1001/jama.2026.12556
