A blood test may help identify healthy older adults who face a higher risk of developing Alzheimer’s-related cognitive impairment within the next five to 10 years, according to a new study.
Researchers found that symptom-free older adults with very high levels of the blood biomarker p-tau217 had a 38% risk of developing cognitive impairment within five years. Their estimated risk rose to 78% over 10 years, although researchers cautioned that the 10-year estimate is less certain.
The findings were published in JAMA and presented at the Alzheimer’s Association International Conference in London.
The test is not being recommended for routine screening in healthy people. Researchers said its main value for now is helping identify high-risk participants for clinical trials that are testing whether certain drugs can prevent or delay Alzheimer’s disease before symptoms appear.
“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 Dr. Reisa Sperling, senior author of the study and a neurologist with the Mass General Brigham Neuroscience Institute.
She said the standard medical advice remains the same regardless of test results. That includes regular exercise, a healthy diet, quality sleep, and overall wellness.
The international study combined data from six observational and clinical trial cohorts in North America, Japan, and Australia.
Researchers analyzed 2,684 cognitively healthy older adults who received p-tau217 blood testing and annual cognitive assessments. Participants also underwent PET brain imaging when they enrolled.
The earliest participants entered one of the studies in 2004. The most recent follow-up took place in 2025. About 478 participants developed cognitive impairment during the follow-up period.
Higher p-tau217 levels at the start of the study were linked to a greater chance of future cognitive decline. Participants with very low levels of the biomarker had a much lower risk over the following five to 10 years.
The blood test also predicted future cognitive impairment independently of other known Alzheimer’s risk factors. Those included amyloid-beta plaques detected on PET scans and the APOE4 genetic variant.
Alzheimer’s disease is marked by the buildup of amyloid plaques and tau tangles in the brain. The p-tau217 test measures a form of tau protein tied to those disease-related changes.
Researchers said the test may help show how far a person is in the disease process before symptoms appear.
Lead author Dr. Rachel F. Buckley said the study is notable because it estimates a person’s future risk of cognitive impairment, rather than simply linking the biomarker to Alzheimer’s disease.
The study had limitations. Fewer participants were followed for a full decade, making the 10-year estimate less reliable than the five-year finding. Researchers also said the results need to be confirmed in broader and more representative populations.
Outside experts urged caution.
In an accompanying JAMA commentary, Dr. Suzanne Schindler of Washington University in St. Louis and Dr. David Wolk of the University of Pennsylvania wrote that blood tests are “not yet precise enough to guide individualized prognosis.”
They also noted that some older adults may develop other forms of dementia, such as vascular dementia, or die from unrelated causes before Alzheimer’s symptoms appear.
Still, researchers said p-tau217 testing could help speed Alzheimer’s prevention trials by identifying healthy people who are more likely to develop symptoms.
Sperling said the long-term goal is for the test to become as useful as cholesterol testing is for assessing heart disease risk. If prevention trials show that early treatments can help, the blood test could eventually guide earlier monitoring or intervention.