July 29, 2026
A blood test may predict your risk of developing Alzheimer’s disease up to 10 years before memory loss and other symptoms arise, researchers report. The test is not currently recommended for routine use in adults with healthy memories, but it could pave the way for identifying people at high risk of developing Alzheimer’s and testing new preventive therapies for the disease.
The test measures blood levels of a substance called phosphorylated tau 217, or p-tau217. The substance is a form of the toxic protein tau, a hallmark of Alzheimer’s, which forms spaghetti-like tangles inside neurons as the disease progresses, disrupting communication between brain cells and causing cell death.
For the study, researchers at Mass General Brigham and other institutions pooled data from 2,684 older men and women who were enrolled in six long-running studies in North America, Japan and Australia. They included well known research initiatives such as the Harvard Aging Brain Study and the Alzheimer’s Disease Neuroimaging Initiative. All were free of serious memory problems at the start of the study. Their average age was around 70.
Researchers measured their blood p-tau217 levels and conducted PET scans of their brains to look for signs of Alzheimer’s disease at the start of the study period. Over the next 10 plus years, researchers performed regular tests of memory and thinking skills to look for signs of cognitive impairment. During that time, some 478 of the participants developed serious memory problems.
The researchers calculated that people who had very high levels of p-tau217 at the start of the study had a 38 percent risk of developing cognitive impairment over the next five years. After 10 years, the risk grew to 78 percent, though these longer-term estimates were based on limited data.
Researchers found that the blood test predicted risk independent of other known Alzheimer’s risk factors, including the buildup of beta-amyloid plaques in the brain and known genetic risk factors like carrying the APOE-E4 gene variant. The findings were published in the journal JAMA, from the American Medical Association.
The authors noted that more needs to be learned about the accuracy of blood tests for Alzheimer’s and that until more effective therapies become available to prevent or delay the onset of Alzheimer’s, blood testing would have limited benefits for healthy older adults. “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, the study’s senior author and a neurologist at the Mass General Brigham Neuroscience Institute.
Longer-term, she noted, patients might one day go to their doctor’s office to get an Alzheimer’s blood test, the same way you get a cholesterol test today. “The preventive care landscape could change rapidly if ongoing trials of disease-modifying therapies prove beneficial. In the future, these tests could help identify those who might benefit most from these treatments.”
In the meantime, Dr. Sperling said, “Today, our medical advice would remain the same regardless of test results: Exercise regularly, maintain a healthy diet, and prioritize sleep and overall wellness.”
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, PhD, of The Fisher Center lab at The Rockefeller University.
Source: Rachel F. Buckley, PhD; Diana L. Townsend, PhD; Colin J. Birkenbihl, PhD; e tal: “Prognostic Value of Blood-Based P-Tau217 Levels for Progression to Cognitive Impairment.” JAMA, July 14, 2026
