Alzheimer Blood Tests Can Predict Disease Risk a Decade Early, Study Finds
A large international study published July 15 in the Journal of the American Medical Association and presented at the Alzheimer’s Association International Conference (AAIC) in London has produced the strongest evidence yet that a simple blood test can predict a person’s risk of developing Alzheimer’s-related cognitive impairment up to a decade before symptoms emerge. The findings mark a pivotal shift in Alzheimer’s care — from diagnosing the disease after symptoms appear to forecasting risk years in advance.
The Study and Its Findings
Led by researchers at the Mass General Brigham Neuroscience Institute, the study pooled data from 2,684 cognitively healthy older adults across six observational studies and clinical trials in North America, Japan, and Australia. Participants had an average age of 70 and were followed for nearly five years on average, with some tracked for more than a decade. During the study period, approximately 478 participants progressed to cognitive impairment.
The researchers measured blood levels of p-tau217, a phosphorylated form of the tau protein that accumulates in the brain as Alzheimer’s pathology develops. According to the AAIC press release, cognitively healthy older adults with very high p-tau217 levels — more than twice the average — had an estimated 38% risk of developing cognitive impairment within five years and up to 78% risk within ten years. Those with moderately elevated levels faced approximately 15% risk over five years and 45% risk over ten years.
“Our findings provide 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,” said Dr. Rachel F. Buckley, lead author and associate chair of research at the Mass General Brigham Neuroscience Institute and associate professor of neurology at Harvard Medical School, as reported in the Mass General Brigham press release.
A New Dimension in Alzheimer’s Testing
What sets this study apart from prior research is its focus on risk prediction rather than mere diagnosis. Previous work had already established that p-tau217 blood tests can reliably identify Alzheimer’s-related brain changes in symptomatic patients. The FDA has cleared two such tests: Fujirebio’s Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio (cleared May 2025) for symptomatic adults in specialized care, and Roche’s Elecsys pTau181 for initial rule-out assessment in primary care.
This new research adds a forward-looking dimension. The blood test provided predictive information independent of what brain scans (amyloid PET) and genetic testing (APOE4) can offer, according to the study authors. As Dr. Reisa Sperling, senior author and neurologist at Mass General Brigham, explained: “Our long-term goal is to get us to where cholesterol testing is in predicting your risk of a heart attack.”
Implications for Treatment and Prevention
The ability to identify high-risk individuals years before symptoms appear could dramatically accelerate clinical trials for preventive treatments. Currently, disease-modifying therapies like lecanemab and donanemab are approved only for patients who already have mild cognitive impairment or early dementia. No treatments have yet been proven effective for asymptomatic individuals at high risk.
“Once verified, these blood tests could be used to recruit patients for clinical trials of treatments to prevent cognitive decline and dementia,” Buckley said. Dr. Maria C. Carrillo, chief science officer of the Alzheimer’s Association, called the development “the future of Alzheimer’s care,” adding that targeting the disease in its silent stage “is when treatments may have the greatest benefit — perhaps even keeping people from ever experiencing dementia symptoms.”
Caution and Current Guidance
Despite the promise, researchers and clinicians urge caution. The Alzheimer’s Association and American Academy of Neurology currently recommend p-tau217 testing only for symptomatic patients being evaluated for cognitive impairment, not for general population screening of asymptomatic individuals.
“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,” 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.”
Limitations and the Road Ahead
The test detects Alzheimer’s pathology, not symptoms. Amyloid pathology is found in roughly 30% of cognitively normal older adults, many of whom never develop clinical Alzheimer’s. Test performance can also be affected by chronic kidney disease, obesity, and other comorbidities. Additionally, the test does not distinguish Alzheimer’s from other forms of dementia such as LATE, Lewy body disease, or frontotemporal dementia.
Researchers emphasized that more diverse study populations and longer follow-up periods are needed to refine risk estimates. The Centers for Medicare & Medicaid Services is expected to issue a national coverage determination for FDA-cleared plasma Alzheimer’s biomarkers in late 2026, which could significantly expand access to testing.
As Healthcare Discovery noted, the arrival of a blood test for Alzheimer’s “does not cure the disease. It does not by itself prevent it. What it does is collapse a diagnostic process that has been opaque, expensive, and often inaccessible into something a primary care physician can order with a routine blood draw.”
For the estimated 7.4 million Americans age 65 and older living with Alzheimer’s today — a number projected to reach 13.8 million by 2060 — that change represents the beginning of a new era in how the disease is understood, detected, and ultimately confronted.