A blood test measuring a protein called phosphorylated tau 217 (p-tau217) can predict whether cognitively healthy older adults will develop memory problems and cognitive decline within 5 to 10 years, according to new research presented at the Alzheimer's Association International Conference. The findings suggest this simple test could eventually help doctors identify people who might benefit from preventive therapies before their thinking and memory begin to fail.

Can a Blood Test Really Predict Alzheimer's Years in Advance?

Researchers from Mass General Brigham Neuroscience Institute analyzed data from 2,684 cognitively healthy older adults across six studies conducted in North America, Japan, and Australia. All participants underwent blood testing for p-tau217 and brain imaging when they enrolled. Over the following years, 478 of these participants developed cognitive impairment.

The results were striking. Among people with very high p-tau217 levels at the start of the study, approximately 38 percent developed cognitive impairment within 5 years. When researchers extended their projections to 10 years, that risk climbed to as much as 78 percent. By contrast, those with lower p-tau217 levels remained cognitively healthy.

"The main takeaway is that very high levels of plasma p-tau217 provide meaningful information about future risk of cognitive impairment among older adults who are initially cognitively unimpaired," explained Rachel Buckley, a cognitive neuroscientist with the Mass General Brigham Neuroscience Institute.

Rachel Buckley, Cognitive Neuroscientist, Mass General Brigham Neuroscience Institute

What makes this test particularly valuable is that it appears to work independently of other known Alzheimer's risk factors. Even after accounting for amyloid plaques detected on brain scans and genetic risk factors like the APOE4 gene variant, the p-tau217 blood test still predicted future cognitive decline. This suggests the test captures something important about Alzheimer's disease biology that other measures might miss.

Why Isn't This Test Available to Everyone Right Now?

Despite these encouraging findings, researchers emphasize that the test should not yet be used to screen healthy people without cognitive symptoms. The critical limitation is simple: there are currently no proven disease-modifying treatments that can prevent Alzheimer's-related cognitive decline in people identified as high-risk through blood testing alone.

Identifying someone at risk years before symptoms appear would only be helpful if doctors had an effective treatment to offer them. Right now, the only recommendations for older adults remain lifestyle measures that support overall brain health. However, this situation could change rapidly if ongoing clinical trials demonstrate that earlier treatment can delay or prevent Alzheimer's symptoms.

"I am optimistic that anti-amyloid therapies might be right around the corner for cognitively unimpaired individuals, and once this becomes our new reality, we will be absolutely thinking about early detection with markers such as plasma," Buckley noted.

Rachel Buckley, Cognitive Neuroscientist, Mass General Brigham Neuroscience Institute

How to Support Brain Health While Waiting for Prevention Treatments

Until disease-modifying treatments become available for asymptomatic people at high risk, the standard recommendations for maintaining cognitive health remain unchanged. These evidence-based approaches can help protect your brain as you age:

• Regular Physical Activity: Exercise supports blood flow to the brain and may help reduce the accumulation of harmful proteins associated with Alzheimer's disease.
• Healthy Dietary Patterns: Following a balanced diet rich in vegetables, fruits, whole grains, and lean proteins provides nutrients that support brain function and reduce inflammation.
• Adequate Sleep: During sleep, the brain clears out metabolic waste products, including some of the proteins that accumulate in Alzheimer's disease.
• Mental Stimulation: Staying mentally active through reading, learning new skills, puzzles, and social engagement helps maintain cognitive reserve and brain plasticity.

What About Viruses and Alzheimer's Risk?

While the p-tau217 blood test offers a way to identify risk, researchers are also uncovering environmental factors that may contribute to Alzheimer's development. A new study from Cardiff University found that herpesvirus infections, which can remain dormant in the body for years, may accelerate cognitive decline in people already vulnerable to Alzheimer's disease.

The research used mice genetically prone to Alzheimer's-like disease and infected them with a herpesvirus. The scientists discovered that immune cells called T cells, which fight the virus, entered the brain and appeared to speed up cognitive decline and the accumulation of harmful proteins. When researchers blocked the immune response or treated the infection with antiviral medication, the mice performed better on memory tests.

"Not only does this research broaden the understanding of the link between herpesviruses and Alzheimer's disease and further strengthen the link between viruses and dementia more generally, but it raises the importance of prevention of infectious disease and how this, in the long term, may prevent or delay dementia onset," stated Dr. Mathew Clement of Cardiff University School of Medicine.

Dr. Mathew Clement, School of Medicine, Cardiff University

This finding suggests that preventing common viral infections through vaccines and other preventive measures might play a role in reducing dementia risk later in life. The research indicates that dementia risk is not simply determined by genetics, but also by environmental factors including exposure to infections.

Are New Alzheimer's Treatments on the Horizon?

Beyond early detection, researchers are making progress on new treatments that target the proteins driving Alzheimer's disease. An investigational drug called diranersen (BIIB080) showed promising results in a phase 2 trial by reducing tau protein levels in the brain and showing evidence of slowing cognitive decline in people with early Alzheimer's disease.

The drug works by reducing the production of tau protein itself, rather than simply clearing it away. In the trial, all three doses of diranersen produced substantial reductions in tau levels in cerebrospinal fluid, with levels falling by 50 to 65 percent from baseline. Brain imaging showed unprecedented reductions in tau accumulation, particularly in brain regions most affected by Alzheimer's disease.

On cognitive tests, the lowest dose of diranersen slowed decline by 26 percent on one measure and 42 to 50 percent on others, compared with placebo. Although the trial did not meet its primary endpoint of showing a dose-response relationship, the consistent cognitive benefits across multiple measures suggest the drug may help slow disease progression.

"This is the first randomized phase 2 trial of a tau-targeting agent to show that a reduction in tau pathology, which has been clearly and consistently shown across both trials, may slow early Alzheimer's progression," explained Catherine Mummery, professor of clinical neurology at the University College London Queen Square Institute of Neurology.

Catherine Mummery, Professor of Clinical Neurology, University College London Queen Square Institute of Neurology

The drug was generally well tolerated, with most side effects being mild to moderate. The most common adverse events were related to the administration method, which involves injecting the drug directly into the spinal fluid through a lumbar puncture procedure. In 2025, the FDA granted Fast Track designation to diranersen, a status that accelerates development and review of promising treatments for serious conditions.

The convergence of these advances, from early detection through blood tests to new tau-targeting treatments, suggests that the approach to Alzheimer's disease may be shifting. Rather than waiting for symptoms to appear, doctors may soon be able to identify people at high risk years in advance and offer preventive treatments to slow or stop cognitive decline before it begins.