How a Blood Test May Predict Your Risk for Cognitive Impairment Due to Alzheimer’s Disease

Key takeaways

New research from Mass General Brigham Neuroscience Institute found that a simple blood test could predict cognitive decline accurately. Before you rush to your doctor to ask for an Alzheimer’s blood test:

• Discuss your personal risk factors for Alzheimer’s disease with your doctor. If you don’t have symptoms of cognitive decline, the new blood test might not be appropriate for you.
• Don’t be tempted by online biomarker tests. Experts warn that biomarker test results without the insight of a medical professional can be confusing and alarming.
• Follow recommendations for overall brain health as your best option to prevent Alzheimer’s disease as research continues.
• Learn about the latest groundbreaking research into Alzheimer’s diagnosis, treatment, and prevention from the world-renowned experts at Mass General Brigham Neuroscience Institute.

A recent international study led by Mass General Brigham memory disorders experts shows that a blood test may predict your odds of developing memory loss or thinking problems (cognitive impairment) in the future.

The blood test measures phosphorylated tau 217 (p-tau217), a biomarker of Alzheimer’s disease. The study found that cognitively healthy adults with high p-tau217 levels were at greater risk for cognitive impairment and Alzheimer’s disease. Cognitive decline also happened at a faster rate.

“This information may help health care providers more accurately gauge Alzheimer’s disease risk years before symptoms appear,” says Rachel Buckley, PhD, a cognitive neuroscientist at the Mass General Brigham Neuroscience Institute and lead author of the study, which was published in JAMA.

Despite these findings, the time isn’t right for universal Alzheimer’s disease screenings, says Reisa Sperling, MD, director of the Mass General Brigham Center for Alzheimer Research and Treatment and senior author of the JAMA study.

“Until we have treatments to slow or stop the onset of Alzheimer’s disease in people who do not yet show symptoms, biomarker testing in asymptomatic adults should only be used in clinical research,” Dr. Sperling says. “Right now, the blood test results would not change our recommendations to focus on a healthy lifestyle.”

Still, the study findings are critical to understanding disease onset, early detection, and the development of disease-modifying treatments. Here, Drs. Buckley and Sperling explain what these findings mean for your brain health.

What is the role of p-tau217 in Alzheimer’s disease?

Everyone has tau. This protein supports nerve cells and helps carry nutrients along pathways in your brain. In Alzheimer’s disease, tau undergoes a chemical change called phosphorylation. Abnormal p-tau217 proteins stick together, creating strands that tangle in the brain. These tangles stop nutrients from moving through the nerve pathways. The changed cells collapse and die.

Clumps or plaques of amyloid-beta (another protein that changes when you have Alzheimer’s disease) also form in the brain. Tau tangles and amyloid plaques are the two major hallmarks of Alzheimer’s disease.

How does p-tau217 affect your brain health?

The JAMA study explored the preclinical or pre-impairment stage of Alzheimer’s disease. During this first stage, tau tangles and amyloid plaques start to form. But these changes don’t yet affect your memory or thinking.

For the JAMA study, a group of researchers looked at p-tau217 levels in close to 2,700 cognitively healthy adults aged 60 and older. The adults participated in six different research studies dating back to 2004. The study found that participants with very high levels of p-tau217 (defined as more than twice the average level) had:

• 38% absolute risk of cognitive impairment over the next 5 years
• 78% absolute risk of cognitive impairment over the next 10 years

In comparison, people with slightly elevated p-tau217 levels (defined as just above average) had:

• 15% chance of cognitive impairment over the next 5 years
• 45% chance of cognitive impairment over the next 10 years

“Absolute risk indicates the likelihood of actually progressing to cognitive impairment over set time frames when factoring in certain parameters,” says Dr. Buckley. “Our study considered p-tau217 levels along with a person’s age, biological sex, and education levels. Future studies will also include health factors or comorbidities, such as high blood pressure and diabetes, which can affect brain health.”

Researchers also included results from positron emission tomography (PET) scans. These brain imaging scans, along with lumbar punctures (spinal taps) to measure tau protein and amyloid-beta-42 peptide, are currently the gold standard for diagnosing Alzheimer’s disease. But these tests are more invasive than a blood test. And they don’t typically take place until a person shows signs of cognitive impairment.

“In our study, the blood test was more informative and predictive of Alzheimer’s disease risk than PET scans and known genetic risk factors,” says Dr. Buckley.

Should you take an Alzheimer’s disease blood test?

Since 2025, the U.S. Food and Drug Administration (FDA) has approved four biomarker blood tests for Alzheimer’s disease. The most recently approved test, Elecsys®, measures only p-tau217 levels in plasma, the liquid part of blood. But the Alzheimer’s Association and other experts advise against testing if you don’t have symptoms and aren’t participating in a research study.

FDA-approved tests require a doctor’s prescription. But Medicare and private health insurers are unlikely to cover the costs, which can range from $200 to $1,500, if you don’t have symptoms. In fact, Medicare doesn’t even cover the costs for patients with symptoms. The bipartisan Alzheimer’s Screening and Prevention (ASAP) Act seeks to change that. However, the legislation, introduced in 2025, is still awaiting congressional approval.

While you can purchase at-home biomarker tests online, their accuracy and reliability vary. “I don’t recommend online tests because the results can be confusing and alarming without the right support from a knowledgeable health care provider or research study,” says Dr. Sperling.

What research is underway to help those at risk for Alzheimer’s disease?

More than 7 million Americans have Alzheimer’s disease, according to the Alzheimer’s Association. The organization predicts that number will almost double by 2060 if preventive treatments don’t become available.

“Biomarker measurements are important for research studies focused on finding ways to slow or stop the disease,” says Dr. Sperling. “We also need accurate tools for assessing risk and determining who can benefit from preventive treatments when they become available.”

Anti-amyloid treatments are now available to slow the buildup of amyloid plaques in people in the early symptomatic stages of Alzheimer’s disease. Dr. Sperling is co-principal investigator of the AHEAD Study, the first clinical trial to test an FDA-approved anti-amyloid drug called lecanemab (LEQEMBI®) as a therapy for asymptomatic people with increased levels of amyloid to prevent memory loss. Other studies, including trials of new drugs to lower p-tau217 levels, are also underway.

Once preventive treatments become available, Dr. Sperling says testing for Alzheimer’s disease biomarkers could become as routine as measuring cholesterol to predict heart disease risk.

“The goal is to have medications that decrease plaques and tangles in patients at high risk for developing dementia just as we have cholesterol-lowering medications that lower heart attack risk,” Dr. Sperling says.