Simple Blood Test May Predict Alzheimer’s Years Before Brain Scans Indicate Signs

A new study by Harvard-affiliated investigators at Mass General Brigham has found that a blood test for an Alzheimer’s disease biomarker, plasma phosphorylated tau 217 (pTau217), can predict the progression of the illness years before symptoms appear or brain scan changes are detectable.

The research, published in Nature Communications, followed 317 cognitively healthy older adults from the Harvard Aging Brain Study for an average of eight years. Participants, aged 50 to 90, underwent regular blood tests for pTau217, repeated amyloid and tau PET scans, and long-term cognitive testing. The study found that higher baseline and increasing levels of pTau217 predicted faster buildup of Alzheimer’s pathology—including amyloid plaques and tau tangles in the brain—even when initial brain scans appeared normal.

“We used to think that PET scan detection was the earliest sign of Alzheimer’s disease progression, revealing amyloid accumulation in the brain 10 to 20 years before symptoms appear,” said lead author Hyun-Sik Yang, a Harvard Medical School assistant professor of neurology at Brigham and Women’s Hospital and an associate member of the Broad Institute of MIT and Harvard. “But now we are seeing that pTau217 can be detected years earlier, well before clear abnormalities appear on amyloid PET scans.”

The findings build on prior research, including an NIH-supported study that developed an Alzheimer’s “clock” model using pTau217 blood tests to estimate when symptoms are likely to arise. That research, published in Nature Medicine, analyzed pTau217 levels in over 600 older adults and demonstrated the potential of blood tests to forecast symptom onset.

Last year, the U.S. Food and Drug Administration cleared the first blood test for Alzheimer’s disease, marking a significant step toward making diagnosis more accessible, less invasive, and more affordable than current methods like lumbar punctures or PET scans. The new evidence from Mass General Brigham strengthens the case for using pTau217 blood tests not only to detect existing pathology but to predict future disease progression in people who are still cognitively healthy.

Experts suggest that earlier detection through blood-based biomarkers could improve clinical trial enrollment, allow for timely intervention with emerging therapies, and empower individuals and families to plan for the future. While no cure currently exists for Alzheimer’s, treatments for early symptomatic disease are now available, and ongoing research continues to explore preventive strategies.

As blood-based biomarker tests become more refined and widely available, they may transform how Alzheimer’s is detected, monitored, and managed—shifting the focus toward prevention and early action long before memory loss or confusion begins.