Blood Test Could Predict Alzheimer’s Onset Years Before Symptoms Appear

A simple blood test may soon predict not only a person’s risk of developing Alzheimer’s disease, but also the specific year symptoms will begin, according to groundbreaking new research from Washington University School of Medicine in St. Louis.

The study, published in the journal Nature Medicine, analyzed data from more than 600 older adults enrolled in two long-term Alzheimer’s research projects. Researchers focused on a specific protein called p-tau217, which forms “tangles” in the brain that disrupt communication between nerve cells. In a healthy brain, tau normally helps stabilize nerve cell structure.

By comparing blood samples with participants’ cognitive performance over several years, the team discovered that p-tau217 levels rise in a “remarkably consistent” pattern long before memory loss begins. This pattern allowed them to create a predictive model using a patient’s age and protein levels to estimate when symptoms will appear, with a margin of error of three to four years.

“We show that a single blood test measuring p-tau217 can provide a rough estimate of when an individual is likely to develop symptoms of Alzheimer’s disease,” explained lead author Dr. Kellen K. Petersen, instructor of neurology at Washington University in St. Louis.

The research revealed an important age-related aspect to how quickly symptoms develop after p-tau217 levels become abnormal. “People who first had abnormal p-tau217 levels around age 60 didn’t develop Alzheimer’s symptoms for about 20 years, whereas those who first had abnormal p-tau217 levels around age 80 developed symptoms after only about 10 years,” Petersen noted.

This suggests that both age and disease-related changes in the brain influence the timeline of symptom progression, potentially offering a critical window for early intervention before irreversible cognitive decline occurs.

Currently, brain scans can detect tau tangles when diagnosing Alzheimer’s, but these imaging tests are complex and expensive. A blood test would make monitoring more accessible and cost-effective, potentially transforming both research and clinical practice.

“This could transform how researchers design clinical trials and, eventually, how clinicians identify people at highest risk for cognitive decline associated with Alzheimer’s years before decline begins,” said Dr. Rebecca M. Edelmayer, vice president of scientific engagement at the Alzheimer’s Association, who was not involved in the study. “A blood test is generally much less expensive and easier to administer than a brain scan or spinal-fluid test.”

The study does have limitations. Petersen acknowledged that predictions were only possible for individuals whose p-tau217 levels fell within a certain range. Additionally, the research cohorts were relatively healthy, well-educated, and lacked diversity, potentially limiting how broadly the results apply to the general population.

Despite the promising findings, the researchers strongly caution against individuals seeking out these tests independently. “At this point, we do not recommend that any cognitively unimpaired individuals have any Alzheimer’s disease biomarker test,” warned Dr. Suzanne Schindler, a neurologist at Washington University and co-author of the study.

Petersen emphasized that the current model remains experimental: “The current estimate is not yet accurate enough for clinical use or personal medical decision-making, but we expect that it will be possible to create more accurate models.”

Looking ahead, the research team hopes to refine the test by examining other Alzheimer’s-linked proteins to narrow the margin of error. They also plan to include more diverse participants to confirm and expand upon these results.

The research comes at a critical time in Alzheimer’s treatment. Two large clinical trials are currently underway to determine whether people with high levels of p-tau217 might benefit from early treatment with lecanemab or donanemab — the only approved drugs designed to reduce brain plaques associated with Alzheimer’s disease. Researchers hope that treating patients earlier may significantly boost these drugs’ effectiveness.

“There are many other blood and imaging biomarkers, as well as cognitive tests, that we can combine with plasma p-tau217 to improve the accuracy of predicting symptom onset,” Petersen said. “We hope this work will lead to even better models that will be useful to individuals.”