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• Posted February 20, 2026

Blood Test Estimates When Alzheimer’s Symptoms Will Start

Imagine knowing exactly when your brain might start to fail. 

It sounds like a plot from a futuristic movie, but a new "biological clock" developed by researchers at Washington University School of Medicine in St. Louis may make it a reality.

By analyzing a blood sample, scientists were able to estimate when a person’s Alzheimer’s symptoms would begin, often years before the first signs of forgetfulness appear.

The study, published Feb. 19 in Nature Medicine, focuses on a specific protein in the blood called p-tau217. This protein serves as a marker for the "plaques and tangles" — known as amyloid and tau — that slowly accumulate in the brains of Alzheimer’s patients. 

Researchers found they could use these protein levels to predict the onset of cognitive decline within a narrow margin of 3 to 3.7 years.

The buildup of these toxic proteins follows a remarkably steady and predictable schedule, according to researchers.

“Amyloid and tau levels are similar to tree rings — if we know how many rings a tree has, we know how many years old it is,” lead author Kellen Petersen, an instructor in neurology, said in a news release. 

“It turns out that amyloid and tau also accumulate in a consistent pattern and the age they become positive strongly predicts when someone is going to develop Alzheimer’s symptoms,” he added.

For the study, his team analyzed data from 603 older adults. Their median age was 67.7, meaning half were older, half younger.

Their findings revealed that the brain’s ability to handle amyloid and tau proteins changes as people age. 

For instance, a 60-year-old with elevated protein levels might not show Alzheimer’s symptoms for another 20 years. But an 80-year-old with the same levels might see symptoms in just 11 years, suggesting that older brains have less reserve to fight off the damage.

Currently, identifying Alzheimer’s risk often requires expensive brain scans or invasive spinal taps. This blood test offers a quicker, less costly, more accessible alternative that could change how doctors and scientists approach the disease.

The test is used today mostly in research settings. The researchers made public the details behind their models and a web application for other researchers to explore and build upon.

“In the near term, these models will accelerate our research and clinical trials,” said senior author Suzanne Schindler, an associate professor of neurology. “Eventually, the goal is to be able to tell individual patients when they are likely to develop symptoms, which will help them and their doctors to develop a plan to prevent or slow symptoms.”

Funding partners for the study included AbbVie Inc., Alzheimer’s Association, Diagnostics Accelerator at the Alzheimer’s Drug Discovery Foundation, Biogen, Janssen Research & Development, LLC, and Takeda Pharmaceutical Company Limited. 

More information

The National Institute on Aging has an Alzheimer's Disease Fact Sheet covering symptoms and current research.

SOURCE: Washington University School of Medicine in St. Louis, news release, Feb. 16, 2026