Blood test predicts Alzheimer's onset with over 90% accuracy

Blood test predicts Alzheimer's onset

A new blood test can predict whether and when a person will develop Alzheimer's disease. The test measures levels of a key protein in the blood that correlate with the progression of the disease years before symptoms appear.

Researchers found the test could forecast the onset of Alzheimer's with over 90% accuracy. This represents a significant advance toward a simple, accessible tool for early detection and intervention.

How the protein clock works

The test focuses on phosphorylated tau, specifically a form called p-tau217. This protein is a core component of the toxic tangles that accumulate in the brains of people with Alzheimer's.

Levels of p-tau217 in the blood rise in a predictable pattern as the disease progresses. This pattern allows researchers to estimate the timeline of brain changes, functioning as a biological clock for Alzheimer's pathology.

"We could use these biomarkers to identify people who are likely to progress to Alzheimer's disease and when they will develop clinical symptoms," said study co-author Oskar Hansson of Lund University.

Study tracked disease progression for years

The research, published in Nature Medicine, analyzed data from 1,325 participants across three international cohorts. Scientists tracked individuals over time, comparing blood p-tau217 levels with advanced brain scans and cerebrospinal fluid tests.

They found that the blood test could predict Alzheimer's development up to eight years before diagnosis. The model could also estimate the time to symptomatic onset within a window of a few years.

This predictive power was consistent across different study groups, strengthening the validity of the findings.

New tests are already changing diagnosis

This research builds on the recent arrival of the first approved blood tests for Alzheimer's. These tests, which also detect abnormal tau or amyloid proteins, are beginning to transform clinical practice.

Previously, confirming Alzheimer's pathology required expensive PET scans or invasive spinal taps. Blood tests offer a far more accessible and scalable alternative.

• Quest Diagnostics offers a direct-to-consumer blood test measuring p-tau217.
• ALZpath and C2N Diagnostics have developed similar lab-based tests.
• These tests are used to detect the presence of Alzheimer's pathology, not yet to predict timing.

Accuracy and accessibility challenges remain

While promising, experts caution that predictive timing models require further validation in more diverse populations. The current study participants were predominantly white and highly educated.

"The idea of a clock is intriguing, but we need to see if this works in real-world clinical settings," said Rebecca Edelmayer, senior director of scientific engagement at the Alzheimer's Association.

Another challenge is ensuring equitable access. Widespread use of predictive blood tests must be paired with clear guidelines and available treatments to be ethically sound.

A tool for the new treatment era

The development of disease-predicting blood tests coincides with the arrival of the first drugs that can modestly slow Alzheimer's progression, such as lecanemab (Leqembi).

These treatments are most effective when administered early in the disease course. A test that identifies people at high risk years in advance could allow for earlier therapeutic intervention.

"This could really help us enroll the right people in clinical trials at the right time and eventually guide treatment decisions," Hansson said.