Blood Test “Clocks” Predict Start of Alzheimer’s Symptoms
Posted on 20 Feb 2026
More than 7 million Americans live with Alzheimer’s disease, and related health and long-term care costs are projected to reach nearly USD 400 billion in 2025. The disease has no cure, and symptoms often appear only after years of silent brain changes driven by amyloid and tau protein buildup. Researchers have now developed a predictive model that uses a single blood test to estimate when Alzheimer’s symptoms are likely to begin, potentially years before clinical signs emerge.
The models, developed by researchers at Washington University School of Medicine in St. Louis (St. Louis, MO, USA), measure plasma levels of p-tau217, a protein fragment associated with amyloid and tau accumulation in the brain. For their study, the researchers analyzed data from 603 cognitively unimpaired older adults enrolled in the Knight Alzheimer's Disease Research Center and the Alzheimer’s Disease Neuroimaging Initiative.
Plasma p-tau217 levels were assessed using clinically available and FDA-cleared tests. Because p-tau217 reflects underlying amyloid and tau pathology, the researchers used its levels to estimate the biological “clock” of disease progression and predict when symptoms would likely appear. The predictive models estimated the age of Alzheimer’s symptom onset within a margin of three to four years. Elevated p-tau217 levels were strongly associated with future symptom development.
The analysis revealed that age influenced disease trajectory. Individuals with elevated p-tau217 at age 60 developed symptoms roughly 20 years later, whereas those with elevated levels at age 80 developed symptoms about 11 years later. The model performed consistently across different p-tau217 diagnostic platforms, supporting its robustness and generalizability.
The findings, published in Nature Medicine, suggest that blood-based prediction models could make preventive clinical trials more efficient by identifying individuals likely to develop symptoms within defined timeframes. In the long term, such tools may help patients and physicians plan strategies to delay or prevent cognitive decline. Researchers have shared their model code publicly and developed a web-based application to facilitate further refinement. Future studies aim to integrate additional blood biomarkers to improve prediction accuracy for individual clinical use.
“Our work shows the feasibility of using blood tests, which are substantially cheaper and more accessible than brain imaging scans or spinal fluid tests, for predicting the onset of Alzheimer’s symptoms,” said senior author Suzanne E. Schindler, MD, PhD. “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.”
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