Simple blood test may predict risk of developing dementia up to 10 years before diagnosis
A simple blood test could soon predict a person’s risk of developing dementia up to a full decade before symptoms appear.
The new blood test measures levels of a protein called phosphorylated tau 217 (p‑tau217), a known biomarker for Alzheimer’s disease.
Researchers found that higher levels of this protein in the blood were consistently associated with an increased risk of progressing to cognitive impairment in older adults who were cognitively healthy at the start of the study.
The findings, presented at the Alzheimer’s Association International Conference in London, could transform how doctors screen for and potentially prevent dementia.
If trials confirm that early intervention can delay cognitive decline, this blood test could identify who might benefit most from new drugs that target brain proteins or lifestyle changes years before symptoms appear.
The study followed 2,684 healthy older adults for up to 13.5 years. Over that time, 478 developed cognitive impairment.
Those with very high p-tau217 levels had a nearly 40 percent chance of developing cognitive impairment within five years, compared to 12 percent for low levels. Over ten years, the very high group faced a nearly 80 percent chance.
Experts caution that the test is not yet ready for routine use, but the study marks a significant step toward a future in which a simple blood draw could help predict and potentially stave off one of aging’s most feared conditions.
The test measures blood levels of p-tau217, a protein linked to Alzheimer’s. Elevated levels predict amyloid buildup in the brain with over 90 percent accuracy and signal higher risk of future cognitive decline (stock)
Researchers pooled data from 2,684 cognitively healthy older adults with an average age of 69, across six research studies in North America, Japan and Australia.
Each participant had a blood test measuring levels of p-tau217, which has long been linked to Alzheimer’s disease, and was tracked for the development of cognitive impairment, defined as mild cognitive impairment, dementia or declining scores on a standard dementia rating scale.
Over the nearly 14-year follow-up period, 18 percent of people in the study developed cognitive impairment.
The higher a person’s p-tau217 level, the greater their risk. In addition to a 12 percent risk for those with low levels, the risk was 38 percent for those with very high levels.
Over ten years, the numbers climbed sharply: the low group faced a 40 percent risk, the intermediate group 45 percent, the high group 62 percent and the very high group 78 percent.
People with very high p-tau217 also declined faster on cognitive tests, dropping by −0.07 units per year on a composite memory score, while those with low levels actually improved slightly, likely due to practice effects.
In the study, published in JAMA, authors caution that these estimates come from selected research cohorts, not the general population, and 10-year projections are less reliable because only five percent of participants were followed that long.
‘This is a critical step toward better understanding what p-tau217 can tell us about a person’s risk for cognitive impairment,’ said lead author Dr Rachel F Buckley, a cognitive neuroscientist with the Mass General Brigham Neuroscience Institute.
Survival curves showing how long participants stayed cognitively healthy, grouped by their p-tau217 levels. Those with higher p-tau217 levels progressed to impairment faster.
Absolute risk of developing cognitive impairment at two, five and 10 years by p-tau217 level. By five years, risk ranged from 12 percent (low) to 38 percent (very high). By 10 years, risk ranged from 40 percent (low) to 78 percent (very high)
‘What really sets this work apart is that it estimates an individual’s level of risk for cognitive impairment. We harmonized data across six cohorts, creating a large and varied data set, and still found consistent results showing how p-tau217 informs risk over time.’
Dementia currently affects more than 7 million Americans, including more than 6 million with Alzheimer’s disease.
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In Alzheimer’s disease, two key proteins drive the disease process. The first is amyloid-beta, which clumps into plaques between brain cells.
The second is tau, a protein that normally helps stabilize the internal skeleton of neurons.
In Alzheimer’s disease, tau becomes abnormally hyperphosphorylated, meaning it gains excess phosphate groups, causing it to detach from microtubules and tangle up inside neurons, disrupting cellular function and leading to cell death.
P-tau217 is a specific form of phosphorylated tau. It is notable because it appears to be one of the earliest tau changes detectable in Alzheimer’s, reflecting both amyloid buildup and the early stages of tau tangle formation.
Research shows that p-tau217 is superior to other markers, such as p-tau181, in detecting early biological changes tied to Alzheimer’s.
Studies show that elevated p-tau217 in the blood predicts amyloid buildup on brain scans with over 90 percent accuracy.
It also closely tracks both amyloid and tau accumulation and helps explain how amyloid leads to later tau tangles.
This makes p-tau217 a critical marker for understanding Alzheimer’s progression and a promising tool for predicting future cognitive decline.
Dr Reisa Sperling, senior author and a neurologist at Mass General Brigham Hospital, said: ‘We do not yet have disease-modifying treatments for people who find out they are at high risk for developing cognitive impairment due to Alzheimer’s, which is why we don’t currently recommend blood tests for asymptomatic individuals.
‘Today, p-tau217 can help identify people at high risk for future Alzheimer’s dementia for participation in prevention trials.
‘As these trials move forward, individualized estimates, including the biomarker’s prognostic value, could guide earlier treatment and monitoring decisions.’