Blood test predicts Alzheimer’s ten years before symptoms

Researchers analysed blood samples from 2,684 older adults who showed no signs of memory or thinking problems at enrolment. They measured levels of p-tau217, a protein found in the blood that is linked to Alzheimer's disease, and followed participants for years afterwards. The study, published in a leading medical journal, pooled data from six studies conducted across North America, Japan, and Australia.

How large is the risk?

Among people with very high p-tau217 levels, the estimated probability of developing cognitive impairment within five years was 38 percent. Over ten years, that figure rose to an estimated 78 percent. The researchers emphasise that far fewer observations were available for the longer time horizon, making those estimates less certain.

Crucially, p-tau217 added predictive value beyond already established risk factors. Even after accounting for sticky protein build-up detected on brain scans and genetic risk factors such as carrying a gene variant that raises Alzheimer's risk, the biomarker remained clearly associated with future memory and thinking decline.

Not yet ready for routine screening

The researchers are clear: the test is not currently recommended for routine screening of people without symptoms. Disease-modifying treatments that could change the course of Alzheimer’s in asymptomatic individuals at elevated biological risk have not yet been established. Medical advice remains the same regardless of test results: exercise regularly, prioritise sleep, and maintain a healthy diet.

The team does see potential once preventive therapies are validated. If ongoing trials show that disease-modifying treatments benefit people identified at an early biological stage, p-tau217 could help select those most likely to respond. The researchers draw an analogy: just as cholesterol measurement guides heart disease prevention today, p-tau217 could one day guide dementia prevention.

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