Alzheimer’s blood test flags future symptom risk in study

Alzheimer’s blood test research linked high p-tau217 levels to future cognitive symptoms in healthy older adults. The result may reshape trials.

P-tau217 levels divided risk

Researchers reported Wednesday that a blood marker already used in Alzheimer’s diagnosis may help identify people more likely to show symptoms years before problems appear. The findings were published in JAMA and presented at the Alzheimer’s Association International Conference in London.

The test measures p-tau217, a form of tau associated with Alzheimer’s biology. Alzheimer’s has no single confirmed cause, but researchers track two defining signs of the disease: amyloid plaques that accumulate in the brain and tau tangles that damage neurons.

Five-year risk reached 38%

In the study, symptom-free older adults with very high p-tau217 readings had a 38% risk of cognitive impairment within five years. By 10 years, that risk rose to 78%, according to the research team.

People with very low p-tau217 levels showed low risk across the same five- to 10-year window. The contrast gives researchers a way to separate trial participants by biological risk rather than waiting for memory or thinking problems to emerge.

The Mass General Brigham team examined data from 2,684 older adults who had entered long-running Alzheimer’s studies without cognitive symptoms. Participants received the p-tau217 blood test when they enrolled and then had yearly cognitive evaluations; from the earliest enrollment in 2004 through last year, about 478 developed cognitive impairment.

Trials need faster screening

The near-term use is research, not routine testing for people who feel well. Large clinical trials are already examining whether drugs can prevent or delay Alzheimer’s, and a blood test could make it easier to recruit people at higher risk.

Sperling urges patients to wait

Dr. Reisa Sperling of the Mass General Brigham Neuroscience Institute, the study’s senior author, said healthy people should not rush to seek the test. “Wait and get tested when you can potentially do something about it,” Sperling said.

Her advice reflects the gap between prediction and action. She said the result would not yet change the guidance she gives patients: eat well, sleep well, exercise frequently and stay socially engaged.

The p-tau217 test is already used to help doctors evaluate people who have cognitive symptoms and determine whether Alzheimer’s or another condition may be involved. Applying it to people without symptoms would raise a different set of questions about anxiety, follow-up care and whether a result can lead to a useful intervention.

Drug makers face enrollment test

If prevention trials show that a drug can meaningfully delay symptoms, a test like p-tau217 could become a practical gatekeeper for treatment decisions. Health systems would need rules for who gets screened, Mass General Brigham’s research would become part of the evidence base, and Alzheimer’s drug developers could target studies more efficiently.

Three paths for the assay

If the risk signal holds across broader populations, the global effect would be faster and more selective Alzheimer’s research, with fewer low-risk participants diluting trial results. For the Mass General Brigham team, that would strengthen the clinical relevance of its biomarker work; for the wider diagnostics and drug sector, it would push blood-based screening closer to routine trial infrastructure.

If preventive drugs fail or the test performs unevenly outside research cohorts, p-tau217 would likely remain mainly a diagnostic and research tool. The open questions are concrete: how well the test works across different populations, what threshold should trigger concern, and whether a positive result can guide an intervention that changes a patient’s future.