Study shows a blood test can help identify healthy people at high risk
for Alzheimer's disease
[July 15, 2026]
By LAURAN NEERGAARD
WASHINGTON (AP) — A blood test may predict if apparently healthy older
adults are likely to develop Alzheimer’s symptoms in the next five or 10
years, researchers reported Wednesday.
That information could be reassuring or terrifying, but for now it's a
potential tool to speed drug development by helping to identify and
enroll high-risk people into studies of possible Alzheimer's treatments
or preventive strategies.
Already large clinical trials are testing if certain drugs could prevent
or at least delay the disease — and if any of those pan out, doctors
will need an easy way to tell who should try them.
The scientists behind the new study stress that it’s too soon for
healthy people to seek out the so-called p-tau217 test, which is
currently used to help diagnose whether people experiencing cognitive
problems have Alzheimer’s or another disorder.
“Wait and get tested when you can potentially do something about it,”
stressed Dr. Reisa Sperling of the Mass General Brigham Neuroscience
Institute, the study’s senior author. “At this point it wouldn’t change
what I would tell someone to do. I’d still tell them to eat well, sleep
well, exercise a lot and stay engaged.”
The new findings showed that symptom-free older adults who harbored very
high levels of p-tau217 had a 38% risk of developing cognitive
impairment over five years. That risk grew to 78% by 10 years.
The research was published in JAMA and presented at the Alzheimer’s
Association International Conference in London.
It’s not clear exactly what causes Alzheimer’s, but its telltale markers
are brain-clogging amyloid plaques and neuron-killing tau tangles. The
p-tau217 test measures a form of tau that correlates with how much
plaque buildup someone has and gives a hint about tangles, Sperling
said.
The Mass General Brigham team analyzed data from 2,684 older adults who
were healthy when they’d joined some long-running Alzheimer’s studies,
receiving the p-tau217 blood test at enrollment and yearly cognitive
checkups. Between the earliest enrollment in 2004 and last year, about
478 had developed cognitive impairment.
Study participants with very low p-tau217 levels likewise had a low risk
of developing cognitive impairment over the five- to 10-year period.
There’s a conundrum in predicting Alzheimer’s: Lots of people harbor
high levels of amyloid plaques yet never get dementia. A leading theory
is that at some point amyloid buildup triggers an abnormal type of tau
to form tangles, leading to symptoms.
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A human brain affected by Alzheimer's disease is displayed at the
Museum of Neuroanatomy at the University at Buffalo in Buffalo,
N.Y., on Oct. 7, 2003. (AP Photo/David Duprey, File)
 Sperling said the blood test data
offers some new clues. While different intermediate levels of
p-tau217 signaled progressive risk, only the very highest level
seemed to correlate with other evidence about that tipping point.
“This is a gradual process where amyloid and tau build up in the
brain and this blood-based biomarker is telling you how far you are
in that process,” she said.
Scientists not involved in the study praised it but also offered
some reasons to be cautious. One is that only a small fraction of
study participants had been tracked for a full decade, so there's
less confidence in the 10-year risk estimate than the five-year risk
estimate.
Also, the predictions could be clouded by other factors — older
people may be at risk of dying from something else, or have
heart-related problems that can cause vascular dementia rather than
Alzheimer’s, noted Drs. Suzanne Schindler of Washington University
in St. Louis and David Wolk of the University of Pennsylvania in a
commentary published in JAMA.
The blood tests “are not yet precise enough to guide individualized
prognosis,” wrote Schindler, who also studies p-tau217’s prognostic
potential, and Wolk. Still, they said the new work has “provided a
crucial piece of the puzzle.”
Already “we have people coming saying, ‘I want this blood test. I
have a family history of Alzheimer’s disease,’” said Jessica
Langbaum of the Banner Alzheimer’s Institute in Phoenix, something
she strongly discourages — for now.
“These findings are quite strong,” Langbaum added, and a predictive
blood test would be “really important” — but only if ongoing studies
eventually find a drug that could help people before symptoms begin.
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