- Posted April 15, 2026
Blood Test Predicts Alzheimer's Years Before Symptoms, Brain Changes
A blood test can predict Alzheimer’s disease progression in a person’s brain years before they show any symptoms of decline, a new study says.
The test, which looks for a form of toxic tau protein in the blood, reveals Alzheimer’s risk long before brain scans start to show signs of deterioration, researchers reported April 14 in the journal Nature Communications.
The blood test looks for levels of plasma phosphorylated tau 217 (pTau217), a form of tau protein. Tau proteins are known to form toxic tangles in the brains of Alzheimer’s patients, typically later in their decline.
“We used to think that PET scan detection was the earliest sign of Alzheimer’s disease progression, revealing amyloid accumulation in the brain 10 to 20 years before symptoms appear,” said lead researcher Dr. Hyun-Sik Yang, a neurologist at Mass General Brigham Neuroscience Institute in Boston.
“But now we are seeing that pTau217 can be detected years earlier, well before clear abnormalities appear on amyloid PET scans,” he said in a news releae.
If the test is validated through further studies, it could help doctors diagnose Alzheimer’s risk earlier, researchers said. The new Alzheimer’s drugs depend on early detection, and don’t work for patients in advanced decline.
Researchers followed 317 people with brains that were healthy at the outset of the study for an average of eight years. They ranged in age from 50 to 90 years old.
The participants underwent regular blood tests for pTau217 and PET scans looking for amyloid plaques or tau tangles in their brains. They also took cognitive tests to track their brain function.
Results showed that higher levels of pTau217 predicted a faster buildup of plaques and tangles, even if people’s initial brain scans appeared normal.
In fact, increases in pTau217 often happened before any signs of amyloid plaques appeared in people’s brain scans, researchers said.
On the other hand, people with low pTau217 were very unlikely to show the development of any plaques or tangles in their brains during later scans.
“What stood out in our study is that even when amyloid scans appear normal in the clinic, the pTau217 biomarker can identify individuals who later become amyloid-positive,” Yang said. “It also shows that those with low pTau217 levels are likely to stay amyloid-negative for several years.”
The researchers warned that it’s still too early to recommend the blood test as a regular part of screening for seniors.
But it might be a good tool for clinical trials testing new Alzheimer’s drugs by identifying people at higher risk, researchers said.
Eventually, this sort of test could be used for regular health maintenance, the team said.
“As the field is evolving quickly, we’re excited to see discoveries on the research side being rapidly translated to clinical application,” said co-senior author Dr. Jasmeer Chhatwal, a neurologist at Mass General Brigham Neuroscience Institute.
“By anticipating who's going to turn amyloid-positive in the future, we are trying to push back the clock to enable earlier Alzheimer's disease prediction,” he said in a news release.
More information
Stanford Medicine has more on amyloid and tau in Alzheimer’s disease patients.
SOURCE: Mass General Brigham, news release, April 14, 2026
