Described by experts as “a big step forward,” “a breakthrough,” and “a real game changer” in the fight against dementia, a simple blood test is now able to diagnose Alzheimer’s disease years before the first symptoms appear.

What’s more, the test is extremely accurate, correctly predicting Alzheimer’s disease in nine out of ten people.

So, how does this blood test work? It detects a protein called p-tau217.

In a healthy brain, tau is a protein that helps structures within nerve cells transport nutrients to keep brain tissue healthy, but in Alzheimer’s, tau loses its shape and collapses into tangles. As a result, nutrient transport ends, brain cells die and memory declines.

If you’ve read much about Alzheimer’s, no doubt you’ve heard of these “tau tangles.”

A build-up of tau in the brain is considered a hallmark of Alzheimer’s disease. In fact, the latest research suggests that tau build-up is a better physical marker of Alzheimer’s disease than the dreaded amyloid plaque.

What About Amyloid Plaque?

While amyloid-beta plaque is a better-known sign of Alzheimer’s disease since it also accumulates in the brain, the research on how these plaques affect memory is conflicting.

For instance, researchers have found a build-up of amyloid-beta plaques in seniors who remain cognitively healthy as well as those who suffer from dementia.

This is one reason researchers are now turning their attention toward tau tangles, and a protein found within them called p-tau217.

Diagnosing Alzheimer’s Disease

Currently, the only way to know for certain that a patient has Alzheimer’s is to examine the brain after death.

Still, doctors rely on positron-emission tomography (PET) scans and cerebrospinal fluid (CSF) tests to detect early changes in the brain that likely indicate the presence of Alzheimer’s disease before giving their diagnosis. Trouble is, these scans are very expensive, and spinal fluid tests are invasive and uncomfortable, so they’re not often used as an early predictor of the disease.

In the search for a cheaper, easier test that can detect Alzheimer’s disease before symptoms appear, scientists turned to the blood.

Researchers from the U.S. and Sweden compared blood measurements of p-tau217 with three other potential early biomarkers of the disease in 1,400 patients with either suspected Alzheimer’s disease, suspected Alzheimer’s disease with a genetic link, or some other neurodegenerative condition.

They analyzed these markers in the blood and spinal fluid, carried out PET scans and then later examined autopsy findings on the patients who had died.

Highly Specific for Alzheimer’s

Researchers found p-tau217 to be a far more accurate predictor of Alzheimer’s disease than any of the other markers. What’s more, the presence of p-tau217 could distinguish patients with Alzheimer’s rather than other forms of dementia with 96 percent accuracy, making it a highly specific test for Alzheimer’s disease.

Even more exciting, researchers found that for those with the genetic form of the disease, levels of the protein were not only raised seven-fold, but started to rise 20 years before the onset of cognitive decline.

This is a remarkable discovery. And it’s made even more remarkable by knowing that these same researchers compared autopsy findings with blood the diseased person donated before they died to ensure the accuracy of their results.

Accurate in Nine Out of Ten Patients

For those who died with plaques and more extensive tau tangles in the brain, the blood test was 98 percent accurate in diagnosing Alzheimer’s. With fewer tau tangles the degree of test result accuracy still remained high, at 89 percent.

This past July, the research teams presented their findings on p-tau217 at the virtual Alzheimer’s Association International Conference.

Professor Clive Ballard, a world-leading expert in dementia from the United Kingdom, commented on the discovery saying, “This research represents an exciting step towards developing a blood test that could help identify Alzheimer’s.

“The findings come from a top research group and this is an encouraging and robust development.”

Almost as Accurate as a PET Scan

Other research groups at the conference confirmed the importance of p-tau217 in diagnosing Alzheimer’s disease.

Using a highly sensitive technique called mass spectrometry, which detects entire molecules of tau or amyloid, researchers from Washington University School of Medicine found that p-tau217 was closely linked to the buildup of amyloid plaques in the brain.

And another group from the University of California San Francisco conducted a study of 617 people, including 119 healthy controls, 74 people with Alzheimer’s and 294 with another form of dementia.

P-tau217 was five-fold higher in the Alzheimer’s patients compared to healthy controls. When compared to patients with another form of dementia, the Alzheimer’s patients had a four-fold higher incidence of p-tau217. In their study, the protein was 96 percent accurate in predicting whether a person had a tau positive PET scan.

“Huge Advance in Alzheimer’s Disease”

Dr. Michael Weiner, an Alzheimer’s disease researcher at the University of California, San Francisco, says, “This blood test very, very accurately predicts who’s got Alzheimer’s disease in their brain, including people who seem to be normal.

“It’s not a cure, it’s not a treatment, but you can’t treat the disease without being able to diagnose it. And accurate, low-cost diagnosis is really exciting, so it’s a breakthrough.”

Rudolph Tanzi, professor of neurology at Harvard University, also enthusiastically declared, “Based on the data, it’s a big step forward. It has the promise to make early detection of the disease possible, before we have symptoms.”

Dr. Howard Fillit, of the Alzheimer’s Drug Discovery Foundation in New York City, believes the test could be “a real game changer. I really think this is going to be a huge advance in Alzheimer’s disease,” he said.

I agree and can’t help but think if people could have knowledge they’re progressing towards Alzheimer’s disease two decades beforehand, they could implement diet and lifestyle changes that might change the course of the disease or even stave it off completely.

This could be a very exciting new field of investigation for natural and alternative therapies for Alzheimer’s disease prevention.

The p-tau217 blood test for early prediction of Alzheimer’s disease could be widely available within the next three years.


  1. https://www.alz.org/aaic/releases_2020/blood-biomarkers-tau.asp
  2. https://www.nytimes.com/2020/07/28/health/alzheimers-blood-test.html?
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