A Simple Blood Test for Alzheimer’s? ‘It’s Not That Far Away’

Doctors could soon have a new tool to help them diagnose the most common form of dementia

Rachel Nania,

AARP

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En español

Published January 25, 2024

/ Updated July 29, 2024

graphic of a brain surrounded by red blood cells

Danielle Del Plato

A new study adds to a growing sense of optimism that doctors could soon have a faster, simpler and more affordable way to tell if a patient’s symptoms of memory loss and confusion are caused by Alzheimer’s disease, the most common form of dementia that affects nearly 7 million older Americans.

A team of researchers based in Sweden found that a blood test was about 90 percent accurate in diagnosing Alzheimer’s disease in people experiencing thinking and memory problems. In the research study, primary care physicians were 63 percent accurate in an Alzheimer’s diagnosis when not using the blood test; specialists were 73 percent accurate when not using the test, which identifies a specific protein in the blood that serves as an indicator for the buildup of amyloid plaques and tau tangles, two defining characteristics of Alzheimer’s disease.

The study was presented at the 2024 Alzheimer’s Association International Conference and published in the medical journal JAMA.

This blood test and others like it are not widely available to patients outside of research studies, but they could be soon, and that would be a “revolutionary change,” says Paul Newhouse, M.D., director of the Center for Cognitive Medicine at Vanderbilt University Medical Center and clinical core director for the Vanderbilt Alzheimer’s Disease Research Center.

What doctors rely on now when making an Alzheimer’s diagnosis is a patchwork of physical and cognitive tests and pricey brain scans or invasive spinal taps. With more studies like this latest one, blood tests could “serve as the first line of defense in diagnosing the disease,” Howard Fillit, M.D., cofounder and chief science officer of the Alzheimer’s Drug Discovery Foundation, said in a statement.

A study published earlier this year in JAMA Neurology examined the accuracy of a blood test that identifies the same protein in the blood, called p-tau217. The research team found that the blood test was more than 90 percent accurate and was on par with the gold-standard diagnostic tools — positron emission tomography (PET) imaging and cerebrospinal fluid collected from a lumbar puncture — in detecting the brain changes associated with Alzheimer’s disease.

Previous studies have produced promising results, too, so evidence continues to build for the use of blood tests in clinical settings, says Ronald Petersen, M.D., director of the Mayo Clinic Alzheimer’s Disease Research Center and the Mayo Clinic Study of Aging.

“I think this is a step forward; this is important. This is something that the field has been waiting for,” Petersen told AARP.

What are the benefits of a blood test?

For starters, a highly predictive blood test could save a lot of time and money when it comes to making an Alzheimer’s diagnosis, Newhouse says. PET scans and spinal taps can cost thousands of dollars and are performed only in hospitals or specialty clinics.

A faster diagnosis could impact access to new Alzheimer’s treatments that are approved for patients in the early to mild stages of the disease. Research presented at the Alzheimer’s Association’s 2024 conference suggests that the wait time for these treatments could be slashed by several years with an accurate and reliable blood test.

“Currently, eligible patients are falling outside of the treatment window because it takes so long to receive a diagnosis. An easy-to-use blood test could help address that problem,” researcher Soeren Mattke, M.D., director of the Brain Health Observatory at the University of Southern California, Los Angeles, said in a news release issued by the conference.

Another potential implication: Screening individuals for Alzheimer’s disease, even if they don’t have symptoms. Research shows that Alzheimer’s changes in the brain can start years, sometimes decades, before symptoms begin. Enrolling people in clinical trials who are in the earliest stages of Alzheimer’s could help identify treatments that get to work before life-changing symptoms take hold.

How long before blood tests are widely available?

It’s hard to say with certainty, but Babak Tousi, M.D., head of the Clinical Trials Program at the Cleveland Clinic Lou Ruvo Center for Brain Health, predicts blood tests for Alzheimer’s disease will be widely available in the next few years — possibly sooner.

“Widely” is the key word here. There are already commercially available blood tests doctors and researchers can use to assist in making an Alzheimer’s diagnosis. But so far none have been approved by the Food and Drug Administration (FDA), and insurance coverage is lacking, so they’re not commonly used in clinical settings.

The FDA’s approval is not required for laboratory-developed tests, like these blood tests, but many dementia experts say it’s needed to confirm their accuracy and reliability in a patient population, and therefore to boost their widespread use.

Once a blood test is FDA-approved and accepted as an alternative to PET scans and lumbar punctures for an Alzheimer’s diagnosis — and insurers agree to reimburse the cost — we’ll see its full potential to impact Alzheimer’s care, says Anna Nordvig, M.D., a neurologist who specializes in cognitive disorders of the brain at Weill Cornell Medicine in New York City.

The Alzheimer’s Association has also said it is working on guidelines for the use of blood tests.

Concerns about your memory? Talk to your doctor

It’s not just clinicians and researchers who can order an Alzheimer’s blood test. The first direct-to-consumer blood test designed to assess a person’s risk for Alzheimer’s hit the market in 2023 without FDA approval — and more could follow. But when it comes to these products, the advice from many dementia experts is cautionary.

For one, the results won’t reveal whether you have Alzheimer’s disease; they’ll tell you whether amyloid is present in your blood plasma, explains Zaldy Tan, M.D., medical director of the Jona Goldrich Center for Alzheimer’s and Memory Disorders at Cedars-Sinai in Los Angeles.

The problem with that, he says, is some people test positive for amyloid but never go on to develop the symptoms of Alzheimer’s disease.

“My worry with direct-to-consumer is that people might make life decisions or other important decisions based on one blood test, which may not mean what they think it means,” Tan says. “I liken it to getting a cholesterol level. Getting a cholesterol level doesn’t mean that you are going to have a heart attack tomorrow.”

A recent poll from the University of Michigan supports this concern. Researchers found that a significant share of older adults (74 percent) said a positive result from an Alzheimer’s blood test would make them believe they were likely to develop Alzheimer’s disease; nearly two in three adults (64 percent) said such a result would likely cause them significant distress. And nearly 80 percent of those surveyed said they would consider changes to their financial or advance care planning if a blood test result came back positive.

“[Patients] need someone to put results in context,” Tan says.

If you have concerns about your risk for Alzheimer’s, talk to a doctor — you can start with your primary care physician. There are things you can do that may help lower your risk, such as manage high blood pressure and treat hearing loss.

Another reason to speak with your doctor: If you’re experiencing memory loss symptoms, it could be due to another medical condition, including other forms of dementia. “Not all forgetfulness is Alzheimer’s disease,” Petersen says.

Side effects from medications can mimic symptoms of dementia — so can common infections, depression, sleep issues, even a vitamin deficiency. Your doctor can help rule out these other potential causes first and, if needed, refer you to a specialist for further evaluation — possibly even a blood draw in the near future.

“There’s no doubt that there is an absolute urgency, and everybody recognizes that [a blood test] is the Holy Grail,” says Maria Carrillo, Alzheimer’s Association chief science officer and medical affairs lead. “And it’s not that far away.”

Editor’s note: This story, first published Jan. 25, 2024, has been updated to reflect new research.

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