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

It’s not available yet, but doctors could soon have a new tool to help them diagnose the most common form of dementia


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Danielle Del Plato

A blood test that is being used in research studies but is not yet available in doctors’ offices was found to be highly accurate at detecting two defining characteristics of Alzheimer’s disease, a new study shows.

Health experts say the findings suggest we’re getting closer to having an easier, less expensive way to tell if a patient’s memory and thinking issues are due to Alzheimer’s, the most common form of dementia, which affects an estimated 6.7 million Americans.

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“And that is a revolutionary change,” says Paul Newhouse, M.D., director of the Center for Cognitive Medicine at Vanderbilt University Medical Center and clinical core leader for the Vanderbilt Alzheimer’s Disease Research Center.

What doctors rely on now is a patchwork of physical and cognitive tests and pricey brain scans or invasive spinal taps to make an Alzheimer’s diagnosis. “A blood test would be preferable,” says Ronald Petersen, M.D., director of the Mayo Clinic Alzheimer’s Disease Research Center and the Mayo Clinic Study of Aging.

The latest research, published Jan. 22 in JAMA Neurology, examined the accuracy of a blood test that identifies a specific protein in the blood, called p-tau217, among a population of nearly 800 participants across three study groups. This protein serves as an indicator for the buildup of two substances in the brain that are hallmarks of Alzheimer’s disease: amyloid plaques and tau tangles. 

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.

The benefits of a blood test

This isn’t the only blood test that’s been developed to detect Alzheimer’s, Petersen points out, and others have produced promising results in studies too, so evidence continues to build for their use in clinical settings. “I think this is a step forward; this is important. This is something that the field has been waiting for,” he says.

That’s because 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.

It could also streamline access to Alzheimer’s treatments, like the newly approved medication Leqembi, and help identify patients who are more likely to benefit from it. Leqembi works by clearing amyloid in the brain, so confirmation of amyloid is required before it can be prescribed.

Eventually, blood tests could help primary care physicians identify patients who may have Alzheimer’s disease and direct them to a specialist sooner, explains Maria C. Carrillo, chief science officer for the Alzheimer’s Association. According to a paper published in the journal Alzheimer’s & Dementia, 50 to 70 percent of symptomatic patients who have Alzheimer’s disease are missed or misdiagnosed in the primary care setting.

“I think there’s even another potential implication from blood tests, which is primary screening of individuals who have no symptoms,” Newhouse says. “It could be the case that we are able to use blood tests to predict the likelihood of somebody developing Alzheimer’s disease even years before they develop symptoms,” similar to the way a cholesterol test can help predict your risk of heart disease. Research shows that changes in the brain can start years, decades even, before Alzheimer’s symptoms begin.

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.

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“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.

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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 last summer 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,” the Alzheimer’s Association’s Carrillo says. “And it’s not that far away.”

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