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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.
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