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November 18, 2022

Can a simple blood test detect Alzheimer's disease?

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    New blood tests that can detect abnormal proteins associated with Alzheimer's may change the way the disease is diagnosed, allowing many patients to be tested before they even show symptoms, Laurie McGinley reports for the Washington Post. However, despite the potential benefit of these tests, some health experts caution that more research is needed before they can be used more broadly.

    Could new blood tests help improve Alzheimer's diagnoses?

    According to the Alzheimer's Association, almost 13 million Americans are expected to develop Alzheimer's by 2050 and research suggests that this number will grow to 153 million people worldwide.

    However, diagnosing Alzheimer's, especially during its early stages, can be difficult. Currently, spinal taps and specialized PET scans can accurately detect biological changes or biomarkers present in the disease, but spinal taps are invasive and the scans, which can cost $5,000 or more, are not currently covered by Medicare except for in clinical trials.

    Typically, physicians will rely on symptoms, cognitive tests, and other assessments to diagnose Alzheimer's, but research shows that more than half of patients who are evaluated for the disease in primary care are misdiagnosed.

    To potentially make diagnosing Alzheimer's easier while still preserving the accuracy of more specialized tests, several companies have developed blood tests for the disease. So far, three tests by C2N Diagnostics, Quest Diagnostics, and Quanterix are available on the market, and several others are being developed and tested in trials.

    According to McGinley, these tests "detect tiny amounts of abnormal proteins in the blood, including a sticky version called amyloid beta, to determine whether the pathological hallmarks of Alzheimer's are present in the brain."

    Because brain abnormalities can develop 10 to 20 years before symptoms emerge, the blood tests may alert people to their potential risk of Alzheimer's much earlier. This would allow them to make lifestyle changes to improve their health or receive a preventive therapy if one is ever developed.

    So far, early data on these tests suggests that their accuracy is similar to that of spinal taps or PET scans. For example, results from C2N's PrecivityAD test, which is targeted at patients ages 60 and older experiencing memory problems, agree with PET scans roughly 85% of the time.

    Some companies are also already working on next-generation tests, which can detect other proteins such as tau that have been associated with Alzheimer's. Currently, C2N is close to launching a combination amyloid-tau test, which is 90% accurate. Similarly, Eli Lilly has developed its own test to detect tau and expects to launch it commercially next year.

    "If you had asked me five years ago if we would have a blood test that could reliably detect plaques and tangles in the brain, I would have said it was unlikely," said Gil Rabinovici, a neurologist at the University of California, San Francisco. "I am glad I was wrong about that."

    How useful will these blood tests be?

    So far, these Alzheimer's blood tests have seen limited use among patients outside of clinical trials. Although physicians can prescribe the tests for their regular patients, it is uncommon since they can be expensive and are often not covered by insurance.

    However, many health experts say it's only a matter of time before these blood tests are adopted more widely, especially if federal regulators approve new Alzheimer's treatments.

    For example, Eisai and Biogen in September released data showing that its experimental Alzheimer's drug lecanemab slowed cognitive and functional decline by 27% compared to a placebo. According to McGinley, lecanemab "was the first Alzheimer's drug to clearly slow deterioration in a well-executed trial."

    Currently, the data on lecanemab has not been peer-reviewed, but more information is expected later this month. FDA is also scheduled to decide whether to approve the drug by Jan. 6.

    If more Alzheimer's treatments are approved, demand for the blood tests will likely increase as well since physicians will need to know whether patients have a buildup of abnormal proteins in their brains first before prescribing any treatment targeting them.

    "If there is a therapy that clearly demonstrates a clinical benefit, demand for these blood tests could skyrocket," said Reisa Sperling, director of the Center for Alzheimer Research and Treatment at Brigham and Women's Hospital.

    Although some experts believe that the blood tests can be used in primary care settings now, others have recommended a more cautious approach, saying that more research is needed before the tests can be used broadly.

    Last year, physicians and researchers convened by the Alzheimer's Association published an article with recommendations on how the blood tests should be used. While the authors said the tests could be used by memory clinics alongside other confirmatory measures, they recommended against their use by primary care doctors.

    "We believe additional research is needed before they could be used as stand-alone diagnostic tests broadly in primary care," said Rebecca Edelmayer, senior director for scientific engagement for the Alzheimer's Association and a co-author of the paper. Some research recommendations include studying the tests in more diverse populations and in patients with medical conditions, such as chronic kidney disease, that could affect the results.

    "This is a brand-new technology, and it will take some time to figure out how useful it really is, in what types of patients and under what kind of circumstances," said Jonathan Drake, associate director of the Alzheimer's Disease and Memory Disorders Center at Lifespan's Rhode Island Hospital. (McGinley, Washington Post, 11/17)

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