Healthy Mind

This New Blood Test Could Identify Alzheimer’s Disease Decades Before Symptoms Appear

Emily Laurence

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One of the major roadblocks related to treatment for Alzheimer’s disease—the most common form of dementia that is affecting 5.8 million people in the U.S.—is that early diagnosis has been impossible. In fact, a true Alzheimer’s diagnosis isn’t possible until after death, after brain tissue can be examined in an autopsy. Thus, doctors diagnose the disease through a series of cognitive tests, brain imaging scans, and bloodwork to help them rule out other conditions and make an educated guess. Sometimes it can take six to 12 months to confirm the diagnosis; some people have to wait years before getting one.

That frustrating process may change soon with a ground-breaking new blood test, which was the focus of a study published in JAMA at the end of July. The test identifies the protein ptau-2017, a biomarker for Alzheimer’s, and was able to better predict the disease than several other existing biomarkers we currently test for. “As reported at the Alzheimer’s Association International Conference 2020, levels of ptau-217 measured in blood may be the most specific biological marker to give evidence that a person has Alzheimer’s, and the earliest marker, among those tested to date, to show measurable changes in the brain, possibly even decades before symptoms occur,” says Keith Fargo, PhD, the director of scientific programs and outreach at the Alzheimer’s Association.

Again, ptau-217 isn’t the only known biomarker for Alzheimer’s. But Jessica Caldwell, PhD, the director of the Women’s Alzheimer’s Movement Prevention Center at the Cleveland Clinic in Las Vegas, says it’s an important discovery because of how accurate it’s proving to be. “There are many different Alzheimer’s disease biomarkers, with some relatively easier and cheaper to measure—like a brain MRI—and others very difficult or expensive—such as a spinal tap or brain amyloid scan,” she says. “However, having a single biomarker does not definitively diagnose Alzheimer’s in someone with dementia or at risk. This test is predicting which people have Alzheimer’s dementia at 96 percent accuracy, and also predicts who has brain amyloid among people who have no memory problems at 90 percent accuracy. This is really remarkable!” Basically, it not only can predict the disease with someone already experiencing dementia, it can also predict the presence of the brain plaque buildup years before someone starts having memory problems.

“This test is predicting which people have Alzheimer’s dementia at 96 percent accuracy, and also predicts who has brain amyloid among people who have no memory problems at 90 percent accuracy. This is really remarkable!” — Jessica Caldwell, PhD

She says the blood test is particularly encouraging for women, who are at a greater risk for Alzheimer’s disease than men. “Women are often diagnosed too late with Alzheimer’s, in part because memory tests are not sensitive enough for us,” she says. “Here, as simple blood test could be paired with memory testing to give a fuller picture of risk. That could be really helpful for targeting who is most in need of prevention services or treatment and support.”

While Alzheimer’s disease is a progressive disease with no cure, both experts say getting the blood test could lead to earlier and better interventions, which would lessen the severity of the symptoms. “There’s a direct connection between having good diagnostic tools—especially for early detection—and the ability to develop treatments,” Dr. Fargo says.

However, Dr. Fargo adds that the test still in the early phases and is not yet available in clinical settings. He says it still needs to be tested in long-term, clinical studies to prove its efficacy. Thus, it’s not yet known how expensive the test will be or if it will be covered by insurance. “In the meantime, if you have known biomarkers for Alzheimer’s or are worried about your memory, good steps to take are seeing a neurologist or neuropsychologist with expertise in memory problems and dementia who can give you an assessment of your current difficulties and a plan,” Dr. Caldwell says.

Even though the test isn’t available to the public yet, it’s a big step forward for the Alzheimer’s prevention field. “This test is a great example of how we are getting closer to having quick tests that can give us better answers about whether we are at risk or what type of brain change we are experiencing,” Dr. Caldwell. And it’s getting scientists closer to the ultimate goal: a cure.

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