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Can a Blood Test Detect Alzheimer’s Disease?

Memory Expert Zaldy Tan, MD, Talks About New Blood Tests Hitting the Market, What They Measure and Who Should—or Shouldn’t—Take Them

In July, the first direct-to-consumer blood test designed to assess a user’s risk for developing Alzheimer’s disease hit the market. The test, which has not undergone Food and Drug Administration (FDA) review, measures the level of a protein called beta amyloid, a key component of plaques that form in the brains of Alzheimer’s disease patients, disrupting brain function.

Zaldy Tan, MD, MPH

Zaldy Tan, MD, MPH

Zaldy Tan, MD, MPH, medical director of the Jona Goldrich Center for Alzheimer’s and Memory Disorders and the Carmen and Louis Warschaw Endowed Chair in Neurology at Cedars-Sinai, sat down with the Cedars-Sinai Newsroom to answer questions about the test, as well as similar blood tests that are in development.

What do these new blood tests measure?

Blood tests for Alzheimer's disease provide a convenient way for patients to see whether they might be developing Alzheimer's-type changes or pathology in their brain years before memory issues even begin. The challenge here is that these brain changes do not necessarily mean that they have Alzheimer's disease, which is a clinical diagnosis. What blood tests do is to look at traces of certain proteins that are known to develop in patients with Alzheimer's disease.

Who should take this type of blood test?

First, it is important to remember that the test currently on the market has not been evaluated or approved by the FDA. Neither have any of the other, similar tests that are in development. And these blood tests should really be reserved for people who are at risk or are having early symptoms of memory issues. These types of blood tests do not have a place for people who do not have significant risk factors for developing memory problems, or are not having any functional or social issues related to cognitive change.

Does a blood test alone provide enough information to diagnose potential memory issues?

A blood test will not answer that question. Only a trained clinician can. So, for people who are interested in these kinds of blood tests, I would suggest that patients first speak with their healthcare professional to see if these tests are right for them.

Alternatives to these newer-on-the-market tests are things like cognitive testing, a neurologic examination, or consultation with memory specialists. These blood tests provide just one data point or piece of information among many that need to be collected to know if someone is having early signs of Alzheimer's disease.

Do these blood tests help patients qualify for some of the new Alzheimer’s disease treatments such as lecanemab?

Currently, we confirm the presence of amyloid beta in the brain and qualify patients for these treatments through a PET scan of the brain or a lumbar puncture to test cerebrospinal fluid. These blood tests will need to be tested further and will need to be cleared by the FDA to make sure that they are reliable before they can be used to qualify patients for these new treatments. 

What are the risk factors for Alzheimer’s disease?

Age is one of the main risk factors for developing dementia later in life. Others include family history, especially having dementia diagnosed in a first-degree relative. People who have had traumatic brain injury or have had a stroke or have Parkinson's disease or other neurologic conditions may also be at increased risk of developing dementia.

What can people do to reduce their risk of Alzheimer’s disease?

So, what we need to do is to make sure that our brains get the blood supply that they need, and that is best assured by a healthy lifestyle: good diet, good sleep, exercise, increased socialization to make sure those connections between brain cells are nice and healthy. And of course, protecting your brain from trauma by wearing a helmet when you cycle or skate, wearing a seatbelt when you're driving, is important. So, it's really a combination of things in order to reduce the overall risk. Just like we do for our hearts and our bodies, we need to have a multimodal approach to risk reduction of brain disease, including Alzheimer's disease.