Blood Tests For Alzheimer’s: Diagnostic Help Comes With New Questions Too (Podcast)

Biomarker blood tests for Alzheimer’s disease are advancing diagnosis and patient care by facilitating earlier disease confirmation, but their advent raises new questions for clinicians to grapple with.

“The new tests are great tools that, when used in the right context, can help narrow down the possibilities when a patient starts showing signs of cognitive decline, but they are not yet at a point to make a definitive diagnosis,” says Jagan Pillai, MD, PhD, a behavioral neurologist with Cleveland Clinic Lou Ruvo Center for Brain Health. “For instance, before a patient can start the treatments that are now available to remove amyloid plaques, they still need an amyloid PET scan or cerebrospinal fluid evaluation to confirm what their blood test shows.”

In the latest episode of Cleveland Clinic’s Neuro Pathways podcast, Dr. Pillai addresses this and other ways in which the new blood tests are reshaping Alzheimer’s disease evaluation and diagnosis. Among the issues discussed:

• The role of amyloid plaques and tau tangles in Alzheimer’s disease
• Diagnostic methods that have preceded blood tests, and their role vis-à-vis blood testing
• Essentials of the FDA-approved blood tests and how they work
• Appropriate use of the blood tests and interpretation of their results
• Test sensitivity and specificity, and how they may translate to real-world use
• Likely new developments in Alzheimer’s blood tests over the next few years

Click the podcast player above to listen to the 26-minute episode now or read on for an edited excerpt of its transcript. Check out more Neuro Pathways episodes at clevelandclinic.org/neuropodcast or wherever you get your podcasts.

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Excerpt from the podcast

Dr. Stevens:I know these blood tests have been available for a very short time, but how do you see them affecting your practice?

Dr. Pillai: There are two main ways. One is that there are a lot of conversations about this. People are excited and want to get a cognitive assessment now because it’s in the front of their mind. We’re getting a lot more demand for assessments from people wanting to see if they can get a blood test, as the tests are for people who have clearly documented cognitive impairment.

The second effect is that people who should not be getting these tests are also trying to get them. These are people who are completely normal but who may have a family history of Alzheimer’s disease or are just anxious and want a test. They may manage to get one even though it’s not appropriate for them, and then if they get a false-positive result they may struggle with what that means for them.

Dr. Stevens:In the case of a positive blood test in someone who’s asymptomatic, is there any sense of how many years it might take for the disease to manifest?

Dr. Pillai: Alzheimer’s disease is a slow process that happens in the body over a period of time. The estimate now is that some of the changes may be going on for 15 or 20 years before a person has clinical symptoms. So there is this phase called preclinical Alzheimer’s disease where a person is completely normal cognitively. If such a person were to do these blood tests, the result would show up as positive. But we don’t know if that person will develop symptoms or may not develop symptoms. And if they do develop symptoms, we don’t know if it will be in the next five, 10 or 15 years. So the question is, what are you going to do with a positive test in this population? That's why there’s a need to only do testing when there’s clearly documented cognitive impairment.