New FDA-Approved Biomarker Blood Test Could Advance the Field of Care for Alzheimer’s Disease

The first-of-its-kind blood test for biomarkers of amyloid brain plaque paves the way for less-invasive screening for Alzheimer’s disease. A Keck Medicine of USC physician shares insights.

The U.S. Food and Drug Administration (FDA) recently approved the first-ever blood biomarker test for amyloid plaques in the brain. The Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio tests for the presence of amyloid plaques in patients 55 years and older with existing signs and symptoms of cognitive decline.  

“This test, which captures the presence of amyloid brain plaque, is very good in diagnosing Alzheimer’s disease but not in predicting who gets Alzheimer’s dementia,” he says. Since not all patients with amyloid plaques progress to dementia, this test is best used in patients who show clinical symptoms of dementia to diagnose Alzheimer’s dementia. Doctors still need to be trained to recognize and understand how to make clinical diagnoses of dementia, he stresses. 

Other methods of testing for amyloid plaques through either a PET scan or a cerebrospinal fluid test can be invasive, expensive and cumbersome. By comparison, this newly approved blood test could make screening for amyloid plaque more widely available.  

“This offers patients and families hope that we can be more accurate in our diagnosis and get patients the diagnoses they need for care in a quicker and less-invasive way,” Yassine says. 

Doctors will need to use caution and be trained in clinical diagnoses, he stresses. “We always need to be educated and careful with new tests and medicines for Alzheimer’s, because we do not want to give patients anxiety with either false-positive diagnoses or situations where someone might have abnormal amyloid test but may not progress to dementia,” Yassine says. 

Who needs this test and when? 

Now that this test is approved, the big debate in the field is how early it should be used. Primary care doctors have to fully understand what this new test means and the limitations of the testing, Yassine explains.  

“For example, if you get someone who has no symptoms of memory or cognitive decline asking for the test, getting the test done can lead to a false-positive diagnosis because it’s not good enough to make an Alzheimer’s dementia diagnosis without clinical symptoms,” he says. 

While experts at the USC Center for Personalized Brain Health work with individuals who have the APOE4 gene, who are at higher risk for developing Alzheimer’s disease, Yassine is on the conservative side of determining who should take this test and when.  

“People who have a family history of the gene might get anxious if they get this test — and it’s positive — because we don’t really know exactly what it means yet,” he says. “The evidence suggests we shouldn’t be performing this test on people who don’t have symptoms; amyloid in the brain doesn’t always lead to dementia or Alzheimer’s.”  

One future area of research he does see advancing the field is to take people with a genetic risk or family history of Alzheimer’s disease and to use this test to substratify them as amyloid-positive or amyloid-negative to determine how that affects disease development and progression and the response to certain interventions, such as blood pressure control or lifestyle changes. 

The future of biomarker testing for Alzheimer’s disease 

While some in the neurological disorders field have argued that this test could allow people positive for amyloid plaques in the brain to take preventative treatments to clear them, such as newly approved medicines Kisunla (donanemab) and Leqembi (lecanemab-irmb), Yassine says this hypothesis is unproven and comes with a fair number of risks.  

“It’s dangerous to assume that if you take someone who is asymptomatic and remove amyloid from the brain, you’ll be curing or stopping Alzheimer’s, because there have been no studies that show this,” Yassine says. “It could happen, but no one has proven that’s the case yet. And it’s also likely that giving them one of these treatments could cause severe side effects in the brain such as swelling, headaches and hemorrhages.”  

Another problem with that viewpoint is that there are people who have amyloid in their brains, but no dementia. And sometimes elevated amyloid levels do not come from the brain, he says. Additionally, there are many other factors that play into Alzheimer’s, such as inflammation.  

“I think as the field evolves, we will also need to develop tests for brain inflammation and other aspects of Alzheimer’s dementia,” Yassine says. He relates this to how we treat and care for heart disease. For example, if someone has heart disease, they will often get blood pressure medication, cholesterol medication, blood sugar regulation and many other things. “You don’t just use one drug,” he points out. 

“And Alzheimer’s dementia is as complicated — if not more complicated — than cardiovascular disease, so there’s room to add other treatments on top of anti-amyloid medication to achieve additional clinical efficacy,” Yassine says.  

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