Amyloid plaques (shown in orange) are a key feature of Alzheimer's disease in the brain. A new blood test looks for traces of these plaques in the blood. (Image credit: KATERYNA KON/SCIENCE PHOTO LIBRARY via Getty Images)
The U.S. Food and Drug Administration (FDA) recently approved a blood test that finds signs of Alzheimer's disease in the brain, as shown by numerous studies. It is the first blood test in the world available for this common form of dementia.
Let's take a look at how the new blood test works and what its potential benefits are for patients.
Why is a blood test for Alzheimer's disease necessary?
Alzheimer's disease is rapidly increasing, in part because the age group most at risk for dementia is growing. In the United States, 7.2 million Americans aged 65 and older are projected to be living with Alzheimer's dementia in 2025. The proportion of people affected increases with age: About 5% of people aged 65 to 74 have Alzheimer's disease, compared with more than 33% of people aged 85 and older.
Once a doctor confirms that a patient has cognitive decline, blood tests may be used instead of traditional tests to determine the likelihood of Alzheimer's disease. Previously, the gold standard tests for diagnosing Alzheimer's disease were more invasive and expensive, including positron emission tomography (PET) scans, which use radioactive substances, and lumbar punctures (also known as spinal taps), where a doctor uses a needle to obtain a sample of spinal fluid from the lower back. Doctors also sometimes use MRI or CT scans to rule out other causes of cognitive decline.
The new test analyses the ratio of two proteins in a patient's blood, and that ratio is linked to the presence or absence of amyloid plaques, the main hallmark of Alzheimer's disease, found in the brain.
For people experiencing memory problems that may be due to Alzheimer's disease, the first step is to contact their primary care physician (PCP), who should conduct a cognitive test. If signs of cognitive impairment are noted, the patient will be referred to a neurologist for a more in-depth evaluation.
Both dementia specialists and primary care physicians will be able to order the blood test to help with diagnosis, says Dr. Gregg Day, a neurologist at the Mayo Clinic in Jacksonville, Florida; Day led a study of the blood test published in June in the Journal of the Alzheimer's Association. The 2024 study in JAMA found that whether the primary care physician or specialist ordered the test, it was equally accurate in confirming suspected Alzheimer's diagnoses.
Primary care physicians can use the test results to decide whether to refer patients to a specialist who can prescribe treatments such as lecanemab or donanemab, Day says. Or the primary care physician can prescribe drugs such as donepezil, which may help improve cognitive function in Alzheimer's disease. With the FDA's approval, it's expected that Medicare and private insurers will begin covering the new blood test, Day adds.
Who should get a blood test?
The test, called the Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio, is for people 55 and older who have signs and symptoms of cognitive decline confirmed by a doctor. The test is designed to detect amyloid plaques associated with Alzheimer's disease early. (Amyloid plaques are unusual clumps found between brain cells and made up of a type of protein known as beta-amyloid.)
Early detection is important, says Dr. Sayyad Awsim Azizi, clinical director of behavioral neuroscience and memory disorders at the Yale School of Medicine. That's because the Alzheimer's brain is like a rusty engine — a buildup of rust-like plaque that gets stuck on the engine, preventing the wheels from turning, he explains.
Sourse: www.livescience.com
