FDA Approves First Blood Test for Alzheimer’s Disease
Diagnosing Alzheimer’s disease has been a complicated process that involves a clinical evaluation from a neurologist and either brain imaging tests or a spinal tap.
The imaging test most often used is a specific positron emission tomography (PET) scan, which shows the presence of amyloid plaques—a hallmark of Alzheimer’s—in the brain. It is costly and not universally available, while a spinal tap (lumbar puncture) is invasive and involves a needle inserted into the lower spine to collect cerebrospinal fluid to look for certain proteins that could signal Alzheimer’s.
But now doctors have a new tool: an Alzheimer’s blood test. The Food and Drug Administration recently approved the first test that uses a blood sample to help diagnose Alzheimer’s disease. The disease, which causes a decline in memory and thinking skills, affects nearly 7 million Americans—and is projected to become more prevalent.
The test, called Lumipulse and made by Japan-based Fujirebio Diagnostics, is for adults 55 and older who show signs of Alzheimer’s disease, the most common form of dementia (a broad term used to describe a decline in cognitive abilities). It is not intended to be a general screening test for people who are asymptomatic, and it is not designed to diagnose other types of dementia, such as vascular dementia, Lewy body dementia, and frontotemporal dementia.
The blood test’s convenience will allow providers to diagnose Alzheimer’s sooner, which is important because the only approved medications for Alzheimer’s disease—Leqembi and Kisunla—are geared toward slowing progression of the condition in its early stages.
“This is great news, and when it’s fully implemented, it will be a game changer in some ways,” says Sayed Azizi, MD, PhD, Yale Medicine’s clinical chief of neurodegenerative disorders. “But there are many nuances to consider.”
The test, Dr. Azizi says, fits into a larger diagnostic process and only makes sense to do after a doctor has determined that a person has memory or cognitive problems. The first step, always, is a clinical evaluation in which your symptoms and medical history are considered.
“If a patient comes to a physician with memory complaints, we offer a clinical evaluation to assess and perhaps quantify the cognitive problem,” says Dr. Azizi, adding that conditions such as diabetes, hypertension, and depression can cause memory and cognitive issues.
The Alzheimer’s blood test, Dr. Azizi explains, can help determine whether Alzheimer’s disease is the cause of the symptoms. “When it comes to dementia, 60% to 70% of cases are caused by Alzheimer’s, and the other 30% to 40% can be a sundry of different things,” Dr. Azizi says. “Because Alzheimer's is the largest percentage, we concentrate on it and want to diagnose it so that we can treat it.”
What does the blood test measure and how accurate is it?
Medical experts do not fully understand all the causes of Alzheimer’s disease. Genetic, biological, environmental, and lifestyle factors all appear to play roles. But researchers have identified certain markers of the disease—including amyloid plaques and tau protein tangles.
Amyloid plaques are clumps of beta-amyloid protein that accumulate between nerve cells (neurons) and are toxic to neurons. Tau is a protein found inside neurons. An abnormal version of this protein is a marker of neuron injury. In Alzheimer’s, these proteins interfere with cell function and can lead to cell death. This process can impair your memory, ability to communicate, and other cognitive functions.
The new blood test measures two proteins (pTau217 and beta-amyloid 1-42) found in plasma, a blood component. It calculates the ratio of the levels to correlate to the presence or absence of amyloid plaques in the brain.
Amyloid plaques, Dr. Azizi explains, can be understood through a simple analogy. “Think of the brain as an engine and the engine gets rusty over time. We all get a little bit of rust, but some people get a little bit more and a little bit earlier,” he says. “And if you get rust in an engine, its wheels don't turn very well. Plaque is like rust, and in some people, it causes memory and cognition problems.”
According to a clinical study, 92% of people with positive results from the Lumipulse test have the presence of amyloid plaques confirmed by either a spinal tap or a PET scan, and 97% of people with negative blood-test results have confirmed negative results from those two other tests.
Dr. Azizi notes that the test is not a definitive diagnosis. There must also be cognitive symptoms as someone can have amyloid plaques and/or tau protein tangles but not be showing symptoms of the disease.
How can someone get this blood test for Alzheimer’s?
If you’re concerned about your memory, the first step should be to see your primary care physician, Dr. Azizi says.
“Primary care physicians can address any other health issues that are affecting memory and cognition. Plus, they have tools at their disposal to screen patients. For example the Mini-Mental State Examination, which asks people to remember a series of words, draw a clock, and recall current events, takes about five minutes," he says.
There's also the Montreal Cognitive Assessment, Dr. Azizi adds, which includes tasks that assess higher-level language skills.
If needed, primary care physicians will refer patients to a memory care clinic to meet with a neurologist or geriatrician specializing in cognitive disorders. At this juncture, based on further assessment, the neurologist would be the one to order further testing.
The new Alzheimer’s blood test is expected to become available in laboratories starting in June and will require a physician’s order. Dr. Azizi says that he expects it be covered by insurance plans, including Medicare.
