FDA approves new Alzheimer’s blood test for people over 55. Here’s what it can — and can’t — tell
It’s more accessible, for starters.
It used to be that doctors couldn’t diagnose patients with Alzheimer’s disease until after they had died. But new tests have made it possible to figure out what’s driving a person’s cognitive decline while they’re still alive, including a blood test.
Now, the Food and Drug Administration (FDA) has approved another blood test to test for Alzheimer’s disease.
It’s called Elecsys pTau217, and it’s a blood biomarker test that can help doctors ID patients in primary care and specialty care who are unlikely or likely to have Alzheimer’s-related brain changes. That means your primary care physician could order this test, along with neurologists, making it accessible to more healthcare providers.
While that sounds good in theory, doctors say there are pros and cons to this level of accessibility. Here’s why.
What is the new Alzheimer’s blood test?
Elecsys pTau217 is a blood test from Roche that can be used to rule in or rule out the presence of amyloid plaques, which are hallmarks of Alzheimer’s disease, per a press release from Roche. The test is designed for people aged 55 and up who have signs, symptoms, or complaints of cognitive decline.
The test results are designed to be used “in conjunction with clinical information and other relevant findings” to help diagnose or rule out Alzheimer’s disease in patients, according to Roche.
“Currently, many patients face prolonged uncertainty because traditional dementia diagnostics like brain scans and spinal taps are prohibitively expensive, physically invasive, and restricted to specialized medical centers,” says Manisha Parulekar, division chief of geriatrics and co-director of the Center for Memory Loss and Brain Health at Hackensack Meridian Health. “Blood biomarkers offer a transformative alternative.”
These tests are usually accessible, affordable, and accurate, and can give patients and their families answers without pain or high costs. (Roche hasn’t yet publicly revealed how much the test will cost.)
“This breakthrough allows families to find direction, reducing the anxiety of the unknown so that targeted care can begin,” Parulekar says.
How is it different from the existing Alzheimer’s blood test?
There is already a blood test for Alzheimer’s disease available, called Lumipulse. But the test requires visiting a specialty lab and is a little more complicated than the latest offering.
“Blood tests for Alzheimer’s already exist, but many combine multiple measurements—for example, pTau217 with amyloid-beta — and interpret them as a ratio,” explains Davide Cappon, director of neuropsychology at Tufts Medical Center. “This measures pTau217 alone.”
In practical terms, a low result means amyloid in the brain is unlikely, while a high result makes it much more likely, he explains. “Importantly, [the test is] just ruling in or out related brain pathology, not making a diagnosis based on a blood test alone,” Cappon says.
Because it’s designed to run on widely available lab instruments, clinics and hospitals can use their existing diagnostic tools, she points out. That makes accurate Alzheimer’s assessments accessible, even in primary care settings, Parulekar says.
But Clifford Segil, a neurologist at Providence Saint John’s Health Center in Santa Monica, California, has concerns about anyone being able to order this test.
“This is quite scary, as the doctor ordering a test should know how to interpret a positive or negative result,” he says.
Segil points out that the value of blood tests to determine Alzheimer’s disease “remains debatable” with neurologists, given that the disease can be complicated to diagnose.
“Primary care doctors who obtain this test will not know how to counsel patients on the meaning of a positive or negative result,” Segil says.
Who is a candidate for this blood test?
Anyone over the age of 55 with signs and symptoms of Alzheimer’s disease can receive the test.
“The biology of Alzheimer’s can start years before symptoms, so yes, a blood biomarker can become abnormal before someone develops obvious memory problems,” Cappon says. “But that does not mean we should test everyone who feels well. This test is intended for people who already have cognitive symptoms or concerns.”
Cappon points out that more people without symptoms are asking for these tests.
“If someone is cognitively normal and the biomarker comes back positive, we cannot yet tell them with certainty whether they will develop symptoms—or when,” he says. “So in someone without cognitive concerns, I think we still need to be very thoughtful about what question we are trying to answer and what we would actually do with the result.”
Do you still need to have symptoms to be diagnosed?
Yes, you still need to have symptoms like memory loss.
“The pTau217 test is not a screening tool for healthy individuals; it requires clinical context,” Parulekar says. “When people experience cognitive decline and report complaints, doctors can use this blood test to supplement their evidence.”
Even if the biomarker test is positive, your doctor will still need to incorporate their evaluation into the diagnosis.
“A definitive Alzheimer’s diagnosis will always incorporate a doctor’s evaluation of the patient’s actual, observable symptoms alongside the lab results,” Parulekar says.