You probably have seen reporting on a new Alzheimer’s blood test recently approved by the U.S. Food & Drug Administration (FDA). The approval provides clinicians with an accessible and relatively inexpensive Alzheimer’s test, but will it be available to all older adults who fear age-related cognitive impairment?
No, says Mount Sinai neurologist Samuel Gandy, MD, PhD. “This definitely isn’t a screening tool you should expect to be able to get access to in the absence of noticeable memory issues,” he says. “It also isn’t designed to be a standalone test—it must be coupled with other diagnostic methods and interpreted in the context of each individual patient.”
How the Alzheimer’s Blood Test Works
The new Alzheimer’s test—called the Lumipulse G pTau 217/ß-Amyloid 1-42 Plasma Ratio—works by measuring blood plasma levels of two abnormal proteins: amyloid-beta (A-beta) and tau. Both can build up in the brain in older age, and these deposits are believed to contribute to Alzheimer’s disease.
The blood test results come back as a ratio that can be used to predict how much amyloid is present in the brain. The study that formed the basis of the FDA approval included 499 cognitively impaired people and compared the blood test with positron emission tomography (PET) scans and cerebrospinal fluid (CSF) samples. More than 90 percent of participants who had a positive blood test result were found to have amyloid plaques by PET scan or CSF test result.
How Is Alzheimer’s Diagnosed?
Up until now, PET scans and CSF testing have been the standard advanced testing methods for Alzheimer’s disease. Both are considered invasive—PET scans require the use of an injected radioactive substance, and CSF samples are obtained through a lumbar puncture (often referred to as a spinal tap).
These tests also are expensive and may not be accessible to people who live long distances from specialized medical facilities. The new Alzheimer’s blood test would be easier to obtain, more affordable, and less invasive.
Not for Broad Use
A-beta and tau begin to build up in the brain decades before early signs of Alzheimer’s arise, according to Dr. Gandy.
“Some experts posit that Alzheimer’s drugs might be more beneficial if they could be given before significant cognitive deterioration sets in, but that possibility is still being researched,” he says.
This means that you won’t be able to get the new Alzheimer’s blood test alongside the routine blood tests you undergo for your annual physical—and Dr. Gandy says there are good reasons for caution and careful targeting of the new test. “The best current use of the test is to determine who might be a candidate for an amyloid PET scan,” he explains. “It is possible that the blood test might one day replace the amyloid PET, but that is not the case today.”
Who Is Eligible?
The Alzheimer’s test is intended to be used in people ages 55 and older who have clear early signs of Alzheimer’s disease. What might those symptoms be?
“Look out for a pattern of consistent problems with your memory,” Dr. Gandy says. “Examples include forgetting things you normally wouldn’t, being confused by routine tasks, getting lost in familiar surroundings, being unable to follow and take part in conversations, and becoming overwhelmed by relatively simple decisions.”
If you’re having symptoms like these, your primary-care physician (PCP) might order blood tests to rule out medical causes for your memory issues (like vitamin deficiencies or hypothyroidism). If those tests are unrevealing, then more advanced or specific tests may be required (for example, brain imaging). These tests can be ordered by your PCP, or they might instead refer you to a specialist provider. If your provider believes that Alzheimer’s disease is a possible or likely explanation for your symptoms, then you and they should together determine the best path forward to rule Alzheimer’s in or out.
Collaborative Decision-Making is Vital
The approach to Alzheimer’s today is complex and in transition, and Dr. Gandy emphasizes that there is no one-size-fits-all pathway.
“My advice is for physicians and patients is to collaborate on decision-making,” he says. “Some physicians offer amyloid-targeted therapies to qualified Alzheimer’s patients, and the earlier those are considered the better. People with mild symptoms who are not on blood thinners might be interested in taking that route. The most important consideration is to determine whether there is brain amyloid or not, and this is where amyloid PET and blood tests fit in. If there is no amyloid, then the new anti-amyloid drugs should not be used—but there is still a place for standard symptomatic treatments.” The latter include donepezil (Aricept), galantamine (Razadyne), or rivastigmine (Exelon).
Dr. Gandy adds that when you and your provider discuss whether an amyloid test is right for you, it is important to realize that the blood test is currently not reimbursed and that if you are not yet retired, a positive test in your medical record could have implications for employability and insurability. He notes that this problem arose during the 1990s, when the APOE test (which checks for a genetic mutation that raises the risk of Alzheimer’s disease) became available.
“We are fortunate to be living in a time when progress is finally being made in treating Alzheimer’s, but ethical use of test results cannot be guaranteed as of this writing,” he observes. “This is why I advise early and collaborative decision-making involving providers, patients, and often family members or caregivers.”
