A new blood test appears to be highly accurate when screening for Alzheimer’s disease, even before symptoms occur, and experts say it’s a promising step forward.
A new blood test that looks for a key biomarker of Alzheimer’s disease, a protein called phosphorylated tau or p-tau2, showed “high accuracy” in a new study — meaning it could soon be a more accessible, affordable way to diagnose the disease.
The study found that the blood test was up to 96% accurate in identifying elevated levels of beta-amyloid (another hallmark of Alzheimer’s) and up to 97% accurate in identifying tau. The research was led by Nicholas Ashton, Ph.D., a professor of neurochemistry at the University of Gothenburg in Sweden, and published in JAMA Neurology on Monday.
“If we could easily biopsy the brain, we could look under the microscope and see accumulations of misfolded proteins inside and surrounding nerve cells,” says Dr. Alison Reiss, M.D., an associate professor at the NYU Long Island School of Medicine and a member of the Alzheimer’s Foundation of America’s (AFA) Medical, Scientific and Memory Screening Advisory Board.
“This would give us the diagnosis just in the same way that we can see lung or breast or skin cancer under a microscope. However, since we can’t take out a piece of brain to examine, we have to find other ways to diagnose Alzheimer’s disease," says Reiss to Healthnews.
Breaking down different Alzheimer's tests
Alzheimer’s can currently be diagnosed using PET scans, which show decreased glucose metabolism in specific brain areas that indicate Alzheimer’s disease, but Reiss says these are very expensive and require an intravenous injection. The disease can also be diagnosed using cerebrospinal fluid (CSF) taken by spinal tap, which is then examined for amyloid-beta and/or tau, though this is an invasive procedure.
Quest Diagnostics did release a blood test that assesses beta-amyloid levels last year, though the company says it is only meant to help assess someone’s risk of developing the disease, and Reiss says it is “not as accurate” as the CSF test.
“The blood tests of tau are a breakthrough,” Reiss says. “Dr. Ashton and his group have found that a detection system for phosphorylated Tau 217 in the blood is excellent at identifying persons at-risk for Alzheimer’s disease and is as good as PET scans or CSF amyloid without the disadvantages of expense or invasiveness.”
The test, called the ALZpath pTau217 assay, is commercially made and easily accessible. While it is only currently available for research, it is expected to be available to the public soon. The test, according to Reiss, is “non-invasive, easier to perform, less costly, and can be done right in the doctor’s office.”
The importance of early Alzheimer's diagnosis
There is no cure for Alzheimer’s disease, which affects 6.7 million Americans, and this is why early detection is particularly important, Reiss explains. By the time Alzheimer’s has advanced, a lot of damage has been done, and many nerve cells have died. This damage cannot be repaired.
Scientists are therefore focusing their efforts on developing treatments that can be used early to prevent brain destruction and preserve as much function as possible, but diagnosing early is crucial for this approach to work.
Some drugs, including one called Leqembi, have recently received FDA approvals to treat early stage Alzheimer’s disease. Studies showed that Leqembi effectively slowed the cognitive decline of patients in the early stages of Alzheimer’s.
“We want tools like the Tau 217 blood test to catch early Alzheimer’s disease or mild cognitive impairment so we can intervene right away,” Reiss says. “Although our treatments are limited now, the field is moving forward fast and there is hope for better therapies on the horizon.”