By Robin Foster
TUESDAY, July 28, 2020 (HealthDay News) -- A new blood test offers hope that doctors may soon be able to diagnose Alzheimer's disease with astonishing accuracy.
A study led by Swedish researchers found the test did more than differentiate between Alzheimer's and other types of dementia. It also spotted signs of Alzheimer's two decades before symptoms appeared in people who were genetically predisposed to develop the degenerative disease.
How? It measures levels of a specific tau protein, called p-tau217, that has long been linked to Alzheimer's.
"This blood test very, very accurately predicts who's got Alzheimer's disease in their brain, including people who seem to be normal," Dr. Michael Weiner, an Alzheimer's disease researcher at the University of California, San Francisco, told the New York Times. "It's not a cure, it's not a treatment, but you can't treat the disease without being able to diagnose it. And accurate, low-cost diagnosis is really exciting, so it's a breakthrough."
The Swedish test, and two other studies looking at tau tests, were presented Tuesday during the Alzheimer's Association virtual annual meeting. The Swedish study was also published July 28 in the Journal of the American Medical Association.
The Swedish test was able to differentiate whether people with dementia had Alzheimer's rather than other neurodegenerative disorders 96% of the time, said study senior author Dr. Oskar Hansson, a professor of clinical memory research at Lund University in Sweden.
"The p-tau217 blood test has great promise in the diagnosis, early detection and study of Alzheimer's," Hansson said in a university news release. Though more work is needed to refine the test and try it in more people, it "might become especially useful to improve the recognition, diagnosis and care of people in the primary care setting," he added.
In a group of nearly 700 people from Sweden, the test was similar in accuracy to PET scans and spinal taps, and it was better than MRI scans and blood tests for amyloid, another protein linked to Alzheimer's. The test was also nearly as accurate as autopsies performed on deceased people's brains in a separate arm of the study, the researchers added.
PET scans and spinal taps, which are far more costly than blood tests, can detect elevated levels of amyloid protein. But amyloid levels alone aren't enough to diagnose Alzheimer's because some people with high levels of it don't develop the disease, experts explained.
"Just saying you have amyloid in the brain through a PET scan today does not tell you they have tau, and that's why it is not a diagnostic for Alzheimer's," Maria Carrillo, chief science officer at the Alzheimer's Association, told the Times. But the tau blood test appears to detect the presence of both amyloid plaques and tau tangles, she said.
"This test really opens up the possibility of being able to use a blood test in the clinic to diagnose someone more definitely with Alzheimer's," Carrillo told the newspaper. "Amazing, isn't it? I mean, really, five years ago, I would have told you it was science fiction."
In the Swedish study, people with Alzheimer's had seven times more of p-tau217 than people without any dementia or those with other neurological disorders, like frontotemporal dementia, vascular dementia or Parkinson's disease, Hansson noted. "This is so specific for Alzheimer's disease," he told the Times.
Such a blood test would speed up and lower the cost of clinical trials and allow doctors to diagnose or rule out Alzheimer's in patients with dementia.
Two other teams presented research on tau tests at the Alzheimer's Association meeting. One test, conducted by researchers at Washington University in St. Louis, used a testing method that detects molecules of tau or amyloid. That research, published July 28 in the Journal of Experimental Medicine, found that the same form of tau tracked in the Swedish study correlated more closely to amyloid buildup in the brain than another form of tau, the Times reported.
"The finding of a unique tau species that is closely linked to changes caused by amyloid plaques will help to identify and predict people who have or will likely develop Alzheimer's disease," said senior study author Dr. Randall Bateman, the Charles F. and Joanne Knight Distinguished Professor of Neurology at Washington University. "This will greatly accelerate research studies, including finding new treatments, as well as improving diagnosis in the clinic with a simple blood test."
In a third study presented at the same meeting, Dr. Adam Boxer, a neurologist at the University of California, San Francisco, and Elisabeth Thijssen, a visiting graduate student, found both forms of tau could distinguish Alzheimer's from frontotemporal dementia. Research presented at meetings is considered preliminary until published in a peer-reviewed journal.
Alzheimer's is an incurable disease that affects an estimated 5.8 million Americans aged 65 and older. Without the discovery of successful prevention therapies, the number of U.S. cases is projected to reach nearly 14 million by 2050, the Swedish researchers said.