WASHINGTON — New blood tests could help doctors diagnose Alzheimer’s disease faster and more accurately, researchers reported Sunday. But some appear to work much better than others.
It’s tricky to tell whether memory problems are caused by Alzheimer’s. That requires confirming one of the disease’s hallmark signs — a buildup of a sticky protein called beta-amyloid — with a hard-to-obtain brain scan or an uncomfortable spinal tap. Many patients are instead diagnosed based on symptoms and cognitive tests.
Labs have begun offering several tests that can detect certain signs of Alzheimer’s in the blood. Scientists are excited about their potential, but the tests aren’t widely used because there’s little data to help doctors decide what kind to order and when. The U.S. Food and Drug Administration hasn’t formally approved any of them, and insurance coverage is limited.
“Which tests can we trust?” asked Dr. Suzanne Schindler, a neurologist at Washington University in St. Louis who is part of a research project investigating this. While some are very accurate, “other tests are no better than flipping a coin.”
The demand for earlier diagnosis of Alzheimer’s is increasing
More than 6 million people in the United States and millions more worldwide have Alzheimer’s, the most common form of dementia. Its telltale “biomarkers” are brain-clogging amyloid plaques and abnormal tau protein that leads to neuron-killing tangles.
New drugs, Leqembi and Kisunla, can slow the worsening of symptoms somewhat by clearing the brain of the nasty amyloid. But they work only in the earliest stages of Alzheimer’s, and it can be tricky to prove eligibility in time. Measuring amyloid in spinal fluid is invasive. A special PET scan to detect plaques is expensive, and it can take months to get an appointment.
Even specialists may have difficulty determining whether a patient’s symptoms are caused by Alzheimer’s disease or something else.
“I often have patients who I am convinced have Alzheimer’s disease. I do tests and they are negative,” Schindler said.
New research suggests blood tests for Alzheimer’s could be simpler and faster
Blood tests have so far been used mainly in carefully controlled research settings. But a new study of about 1,200 patients in Sweden shows that they can work in the real hustle and bustle of doctor’s offices — particularly general practitioners, who see far more people with memory problems than specialists do, but have fewer tools to evaluate them.
In the study, patients who went to a general practitioner or specialist for memory complaints were initially diagnosed through traditional tests. They were then given blood for testing and referred for a confirmatory lumbar puncture or brain scan.
Blood tests were much more accurate, Lund University researchers reported Sunday at the Alzheimer’s Association International Conference in Philadelphia. The primary care physicians’ initial diagnosis was 61 percent accurate, and the specialists’ was 73 percent — but the blood test was 91 percent accurate, according to the findings, also published in the Journal of the American Medical Association.
Which blood tests for Alzheimer’s work best?
There’s almost a “Wild West” in the variety that’s offered, said Dr. John Hsiao of the National Institute on Aging. They measure different biomarkers, in different ways.
Doctors and researchers should only use blood tests that have been proven to be more than 90 percent accurate, said Maria Carrillo, chief scientific officer of the Alzheimer’s Association.
Today’s tests are most likely to meet that benchmark, what’s called p-tau217, Carrillo and Hsiao agreed. Schindler helped lead an unusual head-to-head comparison of different types of blood tests, funded by the Foundation for the National Institutes of Health, that reached the same conclusion.
That type of test measures a form of tau that correlates with how much plaque someone has, Schindler explained. A high level indicates a high likelihood that the person has Alzheimer’s, while a low level indicates that it is unlikely to be the cause of memory loss.
Several companies are developing p-tau217 tests, including ALZpath Inc., Roche, Eli Lilly and C2N Diagnostics, which supplied the version used in the Swedish study.
Who are Alzheimer’s blood tests suitable for?
Only doctors can order them from labs. The Alzheimer’s Association is working on guidelines, and several companies plan to seek FDA approval, which would clarify proper use.
Carrillo said that for now, doctors should only perform blood tests on people with memory problems after checking the accuracy of the blood type they prescribe.
For GPs in particular, “it really has enormous potential to help them determine who to give a reassuring message to and who to refer to memory specialists,” said Dr Sebastian Palmqvist of Lund University, who led the Swedish study with Dr Oskar Hansson of Lund.
The tests are not yet intended for people who have no symptoms but are concerned about Alzheimer’s in their family, unless it is part of participation in research studies, Schindler stressed.
That’s partly because amyloid buildup can begin two decades before the first signs of memory problems, and so far there are no preventative measures beyond the basic advice of eating healthy, exercising and getting enough sleep. But there are ongoing studies testing possible therapies for people at high risk for Alzheimer’s, and some involve blood tests.
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.
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