New blood tests could help doctors diagnose Alzheimer’s disease more quickly and accurately, although some appear to work much better than others, researchers reported Sunday.
It’s hard to know whether memory problems are due to Alzheimer’s. That requires confirming one of the disease’s hallmarks — the buildup of a sticky protein called beta-amyloid — with a hard-to-obtain brain scan or an uncomfortable spinal tap. Many patients are diagnosed based on symptoms and cognitive tests.
Drugmakers have begun offering a range of tests that can detect certain signs of Alzheimer’s in the blood. Scientists are excited about their potential, but the tests are not yet widely used because there is little data to guide doctors on which type to order and when. None of them have been formally approved by the Food and Drug Administration, and there is little insurance coverage.
“Which tests can we trust?” asked Suzanne Schindler, a neurologist at Washington University in St. Louis who is involved in a research project on the subject. While some are highly accurate, “other tests are not much better than flipping a coin.”
Demand for early diagnosis of Alzheimer’s is increasing
More than 6 million people in the United States and millions more worldwide suffer from Alzheimer’s, the most common form of dementia. Its telltale “biomarkers” are brain-clogging amyloid plaques and the abnormal tau protein that causes brain cell death.
The new drugs Leqembi and Kisunla may slow the worsening of symptoms somewhat by clearing amyloid from the brain. But they work only in the earliest stages of Alzheimer’s, and proving that patients are eligible in time can be difficult. Measuring amyloid in spinal fluid is invasive. A special PET scanner to detect plaques is expensive, and getting an appointment can take months.
Even specialists can have a hard time determining whether a patient’s symptoms are due to Alzheimer’s or another disease.
“It is not uncommon for patients who I am convinced have Alzheimer’s, but I test them and they come back negative,” Schindler explains.
New study suggests blood tests for Alzheimer’s may be easier and faster
Until now, blood tests have been used mostly in carefully controlled research settings. But a new study in Sweden involving about 1,200 patients shows they can also work in the real-world hustle and bustle of doctors’ offices, particularly for primary care physicians, who see many more people with memory problems than specialists do but have fewer tools to assess them.
In the study, patients who saw a primary care doctor or specialist for memory problems received an initial diagnosis using traditional tests, donated blood for testing, and underwent a confirmatory spinal tap or brain scan.
Blood tests were much more accurate, Lund University researchers reported Sunday at the Alzheimer’s Association International Conference in Philadelphia. The initial diagnosis by primary care physicians was 61 percent accurate, and that by specialists 73 percent accurate, but the blood test was 91 percent accurate, according to the results, also published in the Journal of the American Medical Association.
Which blood tests work best to detect Alzheimer’s?
According to John Hsiao of the National Institute on Aging, the variety is almost like the Wild West. They measure different biomarkers in different ways.
Doctors and researchers should only use blood tests with an accuracy rate greater than 90 percent, according to Maria Carrillo, chief scientific officer of the Alzheimer’s Association.
Carrillo and Hsiao agreed that the current tests most likely to meet that requirement measure p-tau217. Schindler helped lead a rare head-to-head comparison of several types of blood tests, funded by the National Institutes of Health Foundation, that came to the same conclusion.
That type of test measures a form of tau that correlates with how much plaque buildup a person has, Schindler said. A high level indicates a high likelihood that the person has Alzheimer’s, while a low level indicates it’s probably not the cause of the memory loss.
Several companies are developing tests for p-tau217, including ALZpath Inc, Roche, Eli Lilly and C2N Diagnostics, which supplied the version used in the Swedish study.
Who should use blood tests to detect Alzheimer’s?
Only doctors can order them from drug companies. The Alzheimer’s Association is developing guidelines, and several companies are planning to apply for FDA approval, which would clarify proper use.
For now, Carrillo says doctors should use blood tests only on people with memory problems, after checking the accuracy of the type they order.
For primary care physicians in particular, “it has great potential to help them decide who to give a reassuring message to and who to send to memory specialists,” said Sebastian Palmqvist, a researcher at Lund University, who led the Swedish study with specialist Oskar Hansson.
According to Schindler, testing is not yet indicated for people who are asymptomatic but concerned about the possibility of Alzheimer’s in their family, unless it is to participate in research studies.
That’s partly because amyloid buildup can begin two decades before the first sign of memory problems, and so far there are no preventative measures beyond basic advice to eat healthy, exercise and get enough sleep. But there are studies underway testing potential therapies for people at high risk of Alzheimer’s, and some involve blood tests.
