Innovative blood test could be key to diagnosing Alzheimer's

WASHINGTON — New blood tests may help doctors diagnose Alzheimer's disease faster and more accurately, researchers reported Sunday — but some seem to work much better than others.

It's tricky to tell if memory problems are caused by Alzheimer's. That requires confirming one of the disease's hallmarks — the buildup of a sticky protein called beta-amyloid — with a hard-to-get brain scan or a nasty spinal tap. Many patients are instead diagnosed based on symptoms and cognitive testing.

Laboratories are beginning to offer a variety of tests that can detect certain signs of Alzheimer's in the blood. Scientists are excited by their potential, but the tests are not yet widely used because there is little data to guide doctors about what type to order and when. The US Food and Drug Administration has not officially approved any of them, and there is little insurance coverage.

"What tests can we trust?" asked Dr. Suzanne Schindler, a neurologist at Washington University in St. Louis. Louis who is part of a research project looking into it. While some are highly accurate, "other tests are not much better than a coin flip."

The demand for early 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 amyloid plaques that clog the brain and abnormal tau protein that leads to tangles that kill neurons.

The new drugs, Leqembi and Kisunla, can modestly slow the worsening of symptoms by removing heavy amyloid from the brain. But they only work in the earliest stages of Alzheimer's, and proving patients' eligibility in time can be difficult. Measuring amyloid in spinal fluid is invasive. A special PET scan to detect plaques is expensive and getting an appointment can take months.

Even specialists can struggle to tell whether Alzheimer's or something else is to blame for a patient's symptoms.

"I have patients not infrequently who I'm convinced have Alzheimer's disease and I test them and they're 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 they can also work in the real-world chaos of doctors' offices — especially primary care doctors who see far more people with memory problems than specialists but have fewer tools to evaluate them.

In the study, patients who saw either a primary care physician or a memory specialist received an initial diagnosis using traditional screenings, gave blood for testing, and were sent for a spinal tap or brain scan.

The blood test was much more accurate, Lund University researchers reported Sunday at the Alzheimer's Association International Conference in Philadelphia. Primary care doctors' initial diagnosis was 61% accurate and specialists' 73% - but the blood test was 91% accurate, according to the findings, which were also published in the Journal of the American Medical Association.

Which blood tests for Alzheimer's function are best?

There is almost "a Wild West" in the variety on offer, 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 proven to have an accuracy rate greater than 90%, said Alzheimer's Association chief scientific officer Maria Carrillo.

Today's tests most likely to meet that benchmark measure what's called p-tau217, Carrillo and Hsiao agreed. Schindler helped lead an unusual direct comparison of several types of blood tests, funded by the Foundation for the National Institutes of Health, that came to the same conclusion.

This type of test measures a form of tau that correlates with how much plaque someone accumulates, Schindler explained. A high level signals a strong likelihood that the person has Alzheimer's while a low level indicates that it is probably not the cause of the 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 should use blood tests for Alzheimer's?

Only doctors can order them from laboratories. The Alzheimer's Association is working on guidelines, and some companies plan to seek FDA approval, which would clarify appropriate use.

For now, Carrillo said doctors should only use the blood test on people with memory problems after checking the accuracy of the type they order.

Especially for primary care physicians, "there's really a lot of potential in helping them sort out who to give a reassuring message to and who to send to memory specialists," said Dr. Sebastian Palmqvist of Lund University, who led the Swedish study with Dr. Oscar Hanson.

The tests aren't yet for people who don't have symptoms but worry about Alzheimer's running in the family — unless it's part of research study enrollment, Schindler pointed out.

That's partly because amyloid buildup can begin two decades before the first sign of memory problems, and until now there are no preventative steps beyond basic advice to eat healthy, exercise and get enough sleep. But there are studies testing potential therapies for people at high risk of Alzheimer's, and some involve blood testing.