Alzheimer’s disease blood test may be coming, study at Alzheimer's Association International Conference says

New blood tests could help doctors diagnose Alzheimer’s disease faster and more accurately, researchers reported Sunday — but none has been approved by the federal Food and Drug Administration, and some appear to work far better than others.

Blood tests so far have been used mostly in carefully controlled research settings. But a new study, reported Sunday at the Alzheimer's Association International Conference in Philadelphia, of about 1,200 patients in Sweden found that they also can work in the real-world bustle 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, whose findings also were published in the Journal of the American Medical Association, people who saw either a primary-care doctor or a specialist for memory complaints got an initial diagnosis using traditional exams, gave blood for testing and were sent for a confirmatory spinal tap or brain scan.

It turned out that blood testing was far more accurate, the researchers from Sweden's Lund University told the Philadelphia conference held by the Chicago-based Alzheimer's Association.

The primary-care doctors’ initial diagnosis was 61% accurate and the specialists’ 73% — but the blood test was 91% accurate, according to the new findings.

But a big question remains over which tests to use, experts say.

There’s almost “a wild West” in the variety being offered, according to Dr. John Hsiao of the National Institute on Aging. They measure different biomarkers in different ways.

Doctors and researchers should use only those blood tests proven to have a greater than 90% accuracy rate, according to Maria Carrillo, the Alzheimer’s Association's chief science officer.

The tests that are available today that are most likely to meet that standard measure what’s called p-tau217, according to Carrillo and Hsiao

Dr. Suzanne Schindler, a neurologist at Washington University in St. Louis, helped lead an unusual direct comparison of several kinds of blood tests funded by the Foundation for the National Institutes of Health, that came to the same conclusion.

This particular type of test measures a form of tau protein that correlates with how much plaque buildup a person's brain has, Schindler said. A high level signals a strong likelihood the person has Alzheimer’s, and a low level indicates that’s probably not the cause of memory loss, she said.

Several companies — including ALZpath Inc., Roche, Eli Lilly and C2N Diagnostics, which supplied the version used in the Swedish study — are developing p-tau217 tests.

Labs have begun offering a variety of tests that can detect certain signs of Alzheimer’s in blood. That has scientists excited about their potential. But the tests aren’t widely used yet because there’s little data to guide doctors about which kind to order and when. The FDA hasn't approved any of them. And there’s little insurance coverage.

Schindler said some of the other tests now available for Alzheimer's "are not much better than a flip of a coin.”

So the key question, she said, is: "What tests can we trust?"

It’s tricky to tell whether memory problems are caused by Alzheimer’s. That requires confirming one of the disease’s hallmark signs — buildup of a sticky protein called beta-amyloid — with a hard-to-get brain scan or uncomfortable spinal tap. Instead, many people end up being diagnosed based on symptoms and cognitive exams.

Who should use blood tests for Alzheimer’s?

Only doctors can order the blood tests from labs. The Alzheimer’s Association is working on guidelines, and several companies plan to seek FDA approval, which would clarify proper use.

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

Especially for primary-care physicians, “It really has great potential to help them in sorting out who to give a reassuring message and who to send on to memory specialists,” said Dr. Sebastian Palmqvist of Lund University, who led the Swedish study with Lund’s Dr. Oskar Hansson.

The tests aren’t yet for people who don’t have symptoms but worry because family members have had Alzheimer’s — unless it’s part of enrollment in research studies, Schindler said.

That’s partly because amyloid buildup can begin two decades before the first sign of memory problems, and so far there are no preventive steps other than basic advice to eat healthy, exercise and get enough sleep. But there are studies underway testing possible therapies for people at high risk of Alzheimer’s, and some include blood testing.

It's estimated that more than six million people in the United States and millions more around the world have Alzheimer’s, which is the most common form of dementia. Its telltale biomarkers are brain-clogging amyloid plaques and abnormal tau protein that leads to neuron-killing tangles.

The new drugs Leqembi and Kisunla can modestly slow worsening symptoms by removing gunky amyloid from the brain. But they work only in the earliest stages of Alzheimer’s — and proving patients qualify in time can be difficult. Measuring amyloid in spinal fluid is, of course, invasive. Imaging done with special PET scan to spot plaques is costly, and just getting an appointment for one of these can take months.

Even specialists can struggle to tell whether it's Alzheimer’s or something else that's to blame for a person’s symptoms.

“I have patients not infrequently who I am convinced have Alzheimer’s disease," Schindler said. "And I do testing, and it’s negative."