Blood tests for Alzheimer’s disease could soon be done at your doctor’s office: What you need to know

• New blood tests show promise for faster, more accurate diagnosis of Alzheimer’s disease, medical researchers say.
• Many current diagnoses of Alzheimer’s disease are based on symptoms and cognitive tests, but blood tests may offer a simpler alternative.
• Blood tests measuring p-tau217, a biomarker associated with Alzheimer’s disease, are expected to become more important as FDA guidelines are established.

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 difficult to determine whether memory problems are caused by Alzheimer’s disease. That requires confirming one of the disease’s hallmarks, the buildup of a sticky protein called beta-amyloid, with a difficult brain scan or an uncomfortable spinal tap. Many patients are instead diagnosed based on symptoms and cognitive tests.

Labs have begun offering a variety of tests to detect some signs of Alzheimer’s disease in the blood. Scientists are excited about their potential, but the tests aren’t widely used yet because there’s little data to help doctors decide which tests to order and when. The U.S. Food and Drug Administration hasn’t officially approved any of them, and insurance coverage is limited.

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“What tests can we trust?” asks Dr. Suzanne Schindler, a neurologist at Washington University in St. Louis who is involved in a research project on the subject. While some are very accurate, “other tests are little better than a coin flip.”

A doctor shows the results of a PET scan that was part of a study of Alzheimer’s disease at Georgetown University Hospital on May 19, 2015, in Washington. New blood tests could help doctors diagnose Alzheimer’s disease more quickly and accurately, researchers reported Sunday. (AP Photo/Evan Vucci, file)

Demand for early diagnosis of Alzheimer’s disease increases

More than 6 million people in the United States and millions more worldwide suffer from Alzheimer’s disease, the most common form of dementia. Its telltale “biomarkers” are amyloid plaques that clog the brain and an abnormal tau protein that leads to destructive tangles of neurons.

New drugs, Leqembi and Kisunla, may slightly slow the worsening of symptoms by clearing the sticky amyloid from the brain. But they are effective only in the early stages of Alzheimer’s, and it can be difficult to prove in time that patients are eligible. Measuring amyloid in spinal fluid is invasive. A special positron emission tomography (PET) scan to spot plaques is expensive, and getting an appointment can take months.

Even specialists can have difficulty determining whether Alzheimer’s or another disease is causing a patient’s symptoms.

“It’s not uncommon for me to have patients who I’m convinced have Alzheimer’s disease. I run tests and they come back negative,” Schindler said.

New study suggests blood tests for Alzheimer’s disease may be simpler and faster

Until now, blood tests have been performed mainly in carefully controlled research settings. But a new study of 1,200 Swedish patients shows that they can also be used in the practice setting, particularly by general practitioners who see many more people with memory problems than specialists, but have fewer tools to assess them.

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

Blood tests were much more accurate, researchers from Lund University reported Sunday at the Alzheimer’s Association International Conference in Philadelphia. The initial diagnosis by general practitioners was 61 percent accurate, and by specialists, 73 percent. But the blood test was 91 percent accurate, according to the results, which were also published in the Journal of the American Medical Association.

Which blood tests are most effective for Alzheimer’s disease?

There’s almost a “Wild West” in the diversity of treatments being 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 an accuracy rate of more than 90 percent, said Maria Carrillo, chief scientific officer of the Alzheimer’s Association.

Carrillo and Hsiao agreed that the current tests most likely to meet that standard measure something called the protein p-tau217. Schindler helped lead an unusual head-to-head 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 protein that correlates with the amount of plaque a person has built up, Schindler explained. A high level indicates a high likelihood that the person has Alzheimer’s disease, while a low level indicates it’s 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 provided the version used in the Swedish study.

Who Should Have Blood Tests for Alzheimer’s Disease?

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 their appropriate use.

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

“This really has great potential to help primary care physicians determine who to send a reassuring message to and who to refer memory specialists to,” said Dr. Sebastian Palmqvist of Lund University, who led the Swedish study with Dr. Oskar Hansson of Lund.

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The tests are not yet intended for people who don’t have symptoms but are concerned about Alzheimer’s running in the family — unless that’s part of enrolling in research studies, Schindler said.

This is partly because amyloid buildup can begin 20 years before the first signs of memory problems appear, and there are no preventative measures yet beyond basic advice like eating healthy, exercising, and getting enough sleep. But studies are underway to test possible therapies for people at high risk of Alzheimer’s disease, and some include blood tests.