New blood test helps diagnose Alzheimer's. Doctors still haven't caught up: Shots

A new blood test to help detect Alzheimer's disease is ushering in a new era of diagnosis and treatment, doctors say.

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Marcus Brandt/Picture Alliance/Getty Images

A new generation of blood test promises to change the way doctors diagnose and treat Alzheimer's disease.

The test offers doctors a quick and easy way to find out whether patients with symptoms of cognitive decline also have brain changes associated with Alzheimer's disease, which requires evidence of changes before doctors can prescribe one of two recently approved drugs that can slow the progression of Alzheimer's.

As demand for these drugs increases, blood tests could play a key role in identifying patients in the early stages of Alzheimer's disease who would benefit from treatment.

But the blood tests arrived so quickly that most doctors had little direction on which patients to test or how to interpret the results, many experts said. Alzheimer's Association International Conference In Philadelphia.

“Currently, there are no guidelines regarding the use of these tests.” Dr. Eliezer MasuriahHe is director of the Neuroscience Division at the National Institute on Aging, part of the National Institutes of Health.

“This field is moving at a speed that would have been unimaginable 10 years ago,” he said. Dr. Heather WhitsonHe is a professor of medicine at Duke University and co-chaired a session on developing clinical practice guidelines for testing at the Alzheimer's disease conference.

“Blood tests for Alzheimer's are advancing incredibly quickly. [doctors] “I'm not used to the speed of change.” Dr. Suzanne SchindlerAssociate Professor of Neurology at Washington University School of Medicine in St. Louis.

Tests showed the presence of sticky amyloid plaques and tangled strands of fiber called tau in his brain. Characteristics of Alzheimer's DiseaseUntil recently, finding signs of the disease required an uncomfortable spinal tap or an expensive PET scan.

Commercial labs have offered a variety of blood tests for detecting plaques and neurofibrillary tangles in the brain for several years, but until just a few months ago, the accuracy of these tests varied widely, Schindler says, mostly because the tests measured different proteins.

That's changing, as more and more labs now offer blood tests that focus on abnormal proteins. Putau 217.

“When you look at just a population of people with cognitive impairment, these ptau217 tests perform extremely well,” Schindler said, with accuracy rates of about 90 percent.

There are currently a number of ptau217 tests available on the market, but none have been approved by the Food and Drug Administration, which means insurance companies often won't cover the cost, which typically costs hundreds of dollars.

Still, the new tests are being ordered by a growing number of physicians, not just specialists, and the general public is beginning to learn about and demand them.

Schindler says these changes signal the beginning of a new era in diagnosing and treating Alzheimer's, in which primary care physicians will play a key role.

“Doctors need to learn about these tests, because this is really coming soon,” she says.

Moving from symptoms to biology

The rise in blood tests reflects a larger change in the Alzheimer's field, experts say.

“Biological diagnosis of Alzheimer's disease is now mainstream,” Masria says. Biomarkers Instead of just focusing on clinical symptoms.”

These markers, which can be found in PET scans and cerebrospinal fluid, are far more accurate than cognitive or clinical tests in determining which patients have amyloid plaques or tau tangles in their brains.

Big study They found that even dementia specialists misdiagnose about one in four patients who underwent cognitive evaluations, whereas blood tests only misdiagnose about one in 10.

For example, Ptau217 is a biomarker that detects an abnormal version of the tau protein found in neurons affected by Alzheimer's disease, where tiny amounts of this protein leak from brain cells into the bloodstream.

And remarkably, levels of this abnormal tau protein are a highly accurate predictor of the buildup of amyloid plaques that contain another abnormal protein.

Scientists are constantly discovering new blood biomarkers for Alzheimer's disease, Masria says, so it's likely that ptau217 will be combined or replaced with markers that are even more effective, or that provide different information about what's going on in the brain.

“All of this really suggests the idea of ​​using a blood test to diagnose Alzheimer's disease,” Masria says, “and I think we're very close to that.”

But many primary care physicians still don't know how to use this new diagnostic tool, Whitson said.

So she and other experts have compiled examples of patients who should and shouldn't get tested.

The “should” category includes patients who show obvious signs of cognitive impairment, she said, such as those who repeatedly ask the same questions during appointments, those who frequently forget to take their medication at home or those who can no longer manage their own finances.

In the “shouldn't” category are people who don't have symptoms of cognitive decline but are concerned about their brain health.

“Maybe there's a history of Alzheimer's in your family,” she says, “so every time you forget a name you worry that this is Alzheimer's.”

Patients without cognitive symptoms are not candidates for drug treatment and may feel unnecessarily anxious if they test positive, Whitson said.

“A certain percentage of the population has amyloid in their brain, but they go through a normal lifespan and don't have any symptoms,” she said. “We know about it.”

Diagnosis is just the first step

Despite the current confusion, experts at the Alzheimer's Conference believe that within a few years, primary care doctors will be offering blood tests to many of their older patients with memory loss, and they will know what to do if the result is, say, borderline, rather than clearly positive or negative.

But getting a diagnosis is just the first step in a long journey. Dr. Howard FillittChief Scientific Officer at the Alzheimer's Drug Discovery Foundation.

A positive test result “has big implications,” Fillitt said, and not just for the individual patient: “What does it mean for your family? What does it mean for your spouse?”

Philif says primary care physicians will soon learn to diagnose patients with the help of blood tests. “The question is whether they will spend the time needed to educate and counsel them.”

Even if that were to happen, it's not yet clear whether Medicare or other payers would cover those services.