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Blood tests can help diagnose Alzheimer's, but accuracy varies : Shots - Health
News A new generation of blood tests can help doctors diagnose Alzheimer's
without a brain scan or spinal tap. But only a few perform as well as
traditional tests.


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TREATMENTS


BLOOD TESTS CAN HELP DIAGNOSE ALZHEIMER'S — IF THEY'RE ACCURATE ENOUGH. NOT ALL
ARE

January 11, 20245:00 AM ET

Jon Hamilton

BLOOD TESTS CAN HELP DIAGNOSE ALZHEIMER'S — IF THEY'RE ACCURATE ENOUGH. NOT ALL
ARE

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Newer blood tests can help doctors diagnose Alzheimer's disease without a brain
scan or spinal tap. But some tests are more accurate than others. Tek
Image/Science Photo Library/Getty Images hide caption

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Tek Image/Science Photo Library/Getty Images


Newer blood tests can help doctors diagnose Alzheimer's disease without a brain
scan or spinal tap. But some tests are more accurate than others.

Tek Image/Science Photo Library/Getty Images

A new generation of blood tests is poised to change the way doctors determine
whether patients with memory loss also have Alzheimer's disease.

The tests detect substances in the blood that indicate the presence of sticky
amyloid plaques in the brain — a hallmark of Alzheimer's. So these tests have
the potential to replace current diagnostic procedures, like costly PET scans
and uncomfortable spinal taps.

Blood tests also promise to provide doctors with a quick way to identify
patients who could benefit from new drugs that remove amyloid from the brain.

But the accuracy of the tests still varies widely.

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"Some of them are really good, and some of them are really bad," says Dr.
Suzanne Schindler, a dementia specialist at Washington University School of
Medicine in St. Louis.


THE SEARCH FOR PLAQUES AND TANGLES

Blood tests represent the latest advance in efforts to detect the buildup of
amyloid plaques and fibrous tangles in the brain.

"It used to be that the only way you could definitively diagnose someone with
Alzheimer disease is by doing an autopsy," Schindler says.

Then, starting in the early 2000s, scientists found ways to detect plaques and
tangles using PET scans and tests of spinal fluid. There are now versions of
both approaches that are approved by the Food and Drug Administration.

But the scans are costly, and spinal taps are unpopular with many doctors and
patients. Both also require expertise that is in short supply.

So Schindler and her colleagues got a lot of attention in 2019 when they
published a paper showing that amyloid plaques could be revealed by a blood
test.

"Since then, I've probably had 100 people email me wanting a test," Schindler
says. "In many cases, they are people who had family members who had Alzheimer's
disease, and this is their biggest fear."



Today, labs offer more than a dozen Alzheimer's blood tests.

"The technology has really developed very quickly," Schindler says. "People see
the dollar signs, and it's very doable to get into the market."

That market is potentially vast because more than 6 million people in the United
States have Alzheimer's and an even larger number are at risk for the disease.


FDA'S LACK OF APPROVAL

But there's not much regulation of existing blood tests for Alzheimer's. So far,
none has been approved by the FDA.

Instead they are marketed as laboratory developed tests, a special category that
usually receives minimal FDA oversight. (This past October, the FDA proposed a
rule that would increase scrutiny of these tests.)

For now, though, "you can have a test for Alzheimer disease that's not very
good," Schindler says, "but as long as you get similar results over time you can
market it."

This means that many tests, if used on the population that typically visits a
dementia specialist, would misdiagnose about one in four patients, Schindler
says.

And the accuracy would be worse if the tests were used on a population at lower
risk, speakers told a press conference on Alzheimer's blood testing at the
Society for Neuroscience meeting in November.

"When you're assessing a big group of people, a lot of whom don't have the
disease, you are going to get a lot of false positives," said Keenan Walker, an
Alzheimer's researcher at the National Institute on Aging at the National
Institutes of Health.

That's why it's so important to use the best blood tests, says Dr. Randall
Bateman, a professor of neurology at Washington University in St. Louis.

"The one we developed can be 95% accurate," he says, "so now these blood tests
are rivaling the performance of the PET scans and the spinal taps that we've
traditionally used."




TESTING FOR TREATMENT

Interest in blood tests has soared since July, when the FDA fully approved
Leqembi (lecanemab), the first drug shown to slow the progression of
Alzheimer's.

A second Alzheimer's drug, aducanumab, had received a limited FDA approval in
2021, and a third, donanemab, is likely to get full approval in the next few
months.

"For the first time ever, right, Alzheimer's doctors are now able to treat
patients with these drugs," Bateman says.

All three drugs remove amyloid from the brain. But to prescribe them, doctors
need to show that amyloid plaques are present.

That needs to happen quickly, Bateman says, while a patient is still in the
early stages of the disease.

"There's a time window where there's a benefit," Bateman says. "And if they're
going to be treated in that time window, you almost have to have blood tests."

That's because most doctors aren't equipped to immediately offer a brain scan or
a spinal tap.

The need for testing will increase if the existing Alzheimer's drugs are found
to be most effective in patients who aren't yet showing any signs of memory
impairment or thinking problems.

"The challenge then will be: How do we know who to treat if they don't even have
symptoms?" Bateman says.

The answer, he says, will be the blood tests, which can detect brain changes
long before patients develop problems with thinking and memory.

Bateman says that eventually, blood tests for Alzheimer's could even become a
part of a routine doctor visit for people older than 50.

"They go into their regular doctor's office for a checkup," he says, "[and]
blood pressure is checked, cholesterol is checked and a screening test for
amyloid plaques is checked."

Some of the scientists at the Society for Neuroscience session agreed.

"It's likely that in the future anyone over the age of 60 will get an
Alzheimer's test," said Virginia Man-Yee Lee, director of the Center for
Neurodegenerative Disease Research at the University of Pennsylvania.



When that day comes, Bateman says, it will be critical to ensure that every
blood test for Alzheimer's is as accurate as possible.

 * lecanemab
 * blood test
 * amyloid
 * Alzheimer's
 * dementia
 * Alzheimer's disease

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