Though some blood tests are already on the market, some experts are skeptical about their role in clinical practice.
Getting an accurate Alzheimer’s diagnosis can take years — and several visits to the doctor. After taking a medical history, neurological exam, and blood tests to rule out other conditions, typically, doctors will order an amyloid PET scan or lumbar puncture to confirm the presence of amyloid plaques in the brain. These procedures often come with a waitlist, and they might require people to travel a significant distance to a specialized center or clinic.
But every year lost to this process is a year Alzheimer’s progresses further. Soon, patients are no no longer candidates for the disease-modifying therapies — like Leqembi and Kisunla — designed for the earliest stages of the disease, nor can they qualify for the clinical trials testing more drugs like these.
Blood tests measure fragments of various Alzheimer’s proteins that make their way from the brain and into the bloodstream. The best biomarkers provide a proxy measurement of whether you have Alzheimer’s pathology — beta-amyloid plaques and tau tangles — in the brain.
Your Guide to Alzheimer’s Blood Tests: Pricing, Accuracy, and Where to Get One
And they hold great promise when it comes to diagnosis: Measuring Alzheimer’s biomarkers in the blood is considerably cheaper, easier to do, and less invasive than a lumbar puncture or an amyloid PET scan. They could speed up this process and make Alzheimer’s diagnosis a more accessible — and faster — process.
“We’ve had tremendous advances in blood tests for Alzheimer’s disease over the past few years, and to me it’s revolutionary,” Dr. Howard Fillit at the Alzheimer’s Drug Discovery Foundation told Being Patient.
Some blood tests are already on the market for doctors to order, and many news sites have touted them as a game changer.
“None of these tests have been FDA approved,” Dr. Nicholas Ashton, neurologist and senior director of Banner Health’s Research Blood-Based Biomarker Program told Being Patient. “None of them have really been given that stamp of approval yet that these should be used clinically.”
As a result, there are many blood tests on the market available to doctors but they aren’t standardized — some tests are much better than others and it can be hard for doctors to pick the best one. Experts are also split on whether blood tests, even after FDA approval, can replace PET scans and lumbar punctures altogether.
Can blood tests diagnose Alzheimer’s disease on their own?
There’s plenty of discussion about these “Alzheimer’s blood tests,” but in fact, they’re not designed to actually diagnose the disease:
“You don’t diagnose someone in a clinic based on a blood test or a cerebrospinal fluid test alone,” Ashton said. “A blood test is a supportive feature to the diagnosis, it’s not the sole diagnosis.”
Indeed, researchers and diagnostic companies agree that the blood test alone can’t diagnose the disease, and doctors need to interpret the results in the context of a medical workup and cognitive testing.
In contrast, the newest diagnostic criteria for the disease suggest a blood test alone can be enough to diagnose the disease. The working group of scientists that developed the criteria included scientists employed by companies manufacturing blood tests.
“A blood test that is 90 percent or more accurate in the intended use population is sufficient to make a diagnosis of Alzheimer’s,” Dr. Clifford Jack, head of the working group behind the updated Alzheimer’s criteria and neurologist at the Mayo Clinic told Being Patient. He emphasized that the intended use population, in this case, is people experiencing cognitive decline symptoms.
The other problem Ashton pointed to was a lack of diverse participants involved in the studies used to develop and measure the effectiveness of blood tests. Most of the studies were conducted on white participants, so it isn’t clear whether these tests work as well in Black and Hispanic Americans. Indeed, a previous study found that three of four blood tests don’t. Precivity’s test was the only blood test that was as accurate in white participants as in Black participants in the study.
“None of these tests have been FDA approved.
None of them have really been given that stamp of
approval yet that these should be used clinically.”
Until recently, blood tests didn’t even need to prove to the FDA that they work. But moving forward, new blood tests need to apply for approval from the FDA.
“I think it ultimately will be a good thing,” Fillit said of the new regulations. “But I think to transition to these new FDA regulations will require a lot of standardization, validation, and rigor that hasn’t been done for every test before.”
What blood tests should doctors use?
Blood tests measure all different types of beta-amyloid and tau — and according to Fillit, there is some consensus on which biomarker is superior.
“pTau-217 seems to be emerging as the best blood test,” he said. Fillit and Ashton agreed that Precivity’s C2N blood test, which measures these protein fragments, is one of the best available to doctors.
Precivity’s blood test is a little more expensive than other tests on the market because of the method it uses to measure proteins in the blood. Fillit added that Roche and FujiBio are also developing promising tests, though these tests are not currently available to doctors.
Will blood tests replace lumbar punctures and amyloid PET scans?
Despite their affordability and accessibility advantages, Ashton doesn’t think they’re ready to replace these other tests, which provide more information for a neurologist looking to make a diagnosis. Instead, he thinks blood tests fill the void for people who wouldn’t otherwise receive any testing.
“You have to remember that the blood test is only telling you about Alzheimer’s disease pathology,” he said. “If you can collect the cerebrospinal fluid [via lumbar puncture] and it’s accepted by the patient and it’s accepted by the clinician you get much more information.”
While blood tests are a promising innovation for helping diagnose Alzheimer’s disease, there are still many questions about how to use them in the clinic and whether they should replace other types of tests. Doctors and patients need more guidance to help them choose the right test for their patients.
