FDA clears blood test to help rule out Alzheimer’s disease in people showing symptoms

By Jacqueline Howard, CNN

(CNN) — The US Food and Drug Administration has given clearance to another blood test to help assess Alzheimer’s disease and other causes of cognitive decline, providing a broader understanding of when the disease can be ruled out.

Roche Diagnostics said Monday that its Elecsys pTau181 test, developed in collaboration with Eli Lilly, could be used by primary care physicians to help identify patients who are unlikely to have Alzheimer’s disease, while those with a positive result would be recommended for further testing.

The test is intended for adults 55 and older in the United States who are showing signs or symptoms of cognitive decline.

“By bringing Alzheimer’s blood-based biomarker testing into primary care, we can help patients and their clinicians get answers sooner to support them earlier in their journeys,” Brad Moore, president and CEO of Roche Diagnostics North America, said in the announcement.

It’s estimated that more than 2 in 5 people over the age of 55 in the United States – about 42% – will develop dementia in their later years. And about 92% of adults with mild cognitive impairment may go undiagnosed.

“This is another important step toward expanding access to Alzheimer’s disease diagnostic tools,” Dr. Joanne Pike, Alzheimer’s Association president and chief executive officer, said in a news release Monday.

“At the same time, it is important to understand this test is designed to rule out the presence of amyloid plaques. It is not a test that will give an Alzheimer’s disease diagnosis, nor is it a standalone tool for detection,” she said. “By using a ‘rule out’ initial tool in the primary care setting, we can help people who are not living with Alzheimer’s get to the root of their cognitive symptoms faster, while ensuring those who may have the disease are referred for appropriate testing, definitive diagnosis and early treatment.”

Someone who tests negative for Alzheimer’s disease would require a different treatment approach for their cognitive decline, for instance. And “primary care clinicians can better guide appropriate referrals so neurologists can focus on the patients most likely to need advanced evaluation and treatment,” according to Roche’s announcement.

The Elecsys pTau181 test is the second blood-based biomarker test to receive FDA clearance for Alzheimer’s disease this year. The first was biotech company Fujirebio’s Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio, which got the green light in May.

Roche’s Elecsys pTau181 test works by measuring the protein pTau181 in blood plasma; higher levels of this protein are associated with Alzheimer’s disease and other neurodegenerative diseases. It’s a slightly different testing approach than Fujirebio’s Lumipulse test, which relies on a ratio of two proteins, pTau217 and beta-amyloid 1-42, to detect early signs of disease.

Having access to different blood-based tests that measure different biomarkers can help inform and provide a broader understanding of someone’s brain health when testing for early Alzheimer’s disease, said preventive neurologist Dr. Richard Isaacson, who established one of the first Alzheimer’s prevention clinics in the United States.

Therefore, Isaacson said, he would use the newly cleared Roche test alongside other assessments.

“This single Roche test is looking at pTau181 as a single protein marker. But for people who are at risk for Alzheimer’s, to truly have the best accuracy and the most granularity to understand what’s going on, we’re going to need a panel of tests. And then we’re going to need to follow these tests over time,” Isaacson said.

When someone is showing signs or symptoms of Alzheimer’s, “in theory, the amyloid protein builds up in the brain first, followed by pTau181, which comes next, and then the next one should be pTau217,” Isaacson said.

“To more accurately stage disease and track progression over time, I never order one single test. I only order a panel of tests. We’re not at the time yet where one marker is the ‘be all and end all.’ It’s more complicated than that,” he said. “While there are now resources available to learn about Alzheimer’s risk factors and what these new blood tests might mean, these are still early days.”

In a clinical study involving 312 participants, the newly cleared Elecsys pTau181 test was found to correctly identify people without Alzheimer’s pathology in 97.9% of cases, known as its negative predictive value, according to Roche.

“In other words, when the test result is negative, there’s a very high likelihood the person does not have Alzheimer’s-related pathology,” Dr. Laura Parnas, director of medical and scientific affairs at Roche Diagnostics, said in an email. “However, it’s important to note that for patients with a positive result, further clinical investigations and confirmatory testing for the amyloid pathology is needed for the final diagnosis of Alzheimer’s.”

The company said that it has about 4,500 Roche instruments installed in clinical laboratories across the United States and that it is “well positioned to rapidly integrate the Elecsys pTau181 test” into that infrastructure.

But Isaacson said he would like to see more data on the test’s sensitivity, the likelihood of getting a false positive result and how accurately it can identify disease.

“We have to be very cautious with mass adoption of these blood tests because of the potential false positives,” Isaacson said. “The medical field is still learning how to use these tests and how to apply these test results in clinical practice.”

There are a variety of laboratory-developed tests on the market that can be used to detect blood-based biomarkers associated with Alzheimer’s, as well as experimental tests – but blood testing remains an early, albeit prominent, part of dementia research.

“The ability to diagnose Alzheimer’s earlier with a simple blood test, like we do for cholesterol, is a game changer, allowing more patients to receive treatment options that have the potential to significantly slow or even prevent the disease,” Dr. Howard Fillit, co-founder and chief science officer at the Alzheimer’s Drug Discovery Foundation, said in an email in May when the Lumipulse test received FDA clearance.

“This is a clear example of the new era of Alzheimer’s research where innovation, science and technology come together to develop more accessible, affordable and scalable tools that will pave the way for additional regulatory approvals of diagnostic tools,” he wrote.

Now, with the clearance of Roche’s Elecysys test, Isaacson said he remains cautiously optimistic about the future of blood-based testing for Alzheimer’s disease.

“I feel strongly that we’re in the first inning of a nine-inning baseball game, so to speak,” he said. “Right now, we’re just seeing the initial cusp of testing availability.”

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