For decades, the only way to confirm that someone had Alzheimer’s disease was by autopsy after death, when pathologists could confirm amyloid plaques, which are hallmarks of the disease, in the brain. Doctors now use a combination of factors to diagnose Alzheimer’s, including reports from patients and their caregivers about changes in memory or other cognitive functions, performance on cognitive tests, brain imaging, and tests of spinal fluid. But some of these measures can be subjective, invasive, expensive, or hard to assess.
Enter the blood tests. There are now four blood tests cleared by the U.S. Food and Drug Administration (FDA) to detect the earliest signs of the neurodegenerative disease: an important advance in helping to diagnose Alzheimer’s in more people, as well as detecting it earlier in the disease course.
“This is a very exciting time for the field,” says Dr. Eric Reiman, CEO emeritus and lead researcher at the Banner Alzheimer’s Institute in Phoenix. “We’re going to start personalizing Alzheimer’s care similar to cancer, where we can inform diagnosis, prognosis, and staging to further inform disease severity.”
The two newest blood tests cleared by the U.S. Food and Drug Administration (FDA) in August make blood tests for Alzheimer's disease more widely available for doctors to prescribe—and in a younger population of people—for the first time. But that doesn't mean everyone should get one. Here's what to know about the available blood tests for Alzheimer's disease and when experts recommend taking them.
The first blood test for the disease, made by Fujirebio, was cleared by the FDA in May 2025. It determines the ratio of two key Alzheimer’s proteins—a form of beta amyloid and a form of tau—which reflects whether amyloid plaques are accumulating in the brain. But the test can only be run on specialized equipment and therefore isn't widely available in commercial labs.
The second test, made by Roche and FDA-cleared in October 2025, detects levels of a version of tau that correlates with the buildup of amyloid plaques. It's the first Alzheimer’s blood test that primary care physicians can prescribe to rule out the disease.
The newest Alzheimer's blood tests
The latest two tests, cleared in August, are intended to make diagnosing Alzheimer’s disease easier and more accurate.
PrecivityAD2, a new blood test from the diagnostics company C2N, is based on an earlier version of the company's test that was available only via certified labs. It uses a technology called mass spectrometry that is a more sophisticated way of picking up amyloid and tau compared to traditional assays. It provides a probability score that reflects how likely a person is to have amyloid plaques in the brain. Major laboratories as well as specific clinic and health system labs are able to perform it, so it is more widely available for doctors to prescribe.
Because PrecivityAD2 was studied in younger populations with a higher family risk of developing Alzheimer’s, it is also the first test cleared to use in people as young as 40 who show signs of cognitive problems. (The other blood tests are generally for people in their mid-50s or older.) "Because of the ability to go after individuals who represent the earliest stages of the disease process, we now have the opportunity to provide early diagnosis and then think about what should come next in managing that patient,” says Dr. Joel Braunstein, cofounder and CEO of C2N.
The other newly cleared test, from Roche, is called the Elecsys ptau217 plasma test and looks specifically for a changed version of tau—called ptau217—that appears when amyloid starts to accumulate in the brain. For people with memory issues or other cognitive complaints, the test can help them and their doctors to determine if the cause is likely due to Alzheimer’s disease or not. “It’s the most useful [test] and has the highest sensitivity and specificity,” says Dr. Thomas Wisniewski, professor of neurology, pathology and psychiatry and director of the Alzheimer’s Disease Research Center at NYU Langone Health. “We’ve been using these blood tests on the research side for a decade or so, so we have long experience knowing their utility.”
All of the tests are designed for people who are showing signs or symptoms of brain lapses or memory issues. While blood tests are relatively easy to administer and are generally used to screen for other conditions like diabetes or high cholesterol, in this case, they're not meant to be used as screening tools for otherwise healthy people with no cognitive symptoms to identify those who might be at higher risk of Alzheimer’s.
Once people or their loved ones start noticing changes in cognitive function, the blood tests can be a useful way to determine if the reason for those changes is related to Alzheimer’s or something else.
“I worry about them being used inappropriately, especially in patients without symptoms,” says Dr. Lawren VandeVrede, assistant professor of neurology at University of California San Francisco. “One of the clear bright lines we have is that these tests are intended to identify the cause of cognitive symptoms in the context of an appropriate workup in which we look at medications, mood problems, and think of potential contributors to cognitive changes.” He says that these considerations have historically contributed to a diagnostic accuracy, without using blood tests, of about 85% for Alzheimer’s disease. Adding blood tests could increase that accuracy.
“These blood tests don’t provide definitive answers; they provide information about risk,” says Wisniewski. “So they are really for evaluating people with some sort of cognitive symptoms.”
Why can’t I take a blood test to know if I’m at risk for Alzheimer’s disease?
The main reason that these blood tests aren’t being used in people without cognitive problems is that they haven’t been studied in this group. That means that the data don’t support whether the tests would have unacceptably high rates of false positive or false negatives to be useful. Already, scientists know that looking for the Alzheimer’s proteins in people at lower risk of the disease tends to lead to more false readings.
However, that could change in a year or so when two large studies conclude. Both are studying people who do not have cognitive symptoms but do have signs of abnormal brain proteins. The trials test whether using either of the currently approved Alzheimer’s drugs, lecanemab and donanemab, in people without memory problems can reduce or clear the buildup of abnormal proteins in their brains and slow the progression of the disease. If those trials show that these drugs can slow Alzheimer's, then these blood tests may become a critical part of identifying people at the earliest stages of the disease, well before they show memory or other problems.
“Published research suggests that a third of people who are cognitively intact above a certain age will show positive biomarkers for Alzheimer’s disease, including on blood tests,” says Dr. Jason Hinman, professor of neurology and director of the Mary S. Easton Center for Alzheimer’s Research and Care at the University of California Los Angeles. That means that the blood tests could become an important part of evaluating brain health and Alzheimer's risk well before symptoms start. They could also open the door for treating people at earlier stages of the disease—if the studies support it—to protect them from advancing more quickly.
For people who start the Alzheimer’s medications, the blood tests could also play an important role in tracking how well the drugs work in reducing or clearing the plaques from the brain. In a recent study published in Alzheimer’s & Dementia, scientists in Korea reported that patients taking lecanemab showed a drop in levels of ptau217 three to six months after beginning the drug, and that drop was linked to slower cognitive decline as measured in cognitive tests.
What are the differences between the tests?
All of the blood tests look for one or both of the hallmark proteins associated with Alzheimer’s, but with different levels of sensitivity and specificity. Most experts agree that levels of ptau217 provide the most reliable sign of Alzheimer’s disease so far. “The ptau217 test was a real surprise,” says VandeVrede. “We didn’t know how good it would be, how accurate it was.”
PrecivityAD2, because it was studied in younger people, might be useful for people who have a family history of the disease and are starting to show signs of cognitive problems or memory loss.
The blood tests also put more information in the hands of primary care doctors, who are often the first to confront cognitive changes in patients. Recent studies showed that primary care physicians—not just specialists—are able to interpret and manage Alzheimer’s diagnoses using blood tests. Having blood tests to confirm a potential Alzheimer’s diagnosis also helps primary care physicians triage which patients might need to be referred to specialists for further confirmatory testing, such as an amyloid PET scan or a spinal fluid test. “Blood biomarker [tests] are democratizing the diagnosis of Alzheimer’s disease," says VandeVrede. "I am seeing patients show up much earlier than they used to, because I think these tests are helping more people to take the symptoms seriously.”
To help primary care doctors interpret the blood tests, the Alzheimer’s Association created guidelines by which doctors should first establish that the patient shows signs or symptoms of cognitive issues, and secondly rule out other potential causes of those problems, including depression, medications, vitamin deficiencies, and even sleep disorders. “We know that a lot more people will be asking for these blood tests,” says Maria Carrillo, chief science officer at the Alzheimer’s Association. “So the upshot of our guidance is triaging patients. A lot has to be done before patients should be getting a blood test for Alzheimer’s.”
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