For decades, there wasn’t much good news to report about efforts to battle Alzheimer’s disease, the neurodegenerative scourge that affects nearly 7 million people in the United States. But that changed rapidly in the past year with progress on three fronts: the U.S. Food and Drug Administration’s approval of two new drugs to slow progression of the disease; new information about the genetic roots of Alzheimer’s; and encouraging recent results of a blood test that could improve early detection of Alzheimer’s.

Alzheimer’s Association researchers strongly touted the promise of the new blood test, which measures levels of two key biomarkers tied to Alzheimer’s disease. The organization’s leaders noted that blood tests generally could make Alzheimer’s disease screening and diagnosis much more widely available and less expensive for patients. In turn, patients could begin treatment when the disease is still in its early stages. Blood tests could also help to boost the number of candidates who qualify for clinical trials of new treatments.

To provide answers to your top questions about this encouraging news, we spoke with Dr. Tara Carlisle, a behavioral neurologist and assistant professor of Neurology with the University of Colorado School of Medicine, who practices at the Advanced Therapy for Neurodegenerative Disorders Clinic, a space within the University of Colorado Neurobehavior and Memory Disorders Clinic at the UCHealth Neurology Clinic – Central Park.

Carlisle explained that while the new developments related to blood tests for Alzheimer’s disease are encouraging, they also raise important questions for both patients and providers.

Is there a blood test available for Alzheimer’s disease?

Yes. In fact, several companies offer tests. They include Quest Diagnostics, ALZPath, Inc., Roche Diagnostics (developed with Eli Lilly Company), LabCorp, and C2N Diagnostics.

What do the blood tests measure?

That depends on the test. In general, the new blood tests detect levels of proteins that indicate risk for Alzheimer’s disease, Carlisle said. For example, the AD-Detect test introduced by Quest Diagnostics in 2023 measures the ratio of beta-amyloid 42 and 40. In Alzheimer’s disease, amyloid inappropriately clumps together to create sticky plaques that affect the way brain cells function and degrade cognition.

In April 2024, Quest announced a new blood test that measures levels of p-tau217, another protein associated with Alzheimer’s disease that forms tangles in the brain. The blood tests for p-tau217 can also predict whether amyloid plaques may be present, Carlisle said.

The PrecivityAD2 test from C2N Diagnostics measures both the beta-amyloid 42/40 ratio and p-tau217 levels, Carlisle said.

How accurate are the new blood tests for Alzehimer’s?

The Precivity AD2 test is “pretty accurate and specific,” Carlisle said. In a study partially funded by the National Institutes of Health that generated much attention, that blood test accurately predicted Alzheimer’s disease in 88% to 92% of participants. The result compared favorably with the current “gold standards” for diagnosing Alzheimer’s disease: lumbar punctures, which are used to draw cerebrospinal fluid and analyze it for the presence of beta-amyloid and tau; and positron emission tomography (PET) scans, which measure beta-amyloid in the brain but do not provide information about tau. The Precivity test was also significantly more accurate than clinical evaluations by providers in memory centers (73%) or primary care facilities (61%).

The numbers should be viewed from a broad perspective, Carlisle cautioned. For example, the PrecivityAD2 study was conducted with Swedish patients. The National Institute on Aging called for additional studies of more diverse populations. Many other factors can affect the accuracy of the tests, Carlisle added.

“There are different groups that are developing different tests in different locations, but it is important to understand that some of the blood-based biomarkers might be affected not only by your own medical problems, but also by genetics, geographic location and other things,” she said. “Just because a test was developed in one location doesn’t mean it’s going to have the same sensitivity or specificity in another location. That is really important to highlight.”

How can I get a blood test for Alzheimer’s disease?

Access to the new blood tests for Alzheimer’s varies depending on the test. For example, the PrecivityAD2 test is available only with a physician’s order. An individual can get Quest’s AD-Detect test for beta-amyloids without a doctor’s order, Carlisle said. However, she added an important caveat.

“This type of screening tool should only be used by physicians or other providers who really understand the value of the result,” Carlisle said.

Why should people be cautious about getting the blood tests without consulting with a doctor?

Test results and additional information may be helpful to some individuals and family members. But Carlisle warns people that the new blood tests for Alzheimer’s can return false negative or positive results. Plus, it’s vital to have help understanding and interpreting the results.

“It’s important to know what to do with the information and how to counsel the patient about it,” Carlisle said.

Experts at the Alzheimer’s Association bolster that view, saying, “at this time, it is recommended that blood tests only be used by specialty care doctors who are seeing patients with memory complaints.”

Are the tests covered by insurance?

No. None of the new blood tests for Alzheimer’s are fully approved by the Food and Drug Administration (FDA), and they are not currently covered by Medicare, Medicaid or private insurance, Carlisle said. For now, patients likely will have to pay out of pocket for any of the available tests. However, some tests, including the Elecsys pTau217 from Roche Diagnostics and the Simoa phospho-Tau 217 from AlzPath, have received “breakthrough device designations” from the FDA, which could speed their approval.

How much should I expect to pay out of pocket for a blood test for Alzheimer’s disease?

The costs vary by hundreds of dollars, as this analysis from early 2024 shows. The AD-Detect test lists for $399. The PrecivityAD2 test — which demonstrated promise in the clinical trial noted earlier — costs $1,450, Carlisle said. The manufacturer, C2N Diagnostics, offers patient assistance to those who qualify, she added, “but that’s still potentially a pretty high cost.”

How soon will the new blood tests for Alzheimer’s be widely available?

Carlisle speculated that it could be 5 to 10 years before the new blood tests for Alzheimer’s are widely available. However, the move in dementia care toward early detection might speed that up. For example, the United States Preventive Services Task Force (USPSTF) does not formally recommend cognitive screening for older patients, unless they express concerns about memory loss or other symptoms. Why? Because until recently, providers have had few options to treat people with Alzheimer’s disease. But with the FDA approval of anti-amyloid therapies Leqembi (lecanemab) and Kisunla (donanemab), that is changing, and USPSTF experts could convene again soon to review and modify their recommendations, Carlisle said.

“In the future, I think we are going to start trying to identify patients sooner, which means you would have to do a universal screening,” she said.

Early screening for Alzheimer’s would start with a comprehensive battery of cognitive tests, “but perhaps the next step would be something like a biomarker test to understand how much we really need to be worried about (an individual’s symptoms).”

I’ve decided to pay for a blood test. What are some of the issues I should consider?

First, any test for Alzheimer’s disease should only be done if you are exhibiting measurable signs of cognitive impairment, such as memory problems, Carlisle said.

“There are typical changes in thinking that occur with aging and medical problems, so it is important to have a medical provider involved,” she stressed.

Second, at least for now, a blood test can be used to screen for Alzheimer’s disease, but these results are not yet considered a definitive diagnosis, Carlisle said.

“We have no promises from insurance companies — including Medicare and Medicaid — whether or not a blood-based biomarker would be considered confirmation of Alzheimer’s or if we would need to then do a gold standard (test),” Carlisle said. “If you are doing a screening and then it’s positive, we still have to do a lumbar puncture or an amyloid PET scan. That is something we have to consider.”

Third, not all Alzheimer’s disease blood tests are the same. For example, tests that measure p-tau217 are generally more sensitive than those that measure the ratio of beta-amyloid 42 and 40 alone, Carlisle said. As she noted, the PrecivityAD2 test uses both measures.

Isn’t it worth it if a simple blood test can give me answers about my risk of getting Alzheimer’s disease?

There isn’t a straightforward answer to whether it’s worth it for most people to take the new blood tests for Alzheimer’s so they can get answers about their risks for getting Alzheimer’s, Carlisle said.

Even if a blood test reveals the amyloid and tau culprits of Alzheimer’s disease, the findings do not predict how the condition will affect an individual, Carlisle said. A person should weigh the potential benefits of getting additional information against the potential harms — including anxiety and distress — that learning about signs of Alzheimer’s could cause for individuals and loved ones, she said.

Signs of cognitive decline may not be attributable to Alzheimer’s disease, Carlisle noted.

For example, an individual might experience memory loss with no clear start date that progresses slowly over time. In that case, “the suspicion for Alzheimer’s is going to be higher,” she said. “But that doesn’t mean that (Alzheimer’s) is actually the pathology that is causing the problem,” Carlisle continued.

For example, limbic-predominant age-related TDP-43 encephalopathy (LATE) causes short-term memory loss, thinking problems and other symptoms that mimic Alzheimer’s disease. However, it is not associated with amyloid, but rather a defect in the TDP-43 protein that causes deposits in the brain that damage cognition. As of now, LATE can only be definitely diagnosed during an autopsy, she added.

“Even though a person in life and clinically looks like they have Alzheimer’s disease, it’s not always Alzheimer’s disease,” Carlisle said.

OK. If I need a lumbar puncture to test for Alzheimer’s disease, what does that entail? How painful, difficult or risky is a lumbar puncture?

A lumbar puncture is a pretty standard procedure that generally takes about 30 minutes after the setup. Some people may be uncomfortable having a large needle inserted in the lower back, but the procedure generally is not painful. Providers draw cerebrospinal fluid, which “bathes” the spinal cord and the brain, she said.

What can that cerebrospinal fluid tell us?

It may contain low levels of beta-amyloid, which is a sign that the proteins are getting stuck in the brain, and/or high levels of tau. In combination, these findings help to confirm a diagnosis of Alzheimer’s disease, Carlisle said.

The fluid may contain clues to other diseases that affect cognition. For example, it may reveal signs of inflammation, such as specific antibodies, like the anti-NMDA antibody. That antibody causes anti-NMDA receptor encephalitis, which includes symptoms of cognitive decline, Carlisle said.

Other tests of the fluid can help providers diagnose diseases like Creutzfeldt-Jakob disease that also deteriorate memory and thinking, she noted. An alpha-synuclein seed test of cerebrospinal fluid could also help to diagnose dementia with Lewy bodies – another cause of cognitive impairment – but this test is not yet covered by insurance, Carlisle said.

Are there advantages to a lumbar puncture over an amyloid PET scan in testing for Alzheimer’s disease?

Yes. A lumbar puncture can help to rule in or out autoimmune diseases, like anti-NMDA receptor encephalitis, or other neurodegenerative disorders, like Creutzfeldt-Jakob disease, mentioned above, Carlisle said. That’s particularly important for younger people with early-onset cognitive decline because their risk of Alzheimer’s disease is relatively low.

For people considering the anti-amyloid therapies lecanemab and donanemab, Carlisle also prefers a lumbar puncture. “The amyloid PET scan tells me only about amyloid,” she said. “It doesn’t tell me anything about other markers we see in Alzheimer’s disease, like tau.”

Carlisle added that in the two clinical trials that led to the approval of these drugs, people with higher levels of tau were less likely to respond to the treatments. “The information about tau can be helpful, but we can’t get it with PET imaging,” Carlisle said.

In summary, how do you assess, as of today, blood tests to screen for Alzheimer’s disease?

“My best advice is that just because it might be easy to get one of these tests, it doesn’t mean you will be able to interpret the results in a meaningful way,” Carlisle said. “I highly recommend that people talk to their primary care provider, and if there are concerns about their cognition, that they see a [neurology] and/or dementia specialist in their area and determine what the proper workup would be.”