Blood Tests for Alzheimer’s: A Complex Decision
The concept is quite simple: have a blood test now, even if you’re showing no symptoms, to see if you may eventually develop Alzheimer’s disease. But the question of whether you actually should get this test? That’s where things get a bit murky.
Most Alzheimer’s blood tests focus on measuring levels of amyloid or tau, proteins that accumulate in the brain and are believed to play significant roles in the illness. These proteins can start building up decades before any signs of the disease show.
However, there’s still ongoing debate about the reliability of these tests in predicting who will later develop Alzheimer’s disease. Some individuals who test positive for these markers never go on to develop the disease, which raises questions about the trustworthiness of the results.
Even if the tests can accurately gauge risk, a bigger issue arises: what should patients do with that information? With no cure for Alzheimer’s, which affects roughly 7 million people in the U.S., according to Mayo Clinic, the approved medications—Leqembi and Kisunla—aim to slow the condition rather than cure it. There’s mixed evidence on their effectiveness, and they come with serious potential side effects, like brain swelling and bleeding. While diet and exercise might reduce Alzheimer’s risk, their impact is rather limited.
Dr. Alberto Espay, a neurologist at the University of Cincinnati College of Medicine, emphasizes the challenge here. “The idea behind early disease testing is that if we act sooner, the results will improve,” he said. “Yet, there’s no proof that those at the earliest stages would actually benefit from what we currently have.”
This dilemma is echoed in a recent survey published in the journal Alzheimer’s & Dementia, revealing that 85% of patients would opt for a blood test to check their risk if recommended by their doctor.
The survey gathered responses from nearly 600 adults, averaging 62 years of age, at primary care clinics in Chicago. About half had a family history of Alzheimer’s, although none were diagnosed, and most hadn’t previously heard of the tests.
The lead author, Andrea Russell, noted that the findings reflect a common anxiety among older patients. “There seems to be a strong desire for people to understand their health status,” she said. Interestingly, nearly three-quarters of participants indicated they would feel distressed if their test results were positive, even while most also mentioned they would likely take steps to enhance their brain health.
As a psychologist, Russell doesn’t prescribe these tests but questions their validity. “There are still many uncertainties. They’re not quite ready for widespread use,” she stated. “Skepticism definitely exists.”
The FDA has approved two blood tests for Alzheimer’s in the past year, intended for individuals aged 55 and older showing symptoms, but not for asymptomatic individuals. These tests don’t function as standalone diagnoses and must be used in conjunction with other assessments, like PET scans. The FDA also mentioned that the main risk associated with these tests is the potential for inaccurate results, which might lead to inappropriate diagnoses and unnecessary treatments.
Despite these limitations, there are at least 25 blood tests available globally, with more in the pipeline, according to the Alzheimer’s Association, which advocates for testing.
Rebecca Edelmayer, the Alzheimer’s Association’s vice president of scientific engagement, stresses that the approval of these tests is crucial—not only for early diagnosis but also for ensuring patients can access diagnoses easily. These tests are easier to conduct, reasonably priced, and far more convenient than PET scans or MRIs.
“Public opinion strongly favors early Alzheimer’s diagnosis and treatment,” Edelmayer commented in a statement. “People want to know if they’re experiencing Alzheimer’s or another dementing condition before it significantly affects their daily lives.”
Dr. Ronald Petersen from the Mayo Clinic noted that blood tests have improved significantly but still require further refinement. He indicated that these tests are generally utilized in three primary ways.
First is as a predictive tool, estimating the likelihood of amyloid presence in the brain, which is then usually verified via a PET scan. Secondly, they can track treatment progress; ideally, doctors could use these tests over time to monitor amyloid levels or other changes following the initiation of an Alzheimer’s medication. The third role is in diagnosis—determining whether a blood test alone can confirm Alzheimer’s by identifying amyloid or other disease markers in the brain.
However, Petersen remains cautious. “I think we’re still figuring this out,” he remarked. “Some people may feel satisfied with a blood test result, but inconsistencies between blood tests and imaging methods have led many experts to remain skeptical of using blood tests as the sole diagnostic tool.”
A 2024 study found that blood tests accurately identified Alzheimer’s in patients with memory issues approximately 90% of the time. Yet, experts pointed out that since the study was done in Sweden, it needs validation in the more diverse U.S. population. In December, the Mayo Clinic presented data suggesting that one of the FDA-approved blood tests might be overly sensitive, often flagging patients as positive more frequently than other diagnostic methods.
Espay warned that amyloid and tau are also found in the brains of some older adults who may never develop the disease. “It might not mean you’re sick,” he explained. “As we age, our brains develop certain pathologies, but very few people will ultimately die from the diseases we associate with those changes.”
Petersen remains optimistic that these tests could evolve into standalone diagnostic tools in the future, although the field hasn’t reached that point yet.
Russell believes that many patients are eager to discern if their experiences are typical for aging or indicative of something more serious. “Having that clarity could offer a sense of hope and control,” she remarked.
