When memory problems begin, one of the hardest questions for patients and families is whether they reflect normal aging or the early stages of Alzheimer’s disease. For decades, confirming Alzheimer’s disease meant a spinal tap or an expensive brain scan.
Now, a simple blood draw—the kind used for routine checkups—can flag the disease’s telltale signs, years before memory loss ever appears.
“Early detection of Alzheimer’s disease can provide access to disease-modifying therapies, such as amyloid-targeting treatments currently available only for mild cognitive impairment or mild dementia due to Alzheimer’s disease,” Dr. Jennifer Pauldurai, neurologist and medical director for the Brain Health and Memory Disorders program at Inova, told The Epoch Times.
However, the same experts who welcome the tests are urging caution about who should get one, and why.
What the New Blood Tests Measure
The tests look for biomarkers—proteins in the blood that signal changes happening inside the brain, including:
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Amyloid-beta: A protein whose abnormal buildup in the brain can be reflected in measurable changes in the blood. Amyloid plaques can begin building up in the brain 20 years or more before memory problems appear. Though the amyloid-beta theory has been challenged in recent years, it is still used as a key biomarker.
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Tau: A protein that helps support nerve cells. In Alzheimer’s disease, abnormal forms of tau can accumulate and form tangles inside the brain.
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Phosphorylated Tau (p-tau): Modified forms of tau that are closely linked to Alzheimer’s-related brain changes. Different blood tests measure modified forms of the tau protein, often named according to the site of change, such as p-tau181 or p-tau217. Research suggests that p-tau217 may be one of the most accurate indicators of the disease.
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Glial Fibrillary Acidic Protein: A marker of inflammation in the brain’s support cells.
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Neurofilament Light Chain: A protein released when nerve cells are damaged, which may indicate ongoing neurodegeneration.
Still, researchers caution these markers capture downstream effects, not root causes.
“We do not yet know what the earliest change in Alzheimer’s disease is,” George Perry, a professor of neurobiology at The University of Texas at San Antonio and editor-in-chief of the Journal of Alzheimer’s Disease, told The Epoch Times.
Tau helps identify Alzheimer’s-related brain changes in people who are already showing cognitive symptoms, Perry said. However, researchers believe the disease begins with other biological changes, such as oxidative stress and mitochondrial dysfunction, for which reliable biomarkers have not yet been established, he added.
How Accurate Are the Tests?
By measuring subtle changes in proteins such as p-tau217 and amyloid-beta, newer blood tests can estimate whether the brain has markers of Alzheimer’s.
These figures, however, should not be interpreted as meaning that every Alzheimer’s blood test is 95 percent accurate. Performance varies depending on what the test is looking for, the type of lab test, the threshold used to determine a positive or negative result, and who the patient is.
Blood tests are increasingly being used in primary care as an early screening tool for possible Alzheimer’s-related changes, especially given long wait times for neurology appointments, Pauldurai said. These tests may also help distinguish Alzheimer’s from other causes of memory loss and, in some cases, be used to monitor response to treatment over time, she said.
A Positive Test Doesn’t Tell the Whole Story
Despite the accuracy of the figures, experts agree that a blood test alone cannot diagnose Alzheimer’s.
The biggest concern is misinterpretation, Dr. David Perlmutter, a board-certified neurologist and author, told The Epoch Times.
“A false positive may cause unnecessary fear, while a false negative may provide false reassurance. These tests should be used with counseling and clinical context,” Perlmutter said.
Perry drew a comparison to a familiar, and famously imperfect, screening tool: “I see Alzheimer’s disease blood tests much like the PSA [prostate-specific antigen] test. A positive result indicates a departure from normal, but it does not necessarily mean a person has the disease.”
Blood tests could serve as a useful baseline measure, but their limitations need to be better understood, he said.
That’s why Perry cautions against using these tests to screen the general aging population. False positives could push cognitively healthy people toward unnecessary or risky treatments to prevent a disease they may not have or ever get. Their stronger near-term use may be in studying Alzheimer’s—defining patient populations and measuring the effectiveness of different treatments, he said.
These tests should be viewed as part of a broader clinical evaluation alongside symptoms, family history, cognitive testing, medications, sleep, mood, vascular risk, metabolic health markers, and possible causes of cognitive problems, Perlmutter said.
Depending on the blood test and symptom assessment, testing with cerebrospinal fluid or PET imaging may still be appropriate for confirmation.
What About People With No Memory Problems?
Researchers have known for years that biological changes associated with Alzheimer’s can begin long before obvious memory problems. Blood biomarkers may eventually make it possible to estimate an individual’s risk much earlier.
However, those numbers also illustrate why a biomarker may not be fate: Most people in the very-high group had not developed cognitive impairment within five years.
Researchers concluded that testing for p-tau217 could eventually contribute to individualized estimates of Alzheimer’s risk, while emphasizing that more testing in other populations is needed before such estimates can routinely guide care for those without symptoms of Alzheimer’s.
For now, these blood tests are not used unless a person shows symptoms of cognitive decline, in which case they’re used in conjunction with other diagnostic methods.
What Early Detection Can Change
For patients showing signs of cognitive decline, early diagnosis may create an opportunity for lifestyle changes that support brain health.
“A blood test is not destiny; it is information,” Perlmutter said. “The goal is not to predict the future, but to change it.”
