Taking a test to see if you or a loved one might have Alzheimer’s might sound nerve-wracking, but early detection means you can start treatments that can slow the disease's progression. In the past, the neurogenerative disease could only be accurately diagnosed once people had already died, but scientific advancements now allow doctors to diagnose the condition much earlier, using a slew of tools including blood tests. It's important to note that there isn't one single test that can diagnose the disease. Rather, doctors use neurological exams, cognitive and functional tests, brain imaging and cerebrospinal fluid or blood tests to make diagnoses, per the Alzheimer's Association.
But there's a catch: New research suggests that those blood tests may be unreliable, especially in Black patients. Doctors who treat people with Alzheimer’s disease say there are a lot of flaws with these blood tests, and this is just one more to keep in mind. Here’s what experts want you to know.
Meet the experts:Clifford Segil, DO, a neurologist at Providence Saint John’s Health Center in Santa Monica, CA; Amit Sachdev, MD, MS, medical director in the Department of Neurology at Michigan State University; Jennifer Bramen, PhD, senior research scientist and director of neuroimaging at the Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA; William Hu, MD, study co-author and associate professor and chief of cognitive neurology and the Alzheimer’s Disease Clinic at the Rutgers Institute for Health
What did the study find?
The study, which was published in the journal Alzheimer’s & Dementia, analyzed test results from 221 people who underwent in-depth evaluations, including blood and spinal fluid tests and brain imaging, to look for the presence of Alzheimer’s disease.
The researchers used automated testing systems to look for levels of proteins, including p-Tau217 (a protein that plays a role in Alzheimer’s disease), in the blood and spinal fluid samples.
The scientists discovered that there was a 70 percent correlation between the protein levels in the blood and spinal fluid samples, but there were clear racial disparities in the accuracy of the results. When researchers looked for p-Tau217 in the blood to detect Alzheimer’s disease, there was a 90.3 percent chance of diagnosing patients with the disease and an 81.1 percent chance of correctly identifying someone as not having the disease in white participants. But in Black participants, those numbers dropped to 73.7 percent and 72.5 percent, respectively.
The chance of having the disease with a positive test was also significantly higher in white participants (87 percent) compared to Black participants (58 percent).
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How much are the blood tests?
These blood tests are not cheap: They can cost between $1,200 to $2,000 and are usually not covered by insurance, according to William Hu, MD, study co-author and associate professor and chief of cognitive neurology and the Alzheimer’s Disease Clinic at the Rutgers Institute for Health.
So, if they're not always reliable, that's a pretty big deal.
Why are the blood tests unreliable?
It's not just that they tests seem to have racial disparities. There are also other factors that make them unreliable. And that's due to a mix of biological and technical factors at play, Dr. Hu says. “The blood test itself measures the protein well, but there are many biological factors which influence concentrations of the protein measured by this and other similar tests that their interpretation is not straightforward,” he explains. “As such, a physician would need to very skillfully work backwards to properly translate the results.”
He gives this example: The protein p-Tau217 increases when a person’s Alzheimer’s disease is more severe and when someone has kidney disease, so a doctor would need to factor in how much memory dysfunction someone has and their kidney function.
Why are there racial disparities?
It's not clear at this point why the test is less accurate in detecting Alzheimer's in Black participants. “The why remains a mystery,” Dr. Hu says. “We knew from 10 years ago that racial disparities existed in the spinal fluid version of similar tests (total tau and p-Tau181), and this extends to other tau-related brain changes, so it is not an isolated finding.”
Dr. Hu has a theory, though: “I suspect what happens in the brain after formation of the Alzheimer’s plaques differs between individuals, and the relative proportion of people having one type of response versus another must vary according to race or ancestry.”
When will there be more accurate tests?
It's important to note that doctors who treat patients with Alzheimer’s say that these blood tests aren’t really considered the gold standard of diagnostic tools to start with.
“Using blood tests to diagnose Alzheimer’s dementia remains controversial in the clinical practice of neurology,” says Clifford Segil, DO, a neurologist at Providence Saint John’s Health Center in Santa Monica, CA. These tests “have a high number of false positives,” he says, noting that some patients with “dementia” biomarkers have no memory loss.
“Blood tests to diagnose dementia remain unreliable as biomarkers are often wrong,” Dr. Segil says. However, he points out that “blood tests continue to be used to rule out reversible causes of memory loss, like low abnormal thyroid labs.”
But things are improving quickly in Alzheimer’s research, according to Jennifer Bramen, PhD, senior research scientist and director of neuroimaging at the Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA. “The field is moving fast, and we are seeing continuous improvements in blood-based biomarkers,” she says. “In the coming years, we expect tests to become more refined, with better ways to account for individual differences.”
Are there any other ways to test for Alzheimer’s?
As mentioned earlier, diagnosing Alzheimer’s disease can be pretty complex, and it’s often best to look at several different diagnostic tools, says Amit Sachdev, MD, MS, medical director in the Department of Neurology at Michigan State University.
“The most important thing to recall is that we never rely on a single test to tell a story in medicine,” he says. “This is especially true in neurology. If I were diagnosing dementia, I would rely on the patient telling me about their symptoms, then I would take pictures of the brain and I would get blood work. Blood work would include several measures of brain health, not just one.”
From there, Dr. Sachdev says he would ask the patient to consider memory testing if the results were unclear, along with a spinal tap.
“We never rely on a single test because genetics and lived experience is so different,” Dr. Sachdev says. “We will learn in time better ways to interpret each individual test, but I doubt we will ever rely on one test to tell a whole story.”
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Korin Miller is a freelance writer specializing in general wellness, sexual health and relationships, and lifestyle trends, with work appearing in Men’s Health, Women’s Health, Self, Glamour, and more. She has a master’s degree from American University, lives by the beach, and hopes to own a teacup pig and taco truck one day.