Overview: New blood tests for Alzheimer’s disease have received a lot of hype, but they don’t simply predict or diagnose the disease. Biomarker tests are intended for those with signs and symptoms of cognitive decline, not for routine screening. Results should be interpreted by your neurologist along with other clinical information.
Alzheimer’s disease blood tests have garnered a lot of media attention and given rise to confusion and questions. What do the tests show? Do they really work? Who should get tested?
Affecting 6.9 million Americans, Alzheimer’s disease slowly destroys memory and thinking skills, and eventually, the ability to perform everyday tasks. It’s caused by damage to nerve cells in the brain. Blood tests detect biomarkers for Alzheimer’s disease, or abnormal brain deposits, by analyzing specific proteins in the blood.
The blood tests can’t diagnose Alzheimer’s on their own, however, and aren’t medically necessary for everyone. A neurologist or physician must order the test.
Heike Schmolck, MD, a neurologist from MercyOne Ruan Neurology Care, specializing in memory disorders like Alzheimer’s disease, answers your questions:
What do Alzheimer’s disease blood tests (AD biomarkers) measure?
“The blood tests detect whether an individual has abnormal levels of the protein Beta Amyloid in their brain that is the cause of Alzheimer’s disease. They cannot say whether someone has clinical Alzheimer’s disease,” Dr. Schmolck said.
How good are the blood tests?
“The only recommended blood test is called pTau 217. This one is very good at predicting Amyloid in the brain, but it is not perfect. There are other tests that do not reach the same diagnostic accuracy and thus should be avoided.”
What does a positive blood test mean?
Dr. Schmolck says it depends on the situation and gives this breakdown.
No memory symptoms: “In a person without memory symptoms, it is a risk factor for developing cognitive symptoms and Alzheimer's disease in the next decades. It does not mean they will ever develop symptoms, and the majority WILL NOT develop symptoms in the following 15 years. Testing for this group is not recommended.”
Mild age-related symptoms: “In a person with nonspecific symptoms, or mild age-related symptoms, this is more difficult to interpret. They could fall into the first group, or they could be exhibiting prodromal (early stage) Alzheimer’s disease. Testing for this group is not recommended.
Abnormal findings on cognitive tests: “In a person with abnormal findings on cognitive testing, the blood tests can be helpful. If there is a high suspicion for Alzheimer’s disease on exam, we skip the blood test as it is not needed. In cases that are less clear, the test can give us additional information. For example, we might confirm that a patient with a stroke and memory problems also has an Alzheimer’s disease component to their difficulties.
“Nevertheless, the test still cannot tell us whether Alzheimer’s disease is the driving problem for their symptoms. It is common for older patients to have two or three identifiable diseases in their brain, but not all of them are relevant. Alzheimer’s disease could be what is called a “co-pathology,” which means it is present but not the main disease process and likely not the cause of the symptoms.”
What does a negative blood test mean?
“If the blood test is negative, the person likely does not have Alzheimer’s disease changes in the brain,” Dr. Schmolck said. “That does not mean they do not have another brain disease that could cause memory problems.”
What’s the key takeaway?
“In summary, the test is helpful but there is too much hype around it,” Dr. Schmolck said. “We do not recommend the blood test be done without a more detailed cognitive evaluation by a specialist, as results are meaningless without a context, and can be difficult to interpret.”
Remember, the blood test itself does not diagnose Alzheimer’s disease, which has no cure. It’s one step in the diagnostic process. Your neurologist can help determine whether an Alzheimer’s disease blood test is medically necessary for your specific situation.
