In this post, we break down everything you need to know about blood tests for Alzheimer’s disease, why they are important, and what information we still need before these tests will be ready for prime time in the U.S.
You may have seen news this summer about a highly accurate blood test for Alzheimer’s disease. In a research study , a blood test detected Alzheimer’s disease correctly in people with changes in memory and thinking around 90% of the time. In this post, we break down everything you need to know about blood tests for Alzheimer’s disease, why they are important, and what information we still need before these tests will be ready for prime time in the U.S.
What does the blood test look for?
As we outlined in our previous post, Alzheimer’s disease is one of the most common causes of dementia. Dementia is an overarching term for changes in memory and thinking that impact how a person functions. Alzheimer’s disease occurs when specific proteins in the brain become misfolded, impairing brain cell function. Now, there are several blood tests being tested that can identify the two major proteins that become misfolded in Alzheimer’s disease – amyloid and tau. The blood test from this study combined two tests that look for both amyloid and tau to increase accuracy.
Why is it important to have blood tests?
🔶 Alzheimer’s disease is difficult to diagnose. It’s hard to see what’s going on in the brain. In fact, clinicians misdiagnose people who have Alzheimer’s disease about 25-40% of the time. Clinicians use information from the person with memory changes and someone who knows them well, neurological examinations, and tests to give people an accurate diagnosis. Adding objective tests, like s blood test, improves clinician’s ability to diagnose Alzheimer’s disease accurately.
🔶 Current tests are expensive, invasive, or time intensive. There are some current tests that increase diagnostic accuracy for Alzheimer’s disease.
🔹 Positron Emission Tomography (PET) scan – In a PET scan, clinicians inject a tracer into a person’s blood and scan the brain. The tracer highlights the proteins that are misfolded in Alzheimer’s disease and they show up on an image of the brain. This scan increases clinician’s accuracy when they diagnose Alzheimer’s disease. But it is expensive and not always covered by insurance.
🔹 Lumbar puncture (or spinal tap) – During a lumbar puncture, a clinician numbs an area around the lower spine and inserts a long needle between the vertebrae to drain a small amount of the fluid that surrounds the brain. Then a lab test identifies the Alzheimer’s proteins in the spinal fluid. The results of this test improve the accuracy of diagnosing Alzheimer’s disease, and it is considered the gold standard. This procedure is usually well tolerated but is more invasive and has potential side effects, such as headache or a spinal fluid leak.
🔹 Neuropsychiatric testing – During neuropsychiatric testing, a clinician, usually a neuropsychologist, completes many tests to challenge a person’s memory and thinking. These tests help identify changes that could occur in Alzheimer’s disease. However, this testing takes a long time (often many hours), can be expensive, and there are not many providers who can do it, especially in rural areas.
In comparison to these options, a blood test is relatively cheap, non-invasive, and quick!
🔶 Blood tests could help to identify who could benefit from medications. There are now two drugs approved to treat Alzheimer’s disease in the U.S. These drugs are currently only approved for people who have known Alzheimer’s disease. They work best at the earliest stages of disease, when a person has no or minimal functional losses. But they have significant side effects, like bleeding in the brain. In order to identify people who could benefit from these medications, it’s important for healthcare providers to be able to accurately identify people with Alzheimer’s type dementia early in the disease process. Stay tuned for a post on these drugs next month!
What needs to happen before blood tests for Alzheimer’s disease would be available in clinics?
🔶 Scientists need data on the predictive accuracy of these tests in broader populations, including people with atypical forms of dementia, like frontotemporal dementia and Lewy Body dementia, and minoritized racial and ethnic groups.
🔶 Currently, the blood test requires special equipment that is not available in most commercial labs. This could make the test more expensive than other blood tests and insurers may not cover the cost.
🔶 We are not sure how accurate the blood test is in people without any changes in memory or thinking. Also, we are not yet sure how to interpret a positive result in this population.
🔶 Finally, the blood test would need to be approved by the U.S. Food and Drug Administration (FDA) and reviewed for coverage by the Centers for Medicare & Medicaid Services (CMS) in order to become available in clinics across the U.S.
For now, the new study is promising, but we need more research before these tests are ready for clinics in the U.S. Even then, only certain people should get this test. Stay tuned for any new science on Alzheimer’s disease blood test as it develops.
Be well,
Those Nerdy Girls
