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Diagnostic Tests for Alzheimer’s

Reviewed by: HU Medical Review Board | Last reviewed: January 2023

There are many different factors that go into an Alzheimer’s diagnosis. Alzheimer’s affects the brain, but it also impacts the rest of the body. And as doctors research the underlying biology and causes, different tests for Alzheimer’s have emerged as well.1-3

Your doctors will look at all of these tests together to determine if you have Alzheimer’s. Each test on its own is helpful. But together, they paint the most accurate picture of your cognitive (thinking) and physical health.

Genetic testing

Alzheimer’s is rarely a genetic disease. Genetic Alzheimer’s is an autosomal dominant disorder. This means that it can be inherited from just one parent.1

Nearly all genetic Alzheimer’s is early-onset. This means that instead of symptoms starting around age 65, symptoms can start as early as your 30s. There are 3 gene mutations (changes) responsible for early-onset genetic Alzheimer’s. These mutations are found in the genes:1,3

  • AAP on chromosome 21
  • PSEN 1 on chromosome 14
  • PSEN 2 on chromosome 1

Genetic testing in general is usually not necessary for diagnosing Alzheimer’s disease. However, in some cases of early onset Alzheimer’s it can be helpful. If a close family member has early-onset Alzheimer’s, it may be helpful to get tested. Genetic testing does not reveal if you are going to get Alzheimer’s, but it does let you see if you have one of those gene mutations.1,3

Imaging

Brain imaging can also be helpful in diagnosing and monitoring Alzheimer’s disease. There are a few types of brain imaging that are normally done:2,3

  • MRI (magnetic resonance imaging)
  • CT (computed tomography)
  • PET (positron emission tomography)

MRI uses radio waves and magnets to show a detailed view of your brain, while CT uses x-rays. PET uses a substance called a “tracer” to identify brain regions with more or less activity.2,3

Imaging alone is not enough to make a diagnosis. However, it is still a helpful part of the process. It can help rule out other causes for your symptoms, like stroke or a brain tumor. It can also distinguish between different types of brain diseases. Importantly, it can establish a baseline for future tests.1-3

Recently, a new type of imaging has emerged called “volumetric MRI.” This MRI scans the volume of different brain regions. Alzheimer’s disease has a specific pattern of degeneration (damage to the cells) that your doctors can see in these scans.1

Laboratory tests

There are many possible laboratory tests that can aid in an Alzheimer’s diagnosis. But the 2 main types are blood tests and cerebrospinal fluid (CSF) tests.2,3

Blood tests can help both to diagnose Alzheimer’s and to rule out other conditions, like thyroid issues. Doctors can look at the levels of tau or beta-amyloid, 2 markers of Alzheimer’s disease. They can also do a complete blood count, metabolic panel, and other more general tests.1-3

CSF tests can also be helpful. CSF is a colorless, watery fluid that flows around your spinal cord and brain to keep them protected.1-3

Your doctors can sample CSF through a minimally invasive procedure called a lumbar puncture (spinal tap). Research suggests that CSF may have markers of tau and beta-amyloid. There is also a marker called neurofilament light chain, which has been shown to be increased in people with Alzheimer’s disease.1-3

Each of these tests alone may not be conclusive. But when taken together, they can help doctors see an accurate picture of your brain and bodily health. If you are experiencing cognitive symptoms and believe you may have Alzheimer’s, talk to your care team about the best path forward.

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