Tau Protein and Beta Amyloid
These tests may be ordered along with cognitive and brain-imaging tests in people who demonstrate some form of dementia. These tests are not routine laboratory tests and are typically available only in research settings or memory clinics.
Your healthcare practitioner will advise you on how you need to prepare for the test.
Two separate laboratory tests can measure amyloid beta 42 (beta amyloid) and tau protein in cerebrospinal fluid (CSF). These tests are often done at the same time to help evaluate an individual for Alzheimer disease (AD).
- Amyloid beta 42 is a peptide (protein fragment). Increased production of amyloid beta 42 in the brain can lead to the formation of amyloid plaques.
- Tau is a structural protein in the brain. Tau protein containing many phosphorus groups (P-tau) can produce neurofibrillary tangles, which are twisted protein fragments that develop in nerve cells and disrupt the cells' ability to transport signals.
Neurofibrillary tangles and amyloid plaques are considered to be the main diagnostic features of Alzheimer disease.
The measurements of tau and beta amyloid in CSF are being evaluated for potential roles in the diagnosis and monitoring of AD. It has been shown that a decrease in beta amyloid with elevated tau or P-tau levels may predict the onset of AD.
How is it used?
Lab tests for tau protein and beta amyloid may be used as supplemental tests to help evaluate a person suspected of having Alzheimer disease (AD) and to distinguish between AD and other forms of dementia. These tests are not widely used or routinely ordered. Use of these tests is limited to people suspected of having dementia, and testing is typically performed after other causes of a person's symptoms have been ruled out.
When is it ordered?
Tau protein and beta amyloid tests are primarily performed in research settings and in some memory clinics. The tests may be done along with cognitive tests and brain scans when an individual has signs and symptoms of Alzheimer disease, such as:
- Loss of memory that affects daily life—forgetting information that was recently learned. This can occur with normal aging, but the information is usually remembered later. This includes forgetting important dates or events, having to rely on memory aids, and asking for the same information again and again.
- Difficulty planning or problem solving, such as keeping track of bills and payments
- Problems completing usual tasks, such as forgetting how to get to a familiar location
- Confusion about place or time—losing track of time, forgetting where you are or how you got there
- Increasing difficulty reading or judging distances
- Problems speaking or writing—forgetting words, repeating the same thing, struggling with vocabulary
- Losing things more frequently and not being able to logically retrace steps to find them
- Impaired judgment, such as giving away unusually large amounts of money
- Increasing withdrawal from activities, including social, work or family events
- Changes in mood and personality, such as increasing anxiety, fear, suspicion and depression
Some healthcare practitioners may order these tests for other reasons; however, information on how to interpret the results outside of the settings described above is limited.
What does the test result mean?
Is there anything else I should know?
The clinical use of these tests continues to evolve. For instance, multiple variants of amyloid beta protein, such as amyloid beta 40 and amyloid beta 38, have been identified and are being researched for their potential use as AD biomarkers. Other CSF and blood tests for AD are also being researched.
What tests are usually done to evaluate a person for Alzheimer disease?
If someone has symptoms of dementia, a healthcare practitioner will do a thorough work-up to try to determine the cause. This work-up may include a variety of cognitive tests (such as a Minimal Mental State Exam) to assess memory and possibly PET scanning tests of the brain to look for abnormalities. Read the article on Alzheimer Disease for additional details.
How is Alzheimer disease definitively diagnosed?
Alzheimer disease is currently diagnosed based on cognitive changes and by ruling out other causes of these changes. The diagnosis is definitively confirmed after death by looking for microscopic changes in a person's brain tissue. The microscopic evaluation involves looking for the number of amyloid plaques and neurofibrillary tangles found in the brain. Characteristic changes on brain scans (MRI or PET scans) and/or low beta amyloid and high tau protein levels in CSF (where available) may be ordered to help establish a diagnosis.
Can I have my blood tested for beta amyloid and tau instead of my CSF?