Also Known As
Alzheimer Biomarkers
Formal Name
Tau Protein and Amyloid Beta 42 Peptide
This article was last reviewed on
This article waslast modified on February 6, 2020.
At a Glance
Why Get Tested?

To help distinguish between Alzheimer disease and other forms of dementia

When To Get Tested?

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.

Sample Required?

A sample of cerebrospinal fluid collected using a lumbar puncture (spinal tap)

Test Preparation Needed?

Your healthcare practitioner will advise you on how you need to prepare for the test.

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

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.

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Common Questions
  • How is the test 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?

    In a person with symptoms, a low beta amyloid CSF level along with a high tau protein level reflects an increased likelihood of Alzheimer disease. However, these abnormal results can also occur in other conditions.

  • 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?

    Not at this time. Studies of blood measurements of beta amyloid and tau have not shown them to be useful in determining what is occurring in a person's brain.

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Elsewhere On The Web

National Institute on Aging: Alzheimer Disease & Related Dementias
Centers for Disease Control and Prevention: Alzheimer Disease
Alzheimers Association
View Sources

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