Também conhecido como
Alzheimer biomarkers
Nome formal
Tau protein and Amyloid Beta 42 peptide
Este artigo foi revisto pela última vez em
Este artigo foi modificado pela última vez em
11 de Janeiro de 2018.
At a Glance
Why Get Tested?
To help discriminate between Alzheimer's Disease and other forms of early-onset dementia
When To Get Tested?
These tests may be ordered along with cognitive and brain-imaging tests in patients who demonstrate some form of dementia. These tests are not routine laboratory tests and are available only in research settings or memory clinics.
Sample Required?
A sample of cerebrospinal fluid collected using a spinal tap
Test Preparation Needed?
Your doctor will advise you of any preparatory requirements.
What is being tested?
Amyloid beta 42 is a peptide that can undergo increased production resulting in a collection of senile plaques in the brain. Tau is a structural protein of the brain that, when changed chemically (becomes saturated with phosphorus groups, P-tau), can create neurofibrillary tangles, twisted protein fragments that develop in neurons that disrupt their ability to transport signals. These tangles in conjunction with the plaques are considered to be the main diagnostic features of Alzheimer's Disease (AD) at autopsy. The measurement of tau and Aß42 in CSF is being evaluated for potential roles in the diagnosis and monitoring of AD. It has been shown that a decrease in Aß42 with elevated tau or P-tau levels may predict the onset of AD.

How is the sample collected for testing?

Cerebrospinal fluid samples are collected using a lumbar puncture (spinal tap) procedure. This procedure is usually done in a hospital or clinic.

Is any test preparation needed to ensure the quality of the sample?

Your physician will advise you of any preparatory requirements. This is not a blood test but one on spinal fluid. Lumbar punctures are usually done in a hospital setting.
Accordion Title
Common Questions
  • How is it used?
    Tests for Tau protein and Aß42 may be used as supplemental tests to help establish a diagnosis of Alzheimer's Disease.

    If someone has symptoms of dementia, such as memory loss, behavioral changes, and decreased ability to perform daily life functions, the doctor will do a thorough work-up to try to determine the cause. This work-up may include a variety of cognitive tests (Minimal Mental State Exam) to assess memory and possibly PET scanning tests (Pittsburgh Compound-B) of the brain to look for abnormalities.

  • When is it ordered?
    Tau protein and Aß42 tests are primarily performed in research settings and in some memory clinics in conjunction with cognitive tests and brain scans. Some doctors may order them outside of these settings; however, information on how to interpret the results is limited.
  • What does the test result mean?
    In a symptomatic patient, a low Aß42 CSF level along with a high tau level reflects an increased likelihood of Alzheimer's Disease. Recent studies have shown that these abnormal levels may predict a rapid progression of AD. Since these are still in a research phase and not part of routine examinations, it is unclear as to whether all who might have abnormal results would definitely have AD.
  • Is there anything else I should know?
    Assessments of Aß42 and tau protein levels do not singularly establish a diagnosis of Alzheimer's Disease; they represent a common finding that may be used in conjunction with other tests and the patient's clinical and family history to suggest a diagnosis of AD.

    The clinical use of these tests continues to evolve. For instance, multiple variants of amyloid beta protein, such as Aß40 and Aß38, have been identified and are being researched for their potential use as AD biomarkers.

  • How is Alzheimer's Disease definitively diagnosed?
    Alzheimer's disease is currently diagnosed based on cognitive changes and by ruling out other causes of these changes. It 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 senile plaques and neurofibrillary tangles found in the brain. Characteristic changes on brain scans (MRI or PET scans) and/or low Aß42 and high tau protein levels in CSF (where available) may be ordered to help in the diagnosis.
  • Can I have my blood tested instead of my CSF?
    Not at this time. Studies of blood measurements of Aß42 and tau have not shown them to be useful reflections of what is occurring in a person's brain.
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