Tests for Tau protein and Aß42 may be used as supplemental tests to help establish a diagnosis of Alzheimer disease and to distinguish between AD and other forms of dementia. These tests are not widely used or routinely ordered. Use is limited to those suspected of dementia, and testing is typically performed after other causes of a person's symptoms have been ruled out.
Tau protein and Aß42 tests are primarily performed in research settings and in some memory clinics in conjunction with cognitive tests and brain scans when someone has symptoms of dementia, such as memory loss, behavioral changes, and decreased ability to perform daily life functions. Some health practitioners may order them outside of these settings; however, information on how to interpret the results is limited.
In a symptomatic person, a low Aß42 CSF level along with a high tau level reflects an increased likelihood of Alzheimer 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.
Assessments of Aß42 and tau protein levels do not singularly establish a diagnosis of Alzheimer disease; they represent a common finding that may be used in conjunction with other tests and the person'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.
If someone has symptoms of dementia, a health 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 (Pittsburgh Compound-B) of the brain to look for abnormalities.
This article was last reviewed on March 14, 2014. | This article was last modified on December 29, 2014.
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