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.
The Test Sample
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.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
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.
The Test
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.
Common Questions
Ask a Laboratory Scientist
This form enables you to ask specific questions about your tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. If your questions are not related to your lab tests, please submit them via our Contact Us form. Thank you.
* indicates a required field
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
(Updated 2008 December 15) Alzheimer's Disease. CDC Features [On-line information]. Available online at http://www.cdc.gov/Features/Alzheimers/ through http://www.cdc.gov. Accessed February 2009.
(Updated 2009 February 5) Understanding Stages and Symptoms of Alzheimer's Disease. National Institute on Aging [On-line information]. Available online at http://www.nia.nih.gov/NR/exeres/6739F4B3-C1A9-4564-8AC3-77DC1315974E.htm through http://www.nia.nih.gov. Accessed February 2009.
Welsh-Bohmer, K. and White, C. (Current 2009 February 17) Alzheimer disease: What changes in the brain cause dementia? American Academy of Neurology 2009;72:e21 [On-line information]. Available online at http://www.neurology.org/cgi/content/full/72/4/e21?maxtoshow=&HITS=20&hits=20&RESULTFORMAT=&searchid=1&FIRSTINDEX=0&displaysectionid=Patient+Pages&resourcetype=HWCIT through http://www.neurology.org. Accessed February 2009.
Rodgers, A. (Updated 2008 November 28) Alzheimer's Disease: Unraveling the Mystery. National Institute on Aging, ADEAR [On-line information]. Available online at http://www.nia.nih.gov/Alzheimers/Publications/Unraveling/ through http://www.nia.nih.gov. Accessed February 2009.
Portelius, E. et. al. (2008 June 20) Targeted Proteomics in Alzheimer's Disease: Focus on Amyloid-Beta. Medscape.com from Expert Rev Proteomics 2008;5(2):225-237 [On-line information]. Available online at http://www.medscape.com/viewarticle/575519 through http://www.medscape.com. Accessed February 2009.
Yaari, R. and Corey-Bloom, J. (2007 March 07). Alzheimer's Disease. Medscape.com from Seminars in Neurology Semin Neurol 2007;27(1):32-41 [On-line information]. Available online at http://www.medscape.com/viewarticle/553256 through http://www.medscape.com. Accessed February 2009.
Harrison's Principles of Internal Medicine. 16th ed. Kasper D, Braunwald E, Fauci A, Hauser S, Longo D, Jameson JL, eds. McGraw-Hill, 2005, P. 2399.
Tapiola T, Alafuzoff I, Sanna-Kaisa, et. Al: Cerebrospinal fluid B-amyloid 42 and tau proteins as biomarkers of Alzheimer-type pathologic changes in the brain. Arch Neurol 66(3):382-389, 2009.
Snider BJ, Fagan AM, Roe, C, et. Al: Cerebrospinal fluid biomarkers and rate of cognitive decline in very mild dementia of Alzheimer type. Arch Neurol 66(5):638-645, 2009.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
Sloane, P. (1998, November 1). Advances in the Treatment of Alzheimer's Disease. American Family Physician by the American Academy of Family Physicians [On-line journal]. Available online at http://www.aafp.org/afp/981101ap/sloane.html through http://www.aafp.org.
Eastman, P. (2002 March). Keeping Alzheimer's at Bay, Early Diagnosis Keeps Patients Functioning Longer. AARP Bulletin Online [On-line serial]. Available online at http://www.aarp.org/bulletin/departments/2002/health/0310_health_1.html through http://www.aarp.org.
McConnell, S. , et. al. Unraveling the Mysteries of Alzheimer's Disease: Exciting New Developments in Research. From panel sponsored by the Alzheimer's Association [On-line information]. Available online at http://www.asaging.org/am/cia2/alzheimer.html through http://www.asaging.org.
Galasko, D., et. al. (1998). High Cerebrospinal Fluid Tau and Low Amyloid b42 Levels in the Clinical Diagnosis of Alzheimer Disease and Relation to Apolipoprotein E Genotype. Arch Neurol [On-line journal], vol (55) pages (937-945). Available online at http://archneur.ama-assn.org/issues/v55n7/abs/noc7433.html through http://archneur.ama-assn.org.
ARF (1996-2002). Standard Medical Workup for Alzheimer's Disease. Alzheimer Research Forum [On-line information]. Available online at http://www.alzforum.org/members/research/treatment_guide/workup.html through http://www.alzforum.org.
Family Caregiver Alliance. Fact Sheet: Alzheimer's Disease [On-line information]. Available online at http://www.caregiver.org/factsheets/diagnoses/alzheimersC.html through http://www.caregiver.org.
Bird, T. (2001 June 22 last update). Alzheimer Overview. GeneReviews [On-line information]. Available online through http://www.genetests.org.
Gottlieb, F. and Lambert, J. G. (2002, January 2, last update). Alzheimer's Disease. MEDLINEplus [On-line information]. Available online at "http://www.nlm.nih.gov/medlineplus/ency/article/000760.htm">http://www.nlm.nih.gov/medlineplus/ency/article/000760.htm.
Miller, M. (1998 February 18). 26 national Alzheimer's Disease Centers Collaborate on Study of the Utility of Genetic Testing for Alzheimer's. National Institutes of Health News Release [On-line press release]. Available online at http://www.nia.nih.gov/news/pr/1998/02%2D18.htm through http://www.nia.nih.gov.
NIH (2000). Progress report on Alzheimer's disease, taking the next steps. NIH Publication No. 00-4859 [On-line report]. Available online at http://www.alzheimers.org/pubs/prog00.htm#Introduction through http://www.alzheimers.org.
UniSci (2002, April 08). New Approaches Seen For Early Alzheimer's Diagnosis. Daily University Science News [On-line Article]. Available online at http://unisci.com/stories/20022/0408025.htm through http://unisci.com.
Eldercare (2002 February 28, last update). Is it Alzheimer's ... or Just Forgetfulness? Sponsored by Nebraska's Area Agencies on Aging [On-line information]. Available online at http://nncf.unl.edu/eldercare/info/lifeline/LLforget.html through http://nncf.unl.edu.
Diagnostic Education, Neurological Disorders, Alzheimer's Disease. Athena Diagnostics [On-line information]. Available online at http://www.athenadiagnostics.com/site/content/neuro_alzheim_dis.asp through http://www.athenadiagnostics.com.
NeuroCast. Neuropathology of Alzheimer's Disease. Athena Diagnostics [On-line information]. Available online at http://www.neurocast.com/site/content/sessions_Neuro_Alzheimer's.shtml through http://www.neurocast.com.
NeuroCast. Biochemistry of Alzheimer's Disease. Athena Diagnostics [On-line information]. Available online at http://www.neurocast.com/site/content/sessions_Biochemistry_Alzheimer's.shtml through http://www.neurocast.com.
Hain, T. (2000 February 13). Alzheimer's Disease. Neurology, Northwestern University Medical School. Available online at http://www.neuro.nwu.edu/meded/behavioral/alzheimers.html through http://www.neuro.nwu.edu.
Kleiner-Fisman, G., Updated by (2002 January 2, last update). CSF Collection. MEDLINEplus [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003428.htm.
Lawrence Mayer, MD, PhD. Professor, Department of Psychiatry and Behavioral Sciences, Johns Hopkins School of Medicine, Baltimore, MD.
American Academy of Neurology guidelines on dementia: PDF available for download at http://www.aan.com/professionals/practice/pdfs/dementia_guideline.pdf through http://www.aan.com.
Sunderland, T et al. Decreased beta-amyloid1-42 and increased tau levels in cerebrospinal fluid of patients with Alzheimer disease. JAMA. 2003 Apr 23-30;289(16):2094-103. Available online at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=Display&DB=pubmed through http://www.ncbi.nlm.nih.gov.
Andreasen, Niels. Biochemical markers and diagnosis of Alzheimer's Disease. Alzheimer Insights Online, Vol. 7, No. 3. Available online at http://www.alzheimer-insights.com/insights/vol7no3/vol7no3b.htm through http://www.alzheimer-insights.com.
Alzheimer's Research at Mayo Clinic. 11/11/2003. Available online at http://mayoresearch.mayo.edu/mayo/research/Featured_Stories/alzheimers_disease/ through http://mayoresearch.mayo.edu.
