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CD4 and CD8

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Also known as: T4 Count; T-helper Cells; T-suppressor Cells; Cytotoxic T-cells
Formal name: CD4 Lymphocyte Count; CD8 Lymphocyte Count; CD4/CD8 Ratio; CD4 Percent

At a Glance

Why Get Tested?

Most often, this test is done to measure the strength of your immune system if you have been diagnosed with human immunodeficiency virus (HIV) infection; occasionally, it may be used with other conditions (see Common Questions #4).

When to Get Tested?

When you have been diagnosed with HIV, soon after you are first diagnosed to get a baseline assessment of your immune system; 2-8 weeks after starting anti-HIV therapy and then every three to four months as you continue therapy

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

CD4 and CD8 cells are types of white blood cells that fight infection and play an important role in immune system function. They are made in the spleen, lymph nodes, and thymus gland, and they circulate throughout the body in the bloodstream. CD4 and CD8 cells have markers on the surfaces of the cells called clusters of differentiation (CD), and the number identifies the specific type of cell. CD4 and CD8 tests measure the number of these cells in the blood and, in conjunction with an HIV viral load test, help assess the status of the immune system in a person who has been diagnosed with human immunodeficiency virus (HIV).

CD4 cells are sometimes called T-helper cells. They help to identify, attack, and destroy specific bacteria, fungi, and viruses that affect the body. CD4 cells are a major target for HIV, which binds to the surface of CD4 cells, enters them, and either replicates immediately, killing the cells in the process, or remains in a resting state, replicating later. As HIV gets into the cells and replicates, the number of CD4 cells in the blood gradually declines. The CD4 count decreases with HIV disease progression. This process may continue for several years before the number of CD4 cells drops to a low enough level that symptoms associated with AIDS begin to appear. AIDS treatment reduces the amount of HIV present in the body and slows disease progression. When this occurs, the CD4 count will increase and/or stabilize.

CD8 cells are lymphocytes that are sometimes called T-suppressor cells or cytotoxic T cells. CD8 cells identify and kill cells that have been infected with viruses or that have been affected by cancer. They play an important role in the immune response to HIV by killing cells infected with the virus and by producing substances that block HIV replication.

As HIV disease progresses, the number of CD4 cells will decrease in relation to the number of total lymphocytes and CD8 cells. To provide a clearer picture of the condition of the immune system, the results of these tests may be expressed as a ratio of CD4 to total lymphocytes (percentage) or as a ratio of CD4 cells to CD8 cells.

CD4 and CD8 tests are most often used to help monitor disease progression in HIV but may also be used occasionally in other conditions, such as lymphomas and organ transplantation. (See Common Questions #4)

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

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?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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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

Anand, J. (Updated 2011 August 11). Antiretroviral Therapy in Treatment-Naive Patients. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2041458-overview through http://emedicine.medscape.com. Accessed February 2012.

Hughes, R. et. al. (2011 November 21). Long-term Trends in CD4 Cell Counts and Impact of Viral Failure in Individuals Starting Antiretroviral Therapy. Medscape Today from HIV Medicine v12 (10):583-593 [On-line information]. Available online at http://www.medscape.com/viewarticle/753337 through http://www.medscape.com. Accessed February 2012.

Bennett, N.J. and Gilroy, S. (Updated 2011 November 9) HIV Disease. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/211316-overview through http://emedicine.medscape.com. Accessed February 2012.

Bennett, N. (Updated 2011 July 14). Laboratory Assays in HIV Infection. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/1995114-overview#showall through http://emedicine.medscape.com. Accessed February 2012.

Dugdale, D. (Updated 2011 June 9). AIDS. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000594.htm. Accessed February 2012.

(© 1995–2012). Test ID: TCD4 CD4 Count for Immune Monitoring, Blood. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/84348 through http://www.mayomedicallaboratories.com. Accessed February 2012.

Hillyard, D. et. al. (Updated 2011 November). Human Immunodeficiency Virus - HIV. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/HIV.html?client_ID=LTD through http://www.arupconsult.com. Accessed February 2012.

(Revised 2011 March 10). CD4 (T-cell) Tests. AIDS InfoNet [On-line information]. Available online at http://aidsinfonet.org/fact_sheets/view/124 through http://aidsinfonet.org. Accessed February 2012.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 244-247.

Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 609-612.

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.

Janice K. Pinson MT, MBA. Molecular Business Strategies, Birmingham, MI.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 535-538.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp 487-490.

Bennett, N. and Rose, F. (2008 October 22, Updated). HIV Disease. eMedicine [On-line information]. Available online at http://www.emedicine.com/med/TOPIC24.HTM through http://www.emedicine.com. Accessed on 10/26/08.

Mayo Clinic Staff (2008 August 9). MayoClinic HIV/AIDS. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/hiv-aids/DS00005 through http://www.mayoclinic.com. Accessed on 10/30/08.

(2005 November, Revised). Human Immunodeficiency Virus (HIV) Introduction. Merck Manual for Healthcare Professionals [On-line information]. Available online at http://www.merck.com/mmpe/sec14/ch192/ch192a.html?qt=HIV&alt=sh through http://www.merck.com. Accessed on 10/30/08.

(2008 September, Reviewed). Human Immunodeficiency Virus – HIV. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/InfectiousDz/Viruses/HIV.html through http://www.arupconsult.com. Accessed on 10/30/08.

(2006 September 22). Revised Recommendations for HIV Testing of Adults, Adolescents, and Pregnant Women in Health-Care Settings. CDC MMWR 55(RR14);1-17 [On-line information]. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5514a1.htm through http://www.cdc.gov/mmwr. Accessed on 11/1/08.

(2008 September 26). CD4 Monitoring of HIV Patients a Cost-Saving Strategy in Poor Countries. Medscape from Reuters Health Information [On-line information]. Available online at http://www.medscape.com/viewarticle/581174 through http://www.medscape.com. Accessed on 10/26/08.

Moing, V. et. al. (2007 May 22). From HIV Medicine Long-term Evolution of CD4 Count in Patients With a Plasma HIV RNA Persistently <500 copies/mL During Treatment With Antiretroviral Drugs. Medscape from HIV Medicine [On-line information]. Available online at http://www.medscape.com/viewarticle/556494 through http://www.medscape.com. Accessed on 11/1/08.

Moore, D.M. et. al. (2006 September 13). CD4 Percentage is an Independent Predictor of Survival in Patients Starting Antiretroviral Therapy with Absolute CD4 Cell Counts Between 200 and 350 Cells/UL. Medscape from HIV Medicine [On-line information]. Available online at http://www.medscape.com/viewarticle/543496 through http://www.medscape.com. Accessed on 11/1/08.

Baker, J. et. al. (2008 July 18). CD4+ Count and Risk of Non-AIDS Diseases Following Initial Treatment for HIV Infection. Medscape from AIDS 2008;22(7): 841-848. [On-line information]. Available online at http://www.medscape.com/viewarticle/575829 through http://www.medscape.com. Accessed on 11/1/08.

Henry’s Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007. Pp 317, 600-604, 820 and 1923.

(Updated November 13, 2008) National Institute of Allergy and Infectious Diseases. Understanding How HIV Causes AIDS. Available online at http://www3.niaid.nih.gov/topics/HIVAIDS/Understanding/howhiv.htm through http://www3.niaid.nih.gov. Accessed February 2008.

LabCorp CD4:CD8 Ratio Profile. Available online through https://www.labcorp.com. Accessed February 2009.

ARUP Consult. Leukemia and Lymphoma Phenotyping. Available online at http://www.arupconsult.com/Topics/OncologicDz/Lymphomas/LeukemiaLymphomaPhenotyping.html# through http://www.arupconsult.com. Accessed March 2009.

(August 9, 2007) MayoClinic.com. DiGeorge Syndrome. Available onlien at http://www.mayoclinic.com/health/digeorge-syndrome/DS00998 through http://www.mayoclinic.com. Accessed March 2009.

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