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CD4 and CD8 Test

Last updated Sept. 22, 2018

A CD4 and CD8 Test is a blood test that assesses the numbers of CD4-containing helper T cells and CD8-containing cytotoxic T cells. It is used to diagnose HIV infection and progression of the condition. It is also used to diagnose other diseases. The results are sometimes reported as a ratio.


What are the other Names for this Test? (Equivalent Terms)

  • T4 Count Blood Test
  • T-Helper Cells Blood Test
  • T-Suppressor Cells Blood Test

What is CD4 and CD8 Test? (Background Information)

  • CD4 and CD8 are clusters of differentiation (CD) proteins on the surfaces of certain white blood cells, called lymphocytes. They interact with major-histocompatibility (MHC) proteins on the membranes of other cells
  • Lymphocytes are part of the body’s acquired or specific, immune response. It is so named, because it only develops after exposure to specific pathogens, which it can then identify and distinguish (meaning it can tell them apart). There are 2 kinds of lymphocytes:
    • T lymphocytes, or T cells
    • B lymphocytes, or B cells
  • T cells exist in several varieties, with each of them accomplishing unique, but overlapping tasks. They are distinguished by the specific CD markers that they contain
    • Helper T cells contain CD4: They recognize MHC-II of certain white blood cells. Helper T cells can then activate B cells to mount an immune response. They also produce memory cells
    • Cytotoxic T cells contain CD8: They recognize the MHC-I of all nucleus-containing cells. If they detect abnormalities, they destroy the target cell. Cytotoxic T cells constitute the body’s cell-mediated immunity, which defends from threats by virus-infected and cancerous cells
    • In addition, regulatory T cells keep the system in check. They ensure that T cells do not become overactive or mistake healthy cells for pathogens
  • B cells, when activated, turn into plasma cells. Plasma cells are antibody-producing factories. They constitute the body’s humoral immunity (“humor”, bodily fluid), which defends from threats in the serum of blood and lymph
  • HIV targets CD4-containing helper T cells. HIV resides in these cells and with time, can drastically lower their numbers. One of the criteria for diagnosis of AIDS is a CD4 count less than 200 cells/mL, when the normal value is 500-1000 cells/mL
  • A CD4 and CD8 Test is a blood test that assesses the numbers of CD4-containing helper T cells and CD8-containing cytotoxic T cells. It is used to diagnose HIV infection and progression of the condition. It is also used to diagnose other diseases. The results are sometimes reported as a ratio

What are the Clinical Indications for performing the CD4 and CD8 Test?

Following are the clinical indications for performing a CD4 and CD8 Test:

  • Monitoring the progression of a known HIV infection
  • Monitoring anti-retroviral therapy
  • Frequent and persistent infections
  • Infection by pathogens that are normally trivial, including yeasts, such as Candida albicans (oral/genital candidiasis, thrush)

How is the Specimen Collected for CD4 and CD8 Test?

Following is the specimen collection process for CD4 and CD8 Test:

Sample required: Blood

Process: Insertion of a needle into an arm vein.

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the CD4 and CD8 Test Result?

The significance of the CD4 and CD8 Blood Test is explained:

  • Decreased levels of CD4-containing helper T cells may indicate:
    • Infection with HIV
    • AIDS, if CD4 levels fall below 200 cells/mL
  • Abnormal levels of CD4-containing helper T cells may also indicate lymphoma, or other blood disorders

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: June 12, 2014
Last updated: Sept. 22, 2018