CD4 Count
- Also Known As:
- T4 Count
- T-helper Cells
- CD4 Percent
- Formal Name:
- CD4 Lymphocyte Count

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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 and to monitor the effectiveness of treatment; occasionally, it may be used with other conditions (see Common Questions below).
When To Get Tested?
When you are first diagnosed with HIV infection to get a baseline assessment of your immune system; about every 3 to 6 months after starting antiretroviral therapy (ART) to check whether you are responding to treatment; if you have responded well to treatment, you may then be tested every 6 to 12 months.
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
What is being tested?
CD4 cells are white blood cells called T lymphocytes or T cells that fight infection and play an important role in immune system function. CD4 tests measure the number of these cells in the blood and, in conjunction with an HIV viral load test, help assess disease status in a person who has been diagnosed with human immunodeficiency virus (HIV) infection.
CD4 cells are made in the thymus gland and they circulate throughout the body in the blood and lymphatic system. They are so called because they have markers on their surfaces called clusters of differentiation (CD). The CD number identifies the specific type of cell.
CD4 cells are sometimes called T-helper cells. They help to identify, attack, and destroy specific bacteria, fungi, and viruses that cause infections. CD4 cells are also 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.
If HIV goes untreated, the virus gets into the cells and replicates, the viral load increases, and the number of CD4 cells in the blood gradually declines. The CD4 count decreases as the disease progresses. If left untreated, this process may continue for several years until the number of CD4 cells drops to a low enough level that symptoms associated with AIDS begin to appear.
Treatment for HIV infection, called antiretroviral treatment (ART or ARV) or sometimes highly active antiretroviral therapy (HAART), typically involves taking a combination of drugs. This treatment reduces the amount of HIV (viral load) present in the body and reduces the risk of disease progression. When this occurs, the CD4 count will increase and/or stabilize.
CD4 counts can be variable, even in healthy individuals. To provide a clearer picture of the condition of the immune system, test results may also be reported as a CD4 percentage, which is the ratio of CD4 cells to total lymphocytes.
CD4 tests may be used occasionally in other conditions, such as lymphomas and organ transplantation (see Common Questions below).
Common Questions
View Sources
Sources Used in Current Review
2019 Review completed by Jenna Rychert, PhD, D(ABMM), Medical Director, ARUP Laboratory.
IDSA Guideline: Primary Care Guidelines for the Management of Persons Infected With HIV: 2013 Update by the HIV Medicine Association of the Infectious Diseases Society of America. Available online at https://www.idsociety.org/globalassets/idsa/practice-guidelines/primary-care-guidelines-for-the-management-of-persons-infected-with-hiv-2013-update-by-the-hiv-medicine-association-of-the-infectious-diseases-society-of-america.pdf. Accessed April 10, 2019.
NEW YORK STATE DEPARTMENT OF HEALTH AIDS INSTITUTE Guideline: Virologic and Immunologic Monitoring. June 2016. Available online at https://www.hivguidelines.org/antiretroviral-therapy/cd4-and-viral-load-monitoring/#tab_0 Accessed. April 10, 2019.
NIH AIDSinfo Guideline: Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. March 2019. Available online at https://aidsinfo.nih.gov/contentfiles/lvguidelines/adult_oi.pdf. Accessed April 10, 2019.
NIH AIDSinfo Guideline: Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents Living with HIV. October 2018. Available online at https://aidsinfo.nih.gov/contentfiles/lvguidelines/adultandadolescentgl.pdf. Accessed April 10, 2019.
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