Test guide
CD4 Lymphocyte Count
A CD4 count is a blood test that measures the number of CD4 cells in a sample of your blood. CD4 cells are a type of white blood cell that circulates throughout the body in the blood. They're also called CD4 T lymphocytes or "helper T cells." That's because they help fight infection by triggering your immune system to destroy viruses, bacteria, and other germs that may make you sick.
What it is for
If you have HIV, a CD4 count may be used to: A CD4 count may also be used to: Source: MedlinePlus, National Library of Medicine. Medical test information is public domain. Source identity and definition checked automatically on 2026-10-18. No individual clinical interpretation or human reviewer is asserted.
Limitations
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also known as
- CD4 lymphocyte count CD4+ count, T4 count, T-helper cell count, CD4 percent
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