A CD4 lymphocyte count is a blood test that counts CD4 cells, a type of immune cell. It is different from a CD4 percentage, a CD4/CD8 ratio and an HIV viral load.
The result estimates how many CD4 cells are present in a blood sample. CD4 cells are part of the immune system. In people living with HIV, the count helps assess immune function and the risk of some infections.
The result can change over time, and a single value may not show the full picture. Doctors consider the trend, the laboratory's reference information, medicines, other health conditions and the rest of the clinical assessment.
The CD4 count is the absolute number of CD4 cells in a given volume of blood. CD4 percentage is the proportion of lymphocytes that are CD4 cells. The CD4/CD8 ratio compares the CD4 and CD8 cell counts. These are separate results, so the label and unit on the report matter.
Viral load measures the amount of HIV in the blood. It answers a different question from the CD4 count, which describes part of the immune system. In HIV care, the two results are considered together.
No. Other illnesses and some medicines can also lower a CD4 count. HIV is diagnosed with HIV testing, not from a low CD4 count alone.
If the result is unexpected, its meaning depends on why the test was ordered and how it compares with earlier results. The count alone does not identify the cause.

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