What Does CD4 Count Mean on a Blood Test?

What it means

CD4 cells are a kind of lymphocyte, a white blood cell. They act like coordinators, signalling other immune cells to respond to infections. HIV infects and destroys CD4 cells, so the number of these cells gives a picture of how strong the immune system is in someone living with HIV.

Doctors use the CD4 count to judge immune health, decide whether someone needs extra medicines to prevent certain infections, and see how the immune system is recovering on HIV treatment. The result is usually reported as cells per cubic millimetre, and some reports also give a CD4 percentage. Your report prints its own reference range. Doctors care most about the trend over months, along with the viral load.

The CD4 count is different from the viral load. Viral load measures the amount of virus, while CD4 measures the immune cells. They are often checked together because each tells part of the story.

Where you may see it

• HIV clinic results, usually next to the viral load
• First blood tests after an HIV diagnosis
• Letters deciding whether medicines to prevent certain infections are needed
• Some results for people with other immune conditions or on strong immune-lowering medicines