What it measures
The number of CD8 T cells in a microlitre of blood. CD8 T cells, also called cytotoxic T cells, are white blood cells that destroy cells infected by viruses. They are counted in a whole-blood sample.
Why people test it
- Monitoring the immune system in people living with HIV, usually with the CD4 count.
- Checking immune cells after an organ transplant or while on a medicine that lowers immunity.
- Investigating frequent or unusual infections, as part of a wider look at white blood cells.
Typical range
University Hospitals Sussex's laboratory gives an adult range of 200 to 900 cells/µL. Ranges vary by lab, method, age and sex, and your report shows the lab's own range. Source: University Hospitals Sussex NHS Foundation Trust, Pathology: CD4/8 counts (T lymphocyte subsets).
Finger-prick or vein?
A vein sample is advised, and providers offer this test only from a vein, at a clinic or with a visiting nurse. The cells need to reach the lab intact within about two days, and finger-prick samples can clot, which upsets cell counts.
A T-cell count is not a test for HIV. HIV is diagnosed with an antigen and antibody test.