What it measures
The number of CD4 helper T cells divided by the number of CD8 cytotoxic T cells. Both are white blood cells of the immune system, counted in a whole-blood sample. The ratio is worked out from the two counts.
Why people test it
- Monitoring the immune system in people living with HIV, alongside 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
Ranges vary by lab, method, age and sex, and your report shows the lab's own range. The ratio is read together with the CD4 and CD8 counts it comes from.
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.