What it measures
CD3 is a marker found on all T cells, a type of lymphocyte. The test counts how many CD3 cells are in a microlitre of blood, using a method called flow cytometry. It is usually reported with CD4 and CD8 counts as a lymphocyte subset panel.
Why people test it
- Measured when the lymphocyte count is low or an immune deficiency is suspected.
- Part of a lymphocyte subset panel with CD4 and CD8 counts.
- Monitored on some medicines, and after some transplants, that lower T cells.
Typical range
Ranges vary by lab and method, and counts are much higher in children. Results may also be given as a percentage of lymphocytes. Your report shows the lab's own range.
Finger-prick or vein?
A vein sample is needed. The cells are counted while fresh, so the sample has to reach the lab quickly, and a finger prick does not give enough blood.