T-4 count: A test that counts the number of T- 4 cells in the blood, usually to assess the immune status of a patient with the HIV virus (AIDS). It's important to note that there are also T-4 cells in the lymphatic system, and they may be more severely affected there than in the bloodstream. Of the various ways to read this test, the best indicator of health may be the absolute T-4 count. Also known as T-helper count and the CD-4 cell count.
See also: T cells.