A CD4 count is a test that measures the number of CD4 cells in your blood. CD4 cells, also

known as T cells, are white blood cells that fight infection and play an important role in your

immune system. A CD4 count is used to check the health of the immune system in people

infected with HIV (human immunodeficiency virus).A normal CD4 count is from 500 to

1,400 cells per cubic millimeter of blood. CD4 counts decrease over time in persons who

are not receiving ART. At levels below 200 cells per cubic millimeter, patients become

susceptible to a wide variety of OIs, many of which can be fatal.