This test measures the number of CD4 cells in your blood. CD4 are white blood cells, which is also known as T-cells. These cells move throughout your body and destroy all the bacteria, viruses, and other germs in your body. This test helps determine the damage that has been caused to your immune system and what might happen next if the antiretroviral treatments are not initiated. People suffering from HIV must undergo antiretroviral treatment, regardless of the CD4 count. When the patient undergoes antiretroviral treatment, the CD4 count must increase.