The CD4 count test is also known as the CD4 lymphocyte count test. This test helps to measure the strength of the immune system in case one has diagnosed with HIV infection. It also helps to monitor the effectiveness of undergoing treatment for HIV. The CD4 count test is done: • In case one is diagnosed with HIV infection • To monitor undergoing antiretroviral therapy • After every 6 to 12 months post-antiretroviral therapy