The CD4 test is performed after HIV infection to determine the immune function of the patient and what state he or she is in. As the virus continues to replicate and attack the immune system, the patient’s CD4 cell count will drop, and when it drops to a certain level, various infections will easily occur, and most AIDS patients will die from secondary opportunistic infections. The majority of AIDS patients die from secondary opportunistic infections, so it is important to check CD4 lymphocyte count after HIV infection because it is a very important immune indicator, especially for AIDS patients. In fact, as long as AIDS patients adhere to antiviral treatment and suppress the replication of the virus in their bodies, their immune function can gradually recover and CD4 cells can slowly rise and eventually reach a level close to that of a normal person.