There are various possible diseases causing CD4 decline, such as AIDS, nutritional diseases, malignant tumor treatment period and other diseases, which need to be clearly diagnosed by different means of examination. 1. AIDS: HIV mainly targets CD4+ T lymphocytes in the human body. After infection with HIV, HIV will attack CD4+ T cells, causing CD4 decline. Once found that the body CD4 decline, need to consider the possibility of HIV infection, as soon as possible to go to the local CDC for HIV antigen, antibody testing, in order to clarify the diagnosis. 2. Nutritional diseases: when the body is in severe malnutrition or immunocompromise, it may also lead to CD4T lymphocyte decline. 3. Malignant tumor treatment period: when patients with malignant tumors are undergoing chemotherapy or radiotherapy, it will affect the body’s hematopoietic system and also have a killing effect on lymphocytes, which may also lead to a downward trend in CD4. 4. Other diseases: when there is cytomegalovirus infection, hepatitis, measles, can also cause CD4 decline. In addition, the decline of bone marrow hematopoiesis in patients with aplastic anemia and leukemia may also cause the decline of CD4T lymphocytes. When CD4 decline occurs, you can actively go to the clinic to clarify the cause of the disease and then carry out targeted treatment.