If CD4 cells are low, it is considered to be caused by malnutrition, viral infection, radiotherapy or chemotherapy, etc. It can be treated by strengthening nutrition, antiviral therapy, and supplementation of immune-boosting drugs. CD4 cells are a kind of immune cells, which play an important role in the human immune system, so testing CD4 plays an important role in determining the patient’s immune function. Normal adult CD4 cells are 500~1600 cells/ul. Low CD4 is usually seen in patients with malnutrition, prolonged late nights, viral infections and radiotherapy and chemotherapy. If it is a transient low CD4 cell, it can be recovered by strengthening nutrition and ensuring sufficient sleep. If the CD4 cells are low for a long period of time, targeted treatment is needed. Low CD4 cells are commonly associated with viral infections, with HIV being the most common, and can be gradually restored through antiviral therapy. Patients with low CD4 due to radiotherapy, chemotherapy or the use of immunosuppressive drugs need nutritional supplements and immune-boosting drugs to restore CD4. If CD4 is found to be low, it is best to go to the hospital to check the cause of the disease and follow the doctor’s instructions for treatment.