Diseases that cause low lymphocyte percentage include infections, immune disorders, tuberculosis, physical and chemical factors, and hereditary diseases. Lymphocyte is a kind of white blood cell classification, normal adult lymphocyte accounts for 20%~40%, below the lower limit of normal value is low lymphocyte percentage. 1. Infections: e.g. human immunodeficiency virus infection, new coronavirus, bacterial infection, etc. 2. Immune diseases: such as lupus erythematosus, rheumatic or rheumatoid diseases, autoimmune hemolytic anemia. 3. Tuberculosis: early lymphopenia in tuberculosis. 4. Physical and chemical factors: such as long-term application of glucocorticoids, alkylating agents, anti-lymphocyte globulin therapy, radiation damage, etc. 5. Hereditary diseases: such as gammaglobulin deficiency, etc. Patients with low lymphocyte percentage should consult a doctor in time, and be diagnosed by a professional physician with medical history, symptoms, laboratory tests and other relevant auxiliary tests, and should follow the doctor’s instructions for treatment at the same time.