Lymphocyte value of 0.51 generally refers to an absolute lymphatic value of 0.51 x 10^9/L, and its normal value is: (0.8-4) x 10^9/L. Therefore, the reason for the low lymphocyte value may be certain drug treatments (e.g., the application of adrenocorticotropic hormones, alkylating agents, and anti-lymphocyte globulins) as well as radiation damage, gammaglobulin deficiency, and so forth, which should be treated according to the specific cause: discontinuation of the Drugs, avoiding exposure to radiation, medication, etc. 1. Certain medications: Low lymphocyte values caused by adrenocorticotropic hormones, alkylating agents, antilymphocyte globulin, etc. will gradually return to normal after adrenocorticotropic hormones are discontinued. Those who use alkylating agents and anti-lymphocyte globulin are related to the treatment of the primary disease, and can take whitening drugs such as Lycopodium to treat them. 2. Radiation damage: Low lymphocyte values caused by radiation will recover slowly after stopping exposure to radiation. If radiotherapy is carried out for disease reasons, the patient should be treated under the guidance of specialized doctors. 3. Gammaglobulin deficiency: it is a recessive hereditary disease, and the clinical treatment is generally based on replacement therapy, periodic injection of human serum immunoglobulin or intravenous plasma and immunoglobulin. Lymphocyte value of 0.51 × 10^9 / L may also have other causes, it is recommended to go to the hospital in a timely manner, to identify the cause of the disease and then targeted treatment should be avoided to blindly use their own drugs.