Lymphocytes are part of white blood cells, and the lymphocyte ratio is the percentage of lymphocytes in the total number of white blood cells in routine blood tests, and the normal human lymphocyte ratio is between 20% and 40%. In addition, some physical and chemical factors, drug factors, as well as some pathological factors resulting in a decrease in lymphocytes or an increase in the total number of white blood cells, may cause a low lymphocyte ratio. Physicochemical factors: If the patient has been treated or injured by physical methods such as radiation, it may cause the body’s immune function to be impaired, resulting in a low lymphocyte ratio. Drug factors: Mostly seen in patients treated with glucocorticoids such as adrenocorticotropic hormone, or applying anti-lymphocyte globulin, alkylating agents, etc., which may cause low lymphocyte ratio. Pathological factors: 1. Lymphocyte reduction: Lymphocytes themselves are divided into T lymphocytes and B lymphocytes, which are important components of the human immune system. Therefore, when immunodeficiency diseases occur, such as T lymphocyte immunodeficiency disease, gammaglobulin deficiency, AIDS, etc., they can lead to a decrease in lymphocytes, so the lymphocyte ratio in the body will also appear low, and patients often have Recurrent infections, fever, etc.; 2. Increase in total white blood cells: lymphocytes, neutrophils, etc. themselves belong to one of the types of white blood cells, and when the lymphocyte ratio is low, it may also be caused by a high number of neutrophils in the whole blood. It is usually initially considered that the patient may have an acute bacterial or viral infection, such as influenza, chickenpox, whooping cough, pneumonia, rubella, urticaria, acute tonsillitis, acute appendicitis, acute cholecystitis, acute pancreatitis, etc., or has suffered severe trauma resulting from it. Certain rheumatic immune system diseases, such as rheumatoid arthritis, ankylosing spondylitis, systemic lupus erythematosus, and gout, can also cause neutrophil elevation, resulting in a low lymphocyte ratio. In addition, when patients have diseases such as acute and chronic granulocytic leukemia, the lymphocyte ratio can also be low due to malignant proliferation of neutrophils. However, the diagnosis of a specific disease needs to be made by the doctor together with other indicators in the clinical examination and the patient’s symptoms and signs, and a single abnormal value cannot make a clear diagnosis. When the cause is identified, treatment should be actively cooperated to prevent deterioration of the disease or other complications.