Low lymphocyte ratio is usually reflected in the routine blood test. It may be due to a slight decrease in lymphocytes as a result of blood dilution caused by drinking a lot of water recently or other reasons. In addition, the above situation can also occur during pregnancy. As the gestational weeks increase, the fetus is growing and developing, and the neutrophils increase resulting in a lower lymphocyte ratio. Some external factors and diseases can also reduce the lymphocyte ratio in clinical practice. External factors: 1. Drugs: Long-term use of hormonal drugs such as adrenocorticotropic hormones, or chemotherapy drugs such as alkylating agents, as well as anti-lymphoglobulin and other drug therapy can reduce lymphocytes. Lymphocyte death will occur, lymphocyte reduction, conditions allow, need to avoid exposure to radiation. Second, disease factors: 1, infectious diseases: when patients have cellulitis, abdominal infections and inflammatory diseases due to infection, etc., will lead to a decrease in the lymphocyte ratio. Especially when there is acute bacterial infection in the organism and the pathogen is pyogenic cocci, such as Staphylococcus aureus and Streptococcus hemolyticus, it will lead to a decrease in lymphocyte ratio, and antibacterial treatment can be given at this time; the presence of viral infections, such as HIV virus and new coronavirus, will also lead to a decrease in lymphocyte ratio, and the application of antiviral drugs, such as acyclovir and ribavirin, will be treated in daily life If the patient has gammaglobulin deficiency, immune hemolytic anemia and other diseases, the lymphocytes will be significantly reduced. 3, blood system diseases: If there is a problem with bone marrow hematopoiesis, it will lead to a decrease in the total number of lymphocytes, which can lead to a low lymphocyte ratio. In this case, bone marrow aspiration is needed to further clarify the diagnosis, and if the diagnosis is confirmed, radiation and chemotherapy may be required.