High lymphocytes means that the absolute value and proportion of lymphocytes exceeds the normal range. The proportion of lymphocytes in normal people is 20%-40% and the absolute value is 400-2000/mL, exceeding the normal range is high lymphocytes. The most common clinical causes of high lymphocytes: i. Various viral infectious diseases, such as acute colds, rubella, and viral infections, will show an increase in the number and proportion of lymphocytes. Second, patients with infectious mononucleosis as well as patients with infectious lymphocytosis will show a significant increase in the number and proportion of lymphocytes. Third, blood system diseases, most commonly acute lymphocytic leukemia and chronic lymphocytic leukemia, cause a serious increase in the number and proportion of lymphocytes in the peripheral blood due to the proliferation of leukemia cells in the bone marrow and their release into the peripheral blood, and at the same time, these patients are often accompanied by a series of symptoms such as anemia and thrombocytopenia. Therefore, if there is an increase in the number of lymphocytes in the peripheral blood, along with symptoms such as anemia and bleeding, one should be alert to the possibility of acute lymphoblastic leukemia.