What is lymphocytosis: First of all, our white blood cells include neutrophils, lymphocytes, monocytes, eosinophils and basophils, of which the number of lymphocytes only accounts for 20-30%. Mild lymphocytosis, mostly seen in some children, it is a normal phenomenon. For adults with mild lymphocytosis, if it is not accompanied by clinical symptoms, it may not be treated for the time being, while for patients with fever and infection, it may be considered a viral infection and should be treated with antiviral drugs. Some abnormal lymphocytosis. Secondly, the diagnosis of leukemia should be considered. In this case, bone marrow aspiration cytology should be done to clarify the cause of this lymphocytosis, which can be accompanied by local lymph node enlargement to exclude lymphoma, and lymph node needle aspiration cytology can be done to clarify the diagnosis.