Be on high alert when a child visits the doctor with unexplained persistent or recurrent fever, anemia, cachexia, tendency to bleed, enlarged liver, spleen and lymph nodes, pain in the bones or pressure pain in the sternum, unexplained weight loss, and gradual loss of strength. Consider whether it is leukemia. Leukemia is a malignant neoplastic disease of hematopoietic origin, characterized by uncontrolled proliferation of a series or series of blood cells in the hematopoietic tissue and infiltration of other tissues, with primitive and early infantile cells predominating in the bone marrow and peripheral blood, with common clinical manifestations such as anemia, fever and enlargement of liver, spleen and lymph nodes. Causes: 1. ionizing radiation 2. chemical factors 3. viruses 4. genetic factors Leukemia is classified into acute leukemia and chronic leukemia according to the maturation disorder of leukemia cells and the speed of disease development. Acute leukemia is divided into acute lymphoblastic leukemia and acute non-lymphoblastic leukemia. The typing of acute leukemia has evolved from a single FAB morphological typing method in the past to morphological, immunological, cytogenetic, and molecular biology (MICM) typing methods. For the diagnosis of leukemia, routine blood tests are essential and often reveal primitive or naive cells, or a significant increase or decrease in a particular type of cell. When leukemia is highly suspected, bone marrow aspiration is performed first and foremost. Bone marrow examination is the main method for diagnosing leukemia and also plays an important role in the observation of efficacy and determination of prognosis. Acute leukemia is diagnosed when the bone marrow has ≥ 20% primitive granulocytes or primitive (mono, gonadotropic) + naïve (mono, gonadotropic) cells.