Blood smears are fine and cannot rule out leukemia. Bone marrow aspiration and biopsy are needed to confirm the diagnosis of leukemia, and blood smear cannot completely replace bone marrow aspiration and biopsy. If there are unexplained fever, enlarged liver, spleen and lymph nodes, a blood smear can be done to see the classification of peripheral blood cells and to observe whether there are naïve cells under the microscope. Because in the early stage of leukemia, the blood routine may be completely normal, and the detection rate of naïve cells will decrease when the leukocytes decrease (or even in the normal range), and at this time, it is necessary to do further bone marrow to clarify the diagnosis. In some cases, it is not possible to determine whether a patient has leukemia on the basis of routine blood tests and blood smears alone. In clinical practice, it is necessary to combine the symptoms, past medical history, blood test + blood smear and bone marrow examination to improve the accuracy of early diagnosis of leukemia and reduce misdiagnosis and omission. Diagnosis should be made under the guidance of a physician.