Promyelocytes are primitive cells in the bone marrow plus promyelocytes. A normal person has no more than 5% of primitive cells and promyelocytes in the bone marrow. If it exceeds 5% it is an abnormality. Between 5% and 20% is commonly seen in myelodysplastic syndrome, a malignant clonal disease of hematopoietic stem cells that is highly susceptible to transformation to leukemia. If the ratio of primitive to naive cells is greater than 20%, acute leukemia is diagnosed. Therefore, after a normal person has had a bone marrow aspiration to obtain bone marrow, the ratio of primitive to naive cells in the patient’s bone marrow can be counted by staining, which normally cannot exceed 5%. At the same time, if a patient with leukemia has undergone chemotherapy and has a new bone marrow aspiration, if the ratio of primitive to naive cells in the patient’s bone marrow is less than 5%, it means that the bone marrow is in complete remission.