A single decrease in white blood cells cannot confirm a diagnosis of leukemia, so there is no such thing as how many low white blood cells are leukemia. Leukemia is a malignant disease with abnormal hematopoietic stem cells, resulting in a large number of white blood cells accumulating in the bone marrow due to impaired differentiation and abnormal proliferation of white blood cells. The exact number of white blood cells is related to the type of leukemia and the severity of the disease, and most are above the normal range or can be below or equal to normal. Normally, only mature leukocytes enter the peripheral blood. However, in patients with leukemia, immature leukemia cells in the bone marrow can also enter the peripheral blood, and this is when routine peripheral blood tests reveal elevated white blood cell values. When primitive cells from the bone marrow are not released into the peripheral blood and because normal hematopoiesis is suppressed, a decrease in leukocytes usually occurs at this time. In addition to changes in white blood cell values, the presence of primitive and immature cells in the peripheral blood is more relevant to the diagnosis of leukemia. If abnormal white blood cells are present, further investigations should be conducted as prescribed by the doctor to clarify the cause of the abnormal white blood cells and to actively cooperate with the treatment.