A blood smear is a test in which the peripheral blood is stained and observed under a microscope to determine the number, shape and proportion of various blood cells in the peripheral blood. The blood smear test can provide a useful diagnostic basis for many diseases, especially for hematologic diseases. If an abnormally high number of leukocytes is found in the peripheral blood, along with a large number of immature primitive cells, or leukemia cells, the diagnosis of acute leukemia or chronic leukemia can be made, and further bone marrow aspiration can confirm the specific type of leukemia. By the same token, if a blood smear is taken from an earlobe or a vein and a large number of Plasmodium parasites are found, malaria can be diagnosed in this case.