Differential blood count is performed to determine the relative proportion of blood cell types within the bloodstream. In particular, the percentage of immature leukemic “blast” cells is noted. People with acute leukemia (either acute lymphocytic leukemia [ALL] or acute myelogenous leukemia [AML]) often have too many leukocytes (white blood cells), too few erythrocytes (red blood cells) and/or too few platelets. Often many of the leukocytes in these individuals are immature “blast” cells.