Aplastic anemia, also spelled aplastic anaemia, is a rare disease in which the bone marrow, and the hematopoietic stem cells that reside there, are damaged. This causes a deficiency of all three blood cell types (pancytopenia): red blood cells (anemia), white blood cells (leukopenia), and platelets (thrombocytopenia). Aplastic refers to inability of the stem cells to generate mature blood cells.