GSTM1 and aplastic anemia: The types of anemia may be classified based on changes in RBC volume (microcytic: smaller (iron deficiency anemia, thalassemia and sideroblastic anemia); normocytic: normal (anemia of chronic disease and aplastic anemia); macrocytic: larger (megaloblastic anemia and hemolytic anemia)), Hb concentrations (hypochromic: reduced; normochromic: normal), loss of blood cells (hemolytic or hemorrhagic) and hemopoietic activity (regenerative and nonregenerative) (Tvedten, 2010).