GSTM1 and anemia (phenotype): The types of anemia can be classified based on changes in red blood cell (RBC) volume (microcytic: smaller; normocytic: normal; macrocytic: larger), Hb concentrations (hypochromic: reduced; normochromic: normal), loss of blood cells (hemolytic or hemorrhagic) and hemopoietic activity (regenerative and non-regenerative) (Tvedten, 2010).