Red cells in the marrow can be reduced in many ways: eg. by marrow damage (ie. aplasia, infiltration by other tumors, drug induced damage), decreased stimulation (ie. renal disease, certain endocrine disorders), lack of certain nutrients (ie. iron deficiency anemia , folate deficiency anemia), some hereditary disorders (ie. thalassemia, sickle cell anemia, G6PD deficiency, sideroblastic anemia), etc.