Anemia is a below-normal concentration of hemoglobin in the blood, caused by a decreased number of red blood cells. Common symptoms include fatigue, rapid heartbeat, shortness of breath, and pale skin. Treatments for anemia include supplements like iron, cyanocobalamin (vitamin B12), folic acid, and medications like erythropoietin and darbepoetin. Iron deficiency is a common cause of anemia and can cause complications if left untreated. Sickle cell anemia can be treated with hydroxyurea or pentoxifylline to reduce painful crises.