Blood Disorders Affecting Red Blood Cells. Blood disorders that affect red blood cells include: Anemia: People with anemia have a low number of red blood cells. Mild anemia often causes no symptoms.More severe anemia can cause fatigue, pale skin, and shortness of breath with exertion. Iron-deficiency anemia: Iron is necessary for the body to make red blood cells. Low iron intake and loss of blood due to menstruation are the most common causes of iron-deficiency anemia.lood Disorders Affecting Red Blood Cells. Blood disorders that affect red blood cells include: Anemia: People with anemia have a low number of red blood cells. Mild anemia often causes no symptoms.