Anemia, << uh NEE mee uh, >> is a condition in which the number of healthy red blood cells falls below normal. Red blood cells pick up oxygen in the lungs and carry it to tissues throughout the body. There, the oxygen is combined with food to release energy. In an anemic person, the blood cannot provide the tissues with enough oxygen. Thus, the person feels weak or tired. Other symptoms are dizziness, headaches, pale or cool skin, rapid heartbeat, and shortness of breath.
Anemia, which is not a disease itself, is caused by a variety of diseases and disorders. The main causes are (1) insufficient production of red blood cells, (2) loss of blood, and (3) excessive destruction of red blood cells.
Insufficient production of red blood cells.
Each day, about 0.8 percent of the body’s red blood cells wear out and are destroyed. If the body fails to replace these cells at the same rate, anemia results. Red blood cells are produced in the bone marrow, a tissue in the center of certain bones. This process requires the intake of various minerals and vitamins, and the proper functioning of certain hormones in the body.
Deficiency anemias
develop if the diet lacks sufficient iron, vitamin B12, or folic acid (also called folate). These nutrients are essential for the production of red blood cells. Deficiency anemias also result if the body cannot absorb these nutrients properly. For example, pernicious anemia occurs when vitamin B12 cannot be absorbed. Physicians treat deficiency anemias by adding the missing nutrient to the diet or by administering it through injections or in tablets.
Aplastic anemias
occur if the bone marrow loses its ability to produce red blood cells. Some cases are due to diseases that affect the marrow, such as leukemia in its early stages. Other cases result from exposure to chemicals or radiation. Many cases have no apparent cause. Victims of aplastic anemia may receive a bone marrow transplant if they are young and if an appropriate donor is available. Chances of recovery are good if rejection of the transplant and infection do not occur. Other victims receive regular blood transfusions until their bone marrow begins to function again. In many cases, the marrow never regains function, and the victim requires a bone marrow transplant to survive.
Anemia of renal disease
occurs as a result of the kidney’s lost ability to produce a hormone called erythropoietin. This hormone stimulates bone marrow to make red blood cells. People whose kidneys have failed or have been removed, as well as some cancer and AIDS patients, suffer from this anemia. In 1989, the Food and Drug Administration approved Epoetin alfa, a drug that is a genetically engineered form of erythropoietin. The drug stimulates bone marrow to make red blood cells.
Loss of blood.
The body responds to excessive blood loss by retaining water to replace the fluid part of the blood. As a result, the percentage of red cells in the blood decreases and anemia develops. The blood loss may occur rapidly, as from a wound, or slowly, as from a bleeding ulcer in the stomach. Treatment involves stopping the bleeding and, if necessary, providing blood transfusions.
Excessive destruction of red blood cells.
Old red blood cells are destroyed in the liver and spleen by a process called hemolysis. If hemolysis occurs faster than the production of new red blood cells, anemia results. Such hemolytic anemia may be caused by inherited defects in the red blood cells, or it may be acquired.
Hereditary causes of hemolytic anemia include sickle cell anemia and thalassemia, disorders that affect the hemoglobin portion of red blood cells. Hemoglobin is the molecule that enables red blood cells to carry oxygen. Other hereditary defects may involve the cell membrane–the envelope that encloses a red blood cell–or the enzymes of the red blood cell. All of these hereditary disorders produce abnormal red blood cells, which are destroyed faster than normal.
Acquired hemolytic anemia can occur if the red blood cells are damaged by severe burns or freezing. It also sometimes follows infections. Normally, infections cause the body to produce antibodies, which attack the invading germs. In some cases, the body produces abnormal antibodies, called autoantibodies, which attack the person’s own red blood cells.
Treatment of hemolytic anemia varies according to the cause and severity. Treatments may include drugs, blood transfusions, removal of the spleen, or a bone marrow transplant.
