ANEMIA

also spelled Anaemia, condition in which the red cells of the blood (erythrocytes) are reduced in number or volume or are deficient in hemoglobin, their oxygen-carrying pigment. There are close to 100 different varieties of anemia, distinguished by the cause, the size and hemoglobin content of the abnormal cells, and the symptoms. Causally, anemia may result from any of the following: (1) Chronic or acute blood loss. (2) Increased destruction of the red cells (hemolysis). This may be caused by hereditary cell defects, as in sickle-cell anemia, hereditary spherocytosis, or glucose-6-phosphate dehydrogenase deficiency. It may be caused by exposure to hemolytic chemicals (substances causing the release of hemoglobin from the red cells) such as sulfanilamide, primaquine, or naphthalene (mothballs). Or it may be caused by development of antibodies against the red blood cells, as in erythroblastosis fetalis. (3) Reduced production of red cells. This may be caused by disorders of the bone marrow, as in leukemia and aplastic anemia. It may be caused by deficiency of one or more of the nutrients, notably vitamin B12, folic acid, and iron, that are necessary for the synthesis of red blood cells. It may be caused by deficiency of certain hormones. Or it may be caused by inhibition of the red-cell-forming processes by certain drugs or by toxins produced by disease, particularly chronic infection, widespread cancer, and kidney failure. Structurally, the anemias generally fall into the following types: (1) macrocytic anemia, characterized by larger-than-normal red cells (e.g., pernicious anemia); (2) normocytic anemia, characterized by a decrease in the number of red cells, which are otherwise relatively normal (e.g., anemia caused by sudden blood loss, as in bleeding peptic ulcer, most cases of hemophilia, and purpura); (3) simple microcytic anemia, characterized by smaller-than-normal red cells (encountered in cases of chronic inflammatory conditions and in renal disease); and (4) microcytic hypochromic anemia, characterized by a reduction in red-cell size and hemoglobin concentration (frequently associated with iron-deficiency anemia but also seen in thalassemia). The most noticeable outward symptom of anemia is usually pallor of the skin, mucous membranes, and nail beds. Symptoms of tissue oxygen deficiency include pulsating noises in the ear, dizziness, fainting, and shortness of breath. Compensatory action of the heart may lead to its enlargement and to a rapid pulse rate. The treatment of anemia varies greatly, depending on the diagnosis. It includes supplying the missing nutrients in the deficiency anemias, detecting and removing toxic factors, improving the underlying disorder with drugs and other forms of therapy, decreasing the extent of blood destruction by methods that include surgery (e.g., splenectomy), or restoring blood volume with transfusion. See also aplastic anemia; equine infectious anemia; pernicious anemia; sickle-cell anemia.