pernicious anemia: see anemia.

anemia, condition in which the concentration of hemoglobin in the circulating blood is below normal. Such a condition is caused by a deficient number of erythrocytes (red blood cells), an abnormally low level of hemoglobin in the individual cells, or both these conditions simultaneously. Regardless of the cause, all types of anemia cause similar signs and symptoms because of the blood's reduced capacity to carry oxygen. These symptoms include pallor of the skin and mucous membranes, weakness, dizziness, easy fatigability, and drowsiness. Severe cases show difficulty in breathing, heart abnormalities, and digestive complaints.

One of the most common anemias, iron-deficiency anemia, is caused by insufficient iron, an element essential for the formation of hemoglobin in the erythrocytes. In most adults (except pregnant women) the cause is chronic blood loss rather than insufficient iron in the diet, and, therefore, the treatment includes locating the source of abnormal bleeding in addition to the administration of iron.

Pernicious anemia causes an increased production of erythrocytes that are structurally abnormal and have attenuated life spans. This condition rarely occurs before age 35 and is inherited, being more prevalent among persons of Scandinavian, Irish, and English extraction. It is caused by the inability of the body to absorb vitamin B₁₂ (which is essential for the maturation of erythrocytes).

There are several conditions that cause the destruction of erythrocytes, thereby producing anemia. Allergic-type reactions to bacterial toxins and various chemical agents, among them sulfonamides and benzene, can cause hemolysis, which requires emergency treatment. In addition, there are unusual situations in which the body produces antibodies against its own erythrocytes; the mechanism triggering such reactions remains obscure.

There are several inherited anemias that are more common among dark-skinned people. Sickle cell disease is inherited as a recessive trait almost exclusively among blacks; the condition is characterized by a chemical abnormality of the hemoglobin molecule that causes the erythrocytes to be misshapen. In 1957 Vernon Ingram determined the amino acid sequence of hemoglobin, and found the beta-globins (which is one of the two polypeptide chain types) that are found in the tetrameric (four-chain) hemoglobin protein. In sickle cell disease a single mutation produces the amino acid valine instead of glutamic acid in one of the protein chain types that make up the hemoglobin molecule.

In thalassemia major (Cooley's anemia), which is the most serious of the hereditary anemias among people of Mediterranean, Middle Eastern, and S Chinese ancestry, the erythrocytes are abnormally shaped. Symptoms include enlarged liver and spleen and jaundice. Thalassemia major usually causes death before adulthood is reached.

Any disease or injury to the bone marrow can cause anemia, since that tissue is the site of erythrocyte synthesis. Bone marrow destruction can also be caused by irradiation, disease, or various chemical agents. In cases of renal dysfunction, the severity of the associated anemia correlates highly with the extent of the dysfunction; it is treated with genetically engineered erythropoietin.

Blood disorder (see hemoglobinopathy) seen mainly in persons of Sub-Saharan African ancestry and their descendants and in those from the Middle East, the Mediterranean area, and India. About 1 in 400 blacks worldwide has the disease, caused by inheriting two copies of a recessive gene that makes those with one copy (about 1 in 12 blacks worldwide) resistant to malaria. The gene specifies a variant hemoglobin (hemoglobin S or Hb S) that distorts red blood cells (erythrocytes) into a rigid sickle shape. The cells become clogged in capillaries, damaging or destroying various tissues. Symptoms include chronic anemia, shortness of breath, fever, and episodic “crises” (severe pain in the abdomen, bones, or muscles). Hydroxyurea treatment triggers production of fetal hemoglobin (Hb F), which does not sickle, greatly lessening severity of crises and increasing life expectancy, previously about 45 years.

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Slow-developing disease in which vitamin B₁₂ (see vitamin B complex) deficiency impairs red-blood-cell production. It can result from a diet lacking in vitamin B₁₂ or when intrinsic factor, a substance needed for intestinal absorption of B₁₂, either is not produced by stomach cells or cannot bind to the vitamin. It causes weakness, waxy pallor, shiny tongue, and stomach, intestinal, and neurological problems. Its slow development can allow anemia to become very severe by the time of diagnosis. Monthly B₁₂ injections into muscle soon reverses the anemia, but the injections must be continued for life.

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Most common type of anemia, which may develop in times of high iron loss and depletion of iron stores (e.g., rapid growth, pregnancy, menstruation) or in settings of low dietary iron intake or inefficient iron uptake (e.g., starvation, intestinal parasites, gastrectomy). Much of the world's population is iron-deficient to some degree. Symptoms include low energy level and sometimes paleness, shortness of breath, cold extremities, sore tongue, or dry skin. In advanced cases, red blood cells are small, pale, and low in hemoglobin, blood iron levels are reduced, and body iron stores are depleted. Treatment with iron usually brings quick improvement.

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or anemia of bone-marrow failure

Inadequate blood-cell formation by bone marrow. Pancytopenia is the lack of all blood-cell types (erythrocytes, leukocytes, and platelets), but any combination may be missing. Drug, chemical, or radiation exposure most often causes the disease, but about half of all cases have no known cause. It may occur at any age. Acute disease may be quickly severe, even fatal; chronic disease has symptoms including weakness, shortness of breath, headache, fever, and pounding heart. There is usually a waxy pallor. Hemorrhages occur in mucous membranes, skin, and other organs. Lack of white blood cells lowers resistance to infection and becomes the major cause of death. Very low platelet count may lead to severe bleeding. The treatment of choice is bone-marrow transplantation. Otherwise treatment involves avoiding any known toxic agent and giving fluids, glucose, and proteins (often intravenously) as well as blood components and antibiotics.

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Condition in which erythrocytes are reduced in number or volume or are deficient in hemoglobin. The patient is usually noticeably pale. Close to 100 varieties exist (including aplastic anemia, pernicious anemia, and sickle-cell anemia), distinguished by cause; erythrocyte size, shape, and hemoglobin content; and symptoms. Anemia may result from blood loss; increased destruction, reduced production, or inhibited formation of red cells; or hormone deficiency. Treatment may involve nutrition, toxin removal, drugs, surgery, or transfusion. Seealso folic-acid-deficiency anemia, iron-deficiency anemia.

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