sickle-cell anemia

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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