This condition is marked by the presence of an abnormally low number of red blood cells or hemoglobin molecules, which are the iron-containing compound in red blood cells that transport oxygen. There are many different types of anemia, each one with its own cause. As a group, anemias are the most common disease affecting the blood.
In a healthy person, red blood cells are produced in the bone marrow and have a life span of approximately 120 days, at which point new red blood cells replace them. In healthy individuals, the formation of new red blood cells balance the destruction of old cells, and the amount of hemoglobin remains steady within the normal range. Anemia can result if red blood cells are destroyed prematurely, if the bone marrow loses the ability to make a sufficient number of new red blood cells, or if a person experiences blood loss. The net result is a deficiency in red blood cells or hemoglobin. This loss in the body's ability to transport oxygen produces the symptoms of anemia.
Most anemias start with mild symptoms that may hardly be noticed. Symptoms worsen as the disease progresses. A person with anemia may feel fatigue and appear paler than usual. The pallor is more apparent in the nail beds of the fingers and toes, the inside of the lips and eyelids, as well as the palms, where the creases may become as pale as the skin surrounding them. The heart rate often increases as the heart works harder to pump blood throughout the body in an effort to compensate for the oxygen deficit. Shortness of breath when exercising may also occur.
The most common cause of anemia is iron deficiency. Since iron is an essential component of hemoglobin, an iron deficiency leaves the body unable to produce enough hemoglobin to meet its needs. The usual causes of iron-deficiency anemia are inadequate diet, poor absorption of iron from food, and blood loss. In the United States, blood loss is the most common cause of iron deficiency in adults, which may be caused by conditions such as ulcers, colon polyps, colon cancer, or by the use of nonsteriodial anti-inflammatory drugs (NSAIDs).
Insufficient Vitamin B12 causes pernicious anemia . Insufficient folic acid produces a folic acid deficiency anemia. Since Vitamin B12 and folate are important building blocks for red blood cells, insufficient Vitamin B12, or folic acid, results in an inability of the bone marrow to produce enough new red blood cells to replace old ones.
Hemolytic anemias involve disease processes in which red blood cells break down faster than bone marrow can produce them. The most common cause of hemolytic anemia is an acquired to one's own red blood cells. Antibodies attack the cells as if they are foreign to the body and subsequently destroy them. Hemolytic anemia can also develop as a result of taking certain medications or from an inherited defect in enzymes, such as glucose-6-phosphate dehydrogenase (G6PD).
In aplastic anemias, the bone marrow fails to properly develop all types of blood cells, including red blood cells.
Certain inherited anemias involve genetic abnormalities that cause the body to manufacture defective hemoglobin. Examples include sickle cell anemia and the thalassemias.
Many infections and chronic diseases occur in conjunction with anemia. Anemias that occur along with a chronic disease are relatively common, and probably result from a combination of factors, including a decrease in the ability of the bone marrow to produce red blood cells, a shortened red blood cell life span, and impaired iron utilization. Examples of causative disease include endocarditis (inflammation of the lining of the heart that usually involves the heart valves), osteomyelitis (inflammation of the bones), juvenile rheumatoid arthritis, rheumatic fever, Crohn's Disease and ulcerative colitis.
Source: AMA Complete Encyclopedia, Copyright 2003, American Medical Association
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