Home > Encyclopedia of Nursing & Allied Health > Iron Deficiency Anemia

Definition

Anemia can be caused by iron deficiency, folate deficiency, vitamin B₁₂ deficiency, and other causes. Iron deficiency anemia is due to a shortage of iron. It is characterized by the production of red blood cells that are smaller than normal (microcytic) and appear pale or light colored (hypochromic) when viewed under a microscope. For this reason, the anemia that occurs with iron deficiency is also called hypochromic microcytic anemia.

Description

Iron deficiency anemia is the most common type of anemia throughout the world. In the United States, iron deficiency anemia occurs to a lesser extent than in developing countries because of the higher consumption of red meat and the practice of food fortification (addition of iron to foods by manufacturers). In the United States, iron deficiency anemia is caused by a variety of factors, including excessive losses of iron in menstrual fluids and excessive bleeding into the gastrointestinal tract. In developing countries located in tropical climates, the most common cause of iron deficiency anemia is infestation with hookworm.

Causes and symptoms

Infancy is a period of increased risk for iron deficiency. A human infant is born with a built-in supply of iron, which can be tapped during periods of drinking low-iron milk or formula. Both human milk and cow milk contain rather low levels of iron (0.5-1.0 mg iron/liter). However, about 50% of the iron in human milk is absorbed by an infant, while only 10% of the iron in cow milk is absorbed. During the first six months of life, growth of an infant is made possible by milk in the diet and by the infant's built-in supply. Premature infants have a lower supply of iron. For this reason, it is recommended that pre-term infants (beginning at two months of age) be given oral supplements of 7 mg iron/day, in the form of ferrous sulfate. Iron deficiency can develop when infants are fed formulas that are based on cow milk that has not been fortified. For example, unfortified cow milk is given free of charge to mothers in Chile. This practice prevents general malnutrition, but results in the development of mild iron deficiency.

The normal rate of blood loss in the feces is 0.5-1.0 ml per day. About 60% of persons with cancer of the colon and rectum experience further blood loss in the range of 10 ml/day, which can lead to iron deficiency anemia. The fecal occult blood test is widely used to screen for the presence of cancer of the colon or rectum. In the absence of testing, colorectal cancer may be first detected because of the resulting iron deficiency anemia.

Infection with hookworm can also cause iron deficiency anemia. The hookworm is a parasite that thrives in warm climates, including in the southern United States. A hookworm enters the body through the skin, very commonly through bare feet. The hookworm then migrates to the small intestines where it attaches itself to the villi (small, finger-like structures found on the walls of the intestines, which are used for the absorption of nutrients). Hookworms damage the villi, resulting in blood loss. Further, they produce anticoagulants which promote continued bleeding. Each hookworm can cause the loss of up to 0.25 ml of blood per day.

Bleeding and blood loss through the gastrointestinal tract can also be caused by hemorrhoids, anal fissures, irritable bowel syndrome, aspirin-induced bleeding, blood clotting disorders, and diverticulosis (a condition caused by an abnormal opening from the intestine). Several genetic diseases are characterized by bleeding disorders. These include hemophilia A, hemophilia B, and von Willebrand's disease. Of these, only von Willebrand's disease leads to gastrointestinal bleeding.

The symptoms of iron deficiency anemia include weakness and fatigue. These symptoms result from the lack of function of red blood cells, and the reduced ability of red blood cells to carry iron to exercising muscles. Iron deficiency can also affect other tissues, including the tongue and fingernails. Prolonged iron deficiency can result in changes of the tongue, which may become smooth, shiny, and reddened, a condition known as glossitis. Fingernails may grow abnormally and acquire a spoon-shaped appearance.

Decreased iron intake is a contributing factor in iron deficiency and the resulting iron deficiency anemia. The iron content of some common foods is:

• whole wheat bread (43 mg/kg)
• spinach (33 mg/kg)
• beef (28 mg/kg)
• raisins (20 mg/kg)
• eggs (20 mg/kg)
• lima beans (15 mg/kg)
• potatoes (14 mg/kg)
• canned tuna (13 mg/kg)
• chicken (11 mg/kg)
• peanut butter (6.0 mg/kg)
• tomatoes (3.0 mg/kg)
• cabbage (1.6 mg/kg)
• apples (1.5 mg/kg)
• corn oil (0.6 mg/kg)

It is readily apparent that apples, tomatoes, and corn oil are relatively low in iron, while whole wheat bread, spinach, and beef are relatively high in iron. The assessment of whether a food is low or high in iron can also be made by comparing the amount of that food eaten per day with the recommended dietary allowance (RDA) for iron. The RDA for iron for an adult male is 10 mg/day, while that for an adult woman is 15 mg/day. The RDA during pregnancy is 30 mg/day. The RDA for infants of 0-0.5 years of age is 6 mg/day, while that for infants of 0.5-1.0 year of age is 10 mg/day. RDA values are based on the assumption that a person eats a mixture of plant and animal foods.

The above list of iron values alone may be deceptive, because bioavailability varies. Bioavailability means the percent of iron in the food that is absorbed via the gastrointestinal tract to the bloodstream. Non-absorbed iron is lost in the feces. The bioavailability of iron in fruits, vegetables, and grains is very low, but is much higher in meats. The bioavailability of iron in plants ranges from only 1-10%, while that in meat, fish, chicken, and liver is 20-30%. The most readily absorbable source of iron is human milk, which has a 50% bioavailability.

Interactions between various foods also influence the absorption of dietary iron. Vitamin C, for example, increases the absorption of dietary iron. Thus, if rice is consumed with a vitamin C-rich food such as orange juice, then the absorption of the rice's iron is enhanced. The increased use of formulas fortified with both iron and vitamin C has led to a marked reduction in anemia in infants and young children in the United States. In contrast, if rice is consumed with tea, certain chemicals (tannins) in the tea reduce the absorption of iron. Another potent inhibitor of iron absorption is phytic acid, a chemical that occurs naturally in legumes, cereals, and nuts.

Diagnosis

Iron deficiency anemia in infants is defined as a hemoglobin level below 109 mg/ml of whole blood, and a hematocrit of under 33%. Anemia in adult males is defined as hemoglobin under 130 mg/ml and a hematocrit of under 38%. Anemia in adult females is defined as hemoglobin under 120 mg/ml and a hematocrit of under 32%. Anemia in pregnant women is defined as hemoglobin of under 110 mg/ml and a hematocrit of under 31%.

When an abnormally high presence of blood is found in feces during a fecal occult blood test, a physician needs to examine the gastrointestinal tract to determine the cause or source of bleeding. For this, a sigmoidoscope may be used. This is an instrument that consists of a flexible tube with a light at the end and allows an examiner to directly visualize and examine the interior of the large bowel or colon to a distance of 60 cm from the anus. A barium enema, with an x ray, may also be used to detect abnormalities that can cause bleeding.

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KEY TERMS

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Barium—An element used in liquid suspension with radiography (x rays) due to its high contrast with human tissue.

Diverticulitis—A disease caused by abnormal outpocketings in the walls of the intestines.

Ferrous—A form of iron that has two electrons available for chemical reactions and is readily absorbed by humans; ferrous iron is also referred to as reduced.

Gastroenterology—The study of the structures of the gastrointestinal tract, commonly including the stomach, small intestines and large intestines.

Glossitis—A condition of the tongue in which the tongue becomes red, smooth, and shiny.

Hematocrit—The proportion of whole blood in the body, by volume, that is composed of red blood cells.

Heme—A protein comprising most of the mass of red blood cells that transports oxygen and carbon dioxide.

Hemoglobin—An iron-containing protein within red blood cells. Hemoglobin accounts for about 95% of the protein in the red blood cell.

Hypochromic—Having less than normal color.

Microcytic—Cells that are smaller than normal size.

Occult—Hidden or difficult to observe.

Protoporphyrin IX—A protein. Measuring proporphyrin IX is useful to assess iron status. Hemoglobin consists of a complex of a protein plus heme. Heme consists of iron plus protoporphyrin IX. Normally during the course of red blood cell formation, protoporphyrin IX acquires iron to generate heme. Protoporphyrin IX builds up to abnormally high levels when iron is deficient.

Recommended Dietary Allowance (RDA)— Quantities of nutrients in the diet that are required to maintain human health. RDAs are established by the Food and Nutrition Board of the National Academy of Sciences and may be revised every few years.

Villi—Small, finger-like structures found on the walls of the intestines that are used for the absorption of nutrients.

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If evidence suggests that oral iron supplements are failng in treating anemia, a test for oral iron absorption is indicated. The oral iron absorption test is conducted by ingesting 64 mg iron (325 mg ferrous sulfate) in a single dose. Blood samples are then taken after two hours and four hours. The iron content of the person's serum is then measured. If iron absorption is normal, the concentration of iron should rise by an increment of about 22 micro-moles. Smaller increases in concentration mean that iron absorption is abnormal, and that therapy should involve injections or infusions of iron.

Treatment

Oral iron supplements (pills) may contain various chemical compounds containing iron, often called iron salts. Iron salts include ferrous sulfate, ferrous gluconate, or ferrous fumarate. Injections and infusions of iron can be given using a preparation called iron dextran. In patients with poor gastrointestinal absorption of iron, therapy with injection or infusion is preferable over oral supplements. Treatment of iron deficiency anemia sometimes requires more than therapy with iron. If iron deficiency is due to bleeding from hemorrhoids, surgical correction of the hemorrhoids may be essential to prevent recurrent iron deficiency anemia. If iron deficiency is caused by bleeding due to aspirin treatment, aspirin should be discontinued. If iron deficiency is due to hookworm infestations, therapy for this parasite should be given in conjunction with protection of feet by wearing shoes whenever walking in areas that are potentially infested with hookworms.

Prognosis

The prognosis for treating and curing iron deficiency anemia is excellent. One important issue, however, is failure to take iron supplements. Pregnant women may be advised to take 100-200 mg iron/day, a dose that leads to nausea, diarrhea, or abdominal pain in 10-20% of women. Such a high dosage is recommended to rapidly cure the anemia during pregnancy. Before conception, problems associated with side effects and nonadherence may be avoided by taking iron doses (100-200 mg) only once a week. This can be continued throughout a woman's fertile period. The problem of adherence is not an issue when infusions are used, although a fraction of persons treated with iron infusions experience flushing, headache, nausea, seizures, or anaphylaxis.

A number of studies have shown that iron deficiency anemia in infancy can result in reduced intelligence in early childhood. It is not clear whether iron supplementation given to children with reduced intelligence due to iron-deficiency anemia in infancy has any influence in allowing a "catch-up" in intellectual development.

Health care team roles

Screening for iron deficiency anemia is commonly conducted by nurses and physicians. However, when professionally-trained personnel are not available, other people may be given specific training to administer the screening test. Laboratory technicians process blood samples collected by screening tests. Physicians and nurses administer iron injections or intravenous infusions. Surgeons or physicians trained in gastroentnerology perform gastroscopic examinations. Radiologists interpret the results of x rays taken after infusion of a barium enema.

Prevention

In a healthy population, all mineral deficiencies can be prevented by ingesting inorganic nutrients at levels defined by the RDA. Iron deficiency anemia in infants and young children can be prevented by consuming fortified foods. Cow milk-based infant formulas are generally supplemented with iron (12 mg/L). The iron in liquid formulas is added as ferrous sulfate or ferrous gluconate. Commercial infant cereals are also fortified with iron. In addition, small particles of elemental iron may be added to the cereal. The levels used are about 0.5 gram iron/kg dry cereal, an amount about 10-fold greater than what is naturally present.

L. Fleming Fallon, Jr., MD, PhD, DrPH