(See also Overview of Anemia.)
Iron deficiency anemia usually develops slowly because it may take several months for the body’s iron reserves to be used up. As the iron reserves are decreasing, the bone marrow gradually produces fewer red blood cells. When the reserves are depleted, the red blood cells are not only fewer in number but also abnormally small.
Iron deficiency is one of the most common causes of anemia, and blood loss is the most common cause of iron deficiency in adults. In men and postmenopausal women, iron deficiency usually indicates bleeding in the digestive tract. In premenopausal women, menstrual bleeding is the most common cause of iron deficiency. Iron deficiency may also result from too little iron in the diet during times of increased iron requirements such as in infants, young children, adolescent girls, and pregnant women. Decreased iron absorption in the digestive tract, called malabsorption, can result from a variety of disorders of which celiac disease is the most common.
Symptoms of iron deficiency anemia tend to develop gradually and are similar to symptoms produced by other types of anemia, such as fatigue, weakness, and paleness. Many people with severe iron deficiency anemia have pica. People with pica have a craving to ingest something, most commonly ice but sometimes a substance that is not food, such as dirt, clay, or chalk.
Once blood tests show a person has anemia, tests for iron deficiency are often done. With iron deficiency, the red blood cells tend to be small and pale. Blood levels of iron and transferrin (the protein that carries iron when it is not inside red blood cells) are measured and compared.
The most accurate test for iron deficiency is a measurement of the blood level of ferritin (a protein that stores iron). A low level of ferritin indicates iron deficiency. However, sometimes ferritin levels are misleading because they can be falsely elevated (and thus appear normal) due to liver damage, inflammation, infection, or cancer.
Because excessive bleeding is the most common cause of iron deficiency, the first step is to locate its source and stop the bleeding.
Normal dietary iron intake usually cannot compensate for iron loss due to chronic bleeding, and the body has a very small iron reserve. Consequently, lost iron must be replaced by taking iron supplements.
Correcting iron deficiency anemia with iron supplements usually takes 3 to 6 weeks, even after the bleeding has stopped. Iron supplements are usually taken by mouth. Iron supplements make the stool look dark or black and often cause constipation. An iron supplement is absorbed best when taken 30 minutes before breakfast with a source of vitamin C (either orange juice or a vitamin C supplement). Iron supplements are typically continued for 6 months after the blood counts return to normal to fully replenish the body’s reserves. Sometimes, iron is given by vein (intravenously) when large amounts of iron are needed or when the person cannot tolerate taking iron by mouth.
Blood tests are done periodically to ensure that the iron supply is sufficient.
Treating the iron deficiency treats pica.