Merck Manual

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Iron Deficiency


Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Reviewed/Revised Dec 2021 | Modified Sep 2022
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Iron (Fe) is a component of hemoglobin, myoglobin, and many enzymes in the body. Heme iron is contained mainly in animal products. It is absorbed much better than nonheme iron (eg, in plants and grains). Nonheme iron accounts for > 85% of iron in the average diet. However, absorption of nonheme iron is increased when it is consumed with animal protein and vitamin C.

Iron deficiency is one of the most common mineral deficiencies in the world. It may result from the following:

Chronic bleeding due to colon cancer is a serious cause in middle-aged and older people.

Diagnosis of iron deficiency involves complete blood count, serum ferritin and iron levels, and possibly measurement of transferrin saturation (iron-binding capacity). In deficiency states, iron and ferritin levels tend to be low, and iron-binding capacity tends to be high.

Rarely, when the diagnosis of iron deficiency remains uncertain, examination of bone marrow for iron may be necessary.

Treatment of iron deficiency involves correcting the cause if possible (eg, treatment of a bleeding intestinal tumor). All people with moderate or severe iron deficiency and some people with mild deficiency require iron supplementation Treatment Iron deficiency is the most common cause of anemia and usually results from blood loss; malabsorption, such as with celiac disease, is a much less common cause. Symptoms are usually nonspecific... read more Treatment .

General reference

  • 1. Coates A, Mountjoy M, Burr J: Incidence of iron deficiency and iron deficient anemia in elite runners and triathletes. Clin J Sport Med 27:493–4986, 2017. doi: 10.1097/JSM.0000000000000390

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