Iron Deficiency : Part 8

by CDC

(Page 8 of 11)

A transferrin saturation of less than 16% among adults is often used to confirm iron deficiency. Among nonpregnant women of childbearing age, the sensitivity of low transferrin saturation (less than 16%) for iron deficiency as defined by no stainable bone marrow iron is 20%, and the specificity is 93%.

The factors that affect serum iron concentration and TIBC, such as iron status, diurnal variation, and day-to-day variation within persons, can affect the measured transferrin saturation as well. The diurnal varation is larger for transferrin saturation than it is for Hb concentration or Hct. Transferrin saturation is an indicator of iron-deficient erythropoiesis rather than iron depletion; hence, it is less sensitive to changes in iron stores than is serum ferritin concentration. The cost of assessing transferrin saturation and the unavailability of simple, clinic-based methods for measuring transferrin saturation hinder the use of this test in screening for iron deficiency.

Justification for Recommendations

These recommendations are intended to guide primary health-care providers in preventing and controlling iron deficiency in infants, preschool children, and women of childbearing age (especially pregnant women). Both primary prevention through appropriate dietary intake and secondary prevention through detecting and treating iron-deficiency anemia are discussed.

Primary Prevention

Primary prevention of iron deficiency means ensuring an adequate intake of iron. A reliable source of dietary iron is essential for every infant and child's growth and development, because a rapid rate of growth and low dietary iron may predispose an infant to exhaustion of iron stores by ages 4-6 months. Primary prevention of iron deficiency is most important for children aged less than 2 years, because among all age groups they are at the greatest risk for iron deficiency caused by inadequate intake of iron. The adequacy of the iron content of an infant's diet is a major determinant of the iron status of the infant as a young child, as indicated by declines in the prevalence of iron-deficiency anemia that correspond with improvements in infant feeding practices. In infants and young children, iron deficiency may result in developmental and behavioral disturbances.

The evidence for the effectiveness of primary prevention among pregnant women is less clear. Although iron-deficiency anemia during pregnancy is associated with preterm delivery and delivering a low-birthweight baby, well designed, randomized control trials are needed to evaluate the effectiveness of universal iron supplementation on mitigating adverse birth outcomes. Some studies have indicated that adequate iron supplementation during pregnancy reduces the prevalence of iron-deficiency anemia, but over the last few decades, the recommendation by the Council on Foods and Nutrition and other groups to supplement iron intake during pregnancy has not resulted in a reduced prevalence of anemia among low-income, pregnant women. Evidence on iron supplement use is limited, however, so it is not known how well the recommendation has been followed. Conclusive evidence of the benefits of universal iron supplementation for all women is lacking, but CDC advocates universal iron supplementation for pregnant women because a large proportion of women have difficulty maintaining iron stores during pregnancy and are at risk for anemia, iron-deficiency anemia during pregnancy is associated with adverse outcomes, and supplementation during pregnancy is not associated with important health risks.

Potential Adverse Effects of Increasing Dietary Iron Intake

Approximately 3.3 million women of childbearing age and 240,000 children aged 1-2 years have iron-deficiency anemia; conversely, up to one million persons in the United States may be affected by iron overload due to hemochromatosis. Hemochromatosis is a genetic condition characterized by excessive iron absorption, excess tissue iron stores, and potential tissue injury. If undetected and untreated, iron overload may eventually result in the onset of morbidity (e.g., cirrhosis, hepatomas, diabetes, cardiomyopathy, arthritis or athropathy, or hypopituitarism with hypogonadism, usually between ages 40 and 60 years. Clinical expression of iron overload depends on the severity of the metabolic defect, the presence of sufficient quantities of absorbable iron in the diet, and physiological blood loss from the body (e.g., menstruation). Transferrin saturation is the recommended screening test for hemochromatosis; a repeated high value indicates hemochromatosis. Preventing or treating the clinical signs of hemochromatosis involves repeated phlebotomy to remove excess iron from the body.

Although increases in iron intake would seem contraindicated in persons with hemochromatosis, there is no evidence that iron fortification of foods or the use of a recommended iron supplementation regimen during pregnancy is associated with increased risk for clinical disease due to hemochromatosis. Even when their dietary intake of iron is approximately average, persons with iron overload due to hemochromatosis will require phlebotomy to reduce their body's iron stores.

Secondary Prevention

Secondary prevention involves screening for, diagnosing, and treating iron deficiency. Screening tests can be for anemia or for earlier indicators of iron deficiency (e.g., erythrocyte protoporphyrin concentration or serum ferritin concentration). The cost, feasibility, and variability of measurements other than Hb concentration and Hct currently preclude their use for screening. The decision to screen an entire population or to screen only persons at known risk for iron deficiency should be based on the prevalence of iron deficiency in that population.

About the Author

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The Centers for Disease Control and Prevention (CDC) is one of the 13 major operating components of the Department of Health and Human Services (HHS), which is the principal agency in the United States government for protecting the health and safety of all Americans and for providing essential human services, especially for those people who are least able to help themselves.