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Hemoglobin Not an Accurate Test for Iron Deficiency
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Am Fam Physician. 2005 Nov 1;72(9):1842.
Hemoglobin is commonly measured in children between one and three years of age to detect iron deficiency. White reviewed data from the National Health and Nutrition Examination Survey (NHANES) III to determine if the presence of anemia is a positive predictor for iron deficiency and if the absence of anemia rules out the diagnosis of anemia. White also studied the usefulness of testing according to demographic data.
The study diagnosed anemia from information provided in NHANES III, a stratified population-based database of children 12 to 35 months of age. Iron deficiency was diagnosed if at least two of the following three signs were present: ferritin greater than 10 ng per mL (10 mcg per L); transferrin saturation less than 10 percent; and free erythrocyte protoporphyrin greater than 79.78 mcg per dL (1.42 μmol per L) red blood cells. Anemia was diagnosed if hemoglobin concentration was less than 11 g per dL (110 g per L). The diagnosis of iron deficiency anemia was given if anemia and iron deficiency were present.
Of the study particpants, there were 1,149 children without iron deficiency, 140 with iron deficiency, 48 with iron deficiency anemia, and 106 had anemia without iron deficiency. The 140 children with iron deficiency were more likely to have lower hemoglobin concentrations, be from households with incomes below the poverty level, and have parents who described themselves as Mexican American.
In this study, the positive predictive values and sensitivities varied with cutoffs for hemoglobin. With lower cutoffs, the positive predictive value modestly increased, whereas sensitivity decreased. Thus, even at a hemoglobin concentration cutoff of 10.7 g per dL (107 g per L), the positive predictive value was less than 30 percent. The prevalence of anemia from all causes in children one to five years of age was 9.6 percent. Only one third of children with anemia in this study were iron-deficient, and only one third of those with iron deficiency had a hemoglobin concentration below the 11 g per dL cutoff; therefore, the authors conclude that hemoglobin concentration is not a good test to diagnose iron-deficient anemia. Although the demographic subgroups examined in this study were small for statistical analysis, there appears to be no demographic group where greater usefulness of hemoglobin testing is likely.
The authors state that hemoglobin should not be considered an accurate proxy for iron deficiency, while acknowledging that iron deficiency remains a serious problem among children in the United States. They recommend primary prevention in the form of routine iron supplementation.
White KC. Anemia is a poor predictor of iron deficiency among toddlers in the United States: for heme the bell tolls. Pediatrics. February 2005;115:315–20.
editor’s note: The last U.S. Preventive Services Task Force (USPSTF)1 recommendation on iron deficiency anemia screening was published in 1996 and is under review. The current task force recommendation is to screen only high-risk infants (those in lower socioeconomic groups or in developing countries). The reasoning is that the prevalence of iron deficiency anemia is low, and in low-risk groups is unlikely to be harmful; whereas in high-risk groups, iron deficiency anemia interferes with growth and thus warrants detection. However, this does not solve the problem of poor sensitivity and specificity found in this study. If the health risks from iron deficiency anemia are indeed highest in high-risk groups, it makes sense to modify the author’s recommendation to treat all infants with supplementary iron and target the high-risk group for prophylactic treatment until the USPSTF’s updated review provides more information about screening.—c.w.
1. U.S. Preventive Services Task Force. Screening for iron deficiency anemia. 1996. Accessed online September 15, 2005, at: http://www.ahrq.gov/clinic/uspstf/uspsiron.htm.
Copyright © 2005 by the American Academy of Family Physicians.
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