Anemia Is a Poor Predictor of Iron Deficiency Among Toddlers in the United States: For Heme the Bell Tolls

Abstract

Context. Many toddlers in the United States have their hemoglobin (Hb) measured periodically. Is this worthwhile? Objective. To determine if the presence of anemia correctly diagnoses iron deficiency (ID) and if the absence of anemia correctly rules out ID in young children. Methodology. An analysis of data from the US National Health and Nutrition Examination Survey III (1988–1994) was performed. Subjects were children 12 to 35 months old for whom complete blood counts and cardinal measures of iron nutrition (ferritin, transferrin saturation, and free erythrocyte protoporphyrin) were reported. Results. In the US National Health and Nutrition Examination Survey III, the prevalence of ID ranged from 6% to 18% in various subpopulations of toddlers. In the general population, the positive predictive value of Hb concentration ([Hb]) <110 g/L for ID was 29% (95% confidence interval [CI]: 20–38%), and the sensitivity was 30% (95% CI: 20–40%). Changing the diagnostic cutoff point to [Hb] <107 g/L resulted in a positive predictive value of 38% (95% CI: 24–52%) but lowered the sensitivity to 15% (95% CI: 7–22%). Conclusions. ID remains common in the United States. In agreement with other reports, anemia in toddlers in developed countries is more likely to be due to causes other than ID. Conversely, most children with ID are not anemic. Many false-positive and false-negative results render the measurement of Hb a screening test of relatively little value. The current detection strategy needlessly treats and retests many children without ID and leaves many iron-deficient toddlers unattended.