Published online July 3, 2006
PEDIATRICS Vol. 118 No. 1 July 2006, pp. 224-232 (doi:10.1542/peds.2006-0156)
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Comparative Effectiveness of Zinc Protoporphyrin and Hemoglobin Concentrations in Identifying Iron Deficiency in a Group of Low-Income, Preschool-Aged Children: Practical Implications of Recent Illness

Rebecca Crowell, PhDa, Ann M. Ferris, PhD, RDa,b, Richard J. Wood, PhDc, Patricia Joyce, MDd and Hilda Slivka, MDd

a Department of Nutritional Sciences
b Center for Public Health and Health Policy, University of Connecticut, Storrs, Connecticut
c Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, Massachusetts
d Department of Pediatrics, University of Connecticut School of Medicine, Farmington, Connecticut

OBJECTIVE. The goal was to assess the influence of recent infection on screening tests for iron depletion (zinc protoporphyrin and hemoglobin) among low-income, preschool-aged children.

METHODS. This cross-sectional study was conducted at community sites and ambulatory care clinics in Hartford, Connecticut, and included 180 preschool-aged children. Iron depletion was defined as serum ferritin levels of ≤15 µg/L. Recent illness was defined by parent or guardian (caretaker) report or evidence of elevated C-reactive protein concentrations. History of anemia was determined through medical records review. Sensitivity, specificity and positive predictive values of hemoglobin and zinc protoporphyrin were calculated overall and for children with and without recent illness.

RESULTS. At enrollment, more than one half of the children had a recent illness, and 57.5% had a history of anemia. More than one third had iron depletion. Serum ferritin levels were significantly higher among recently ill children. Secondary to recent illness, the positive predictive value of elevated zinc protoporphyrin, but not low hemoglobin, was reduced significantly. Zinc protoporphyrin levels of >69 µmol/mol heme identified significantly more iron-deficient children.

CONCLUSIONS. Compared with anemia, elevated zinc protoporphyrin levels identified significantly more iron-deficient children. Recently ill children were one half as likely to have low serum ferritin levels, compared with children without recent illness. The negative effect of recent illness on the positive predictive value of zinc protoporphyrin when ferritin is used to determine iron status has many practical implications.

Key Words: anemia • iron deficiency • zinc protoporphyrin • preschool-aged child

Abbreviations: PPV—positive predictive value • ZPP—zinc protoporphyrin • CDC—Centers for Disease Control and Prevention • WIC—Special Supplemental Food Program for Women—Infants—and Children • CI—confidence interval • OR—odds ratio • CRP—C-reactive protein • TfR—transferrin receptor

Accepted Feb 15, 2006.