Published online July 3, 2006
PEDIATRICS Vol. 118 No. 1 July 2006, pp. 224-232 (doi:10.1542/peds.2006-0156)
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow P3Rs: Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when P3Rs are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow E-mail this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My File Cabinet
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via ISI Web of Science (5)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Crowell, R.
Right arrow Articles by Slivka, H.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Crowell, R.
Right arrow Articles by Slivka, H.
Related Collections
Right arrow Blood

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


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
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

epercussions of nutritional iron deficiency among young children include deficits in cognitive, emotional, and psychomotor development.1–4 Although negative outcomes warrant early detection and treatment, identification of iron deficiency is challenging. In the case of low-income children <5 years of age, guidelines for the prevention and control of iron deficiency call for routine hemoglobin screening.5–7 A recent analysis of data from the Third National Health and Nutrition Examination Survey found that hemoglobin measurements lacked sensitivity and exhibited poor positive predictive value (PPV) for iron deficiency among 1- to 3-year-old children.8 Hemoglobin levels become abnormally low only late in iron deficiency and may also be influenced by heredity or overall health status.6 Among young children, who may have between 6 and 12 colds each year, infection is considered the most common cause of anemia after iron deficiency.9

The zinc protoporphyrin (ZPP)/heme ratio may overcome some disadvantages of hemoglobin screening. Although hemoglobin levels represent one of the last indicators of iron deficiency, elevated ZPP levels are an indication of iron-deficient erythropoiesis.10–12 Therefore, ZPP has shown promise as an iron status indicator in clinical and research settings.10–17 Assessment is rapid and requires only 1 or 2 drops of capillary whole blood and a portable hematoflurometer.12,18 However, as an indicator of iron-deficient erythropoiesis in response to iron insufficiency, ZPP levels may be influenced by other conditions that affect red blood cell production and heme biosynthesis, including lead toxicity, chronic infection, inflammation, hyperbilirubinemia, and hemoglobinopathies.14,19,20 Washing erythrocytes to remove plasma components before assessment may reduce the number of false-positive tests,21 although the additional steps may limit the convenience of ZPP measurements in outpatient or field settings. Nonetheless, ZPP is considered a highly specific indicator of erythropoietic iron supply, and levels are not influenced directly by acute infection.10–15

Low serum ferritin levels are the earliest indication of low body iron stores. Therefore, this measurement is used frequently to confirm iron deficiency in clinical practice or research settings. Unfortunately, serum ferritin is an acute-phase protein, and levels become elevated during infection or inflammation. The effects of infection on serum ferritin levels may last for >15 days after exposure.22,23 Serum soluble transferrin receptor (TfR) measurements have been shown to be a good indication of iron deficiency-induced erythropoiesis.24 In addition, the ratio of ferritin to TfR has been suggested as a useful measure of body iron stores.25,26

The goal of this research was to compare the effectiveness of hemoglobin and ZPP measurements as point-of-service screening tests for iron deficiency among low-income preschool-aged children in Hartford, Connecticut. We also assessed the degree to which recent illness influenced the PPV, sensitivity, and specificity of the screening tests. We hypothesized that elevated ZPP levels measured in unwashed red blood cells would be a better indicator of iron deficiency, compared with low hemoglobin levels, in this high-risk population of poor, inner-city children.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Study Population
Data were collected at sites throughout Hartford, Connecticut. Nearly two thirds of children <5 years of age in that city reside in low-income households.27,28 Anemia is common; as many as 1 in 3 children in Hartford become anemic at least once between the ages of 18 months and 3 years.29 As is typical in the United States, anemia is identified and addressed through primary care health providers and the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). WIC recertification requires that children be screened regularly for anemia.

Human Subjects
The protocol was approved by internal review boards at the University of Connecticut, Connecticut Children's Medical Center, St Francis Hospital, and Tufts University. Parents or guardians (caretakers) provided informed consent at the time of enrollment; all forms and information (written and oral) were provided in English or Spanish, depending on the caretaker's preference.

Subject Enrollment and Eligibility
Subjects were recruited between January 2002 and March 2004, at family resource centers, child care centers, and social service agencies offering nutrition education and free screening for anemia and elevated ZPP levels. Screening results were forwarded to primary care providers for use at the child's next health visit. Sites for the screening program were selected to match the ethnicity, poverty level, and social capital score30 of neighborhood school districts. Eligible children were between 18 months and 60 months of age at the time of enrollment, resided within the greater Hartford area, and did not have a febrile illness at the time of enrollment, according to caretaker report.

Demographic and Health Data
In addition to information pertaining to ethnicity, income, and receipt of WIC and food stamp benefits, each caretaker was asked about the child's illness history in the previous month, whether the child had been given medication in the previous week, whether the child was being treated for anemia or had been give vitamins in the previous week, and whether the child was being treated or monitored for lead toxicity at the time of enrollment.

History of Anemia
History of anemia was determined through medical records review, coinciding with ongoing anemia surveillance. Caretakers were asked to sign a release for review of medical records and, after April 14, 2003, were also asked to sign a release specific to the Health Insurance Portability and Accountability Act. Data pertaining to visit type, diagnoses, anthropometric measurements, and laboratory tests were extracted for each visit from birth onward. Extracted data were then compared against the original chart. History of anemia was assessed with screening hemoglobin, hematocrit, or complete blood count results obtained at either well-child check-ups or WIC recertification. Laboratory data from emergency department, preoperative, or "sick" visits were excluded.

Sample Collection and Analysis
Capillary blood was used for biochemical analyses. Children who seemed overly fearful or uncomfortable with the procedure (n = 4) were not tested. A pediatric nurse obtained capillary blood from each child's right index or middle finger, after wiping away the first 2 large drops of blood. Capillary blood was tested immediately for hemoglobin with a hemoglobinometer (HemoCue, Lake Forest, CA) and for ZPP with a hematofluorometer (AVIV Biomedical, Lakewood, NJ). Before each 2-hour screening session, instruments were assessed with control samples supplied by the manufacturers.

For biochemical analysis, 60 to 90 µL of blood were collected, stored on ice, and transported to the University of Connecticut within 2 hours. Serum was harvested through centrifugation and was stored at –80°C. Frozen samples were transported on dry ice to the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University for analysis of serum ferritin levels (Diagnostic Products Corp, Los Angeles, CA), TfR levels (Ramco Laboratories, Stafford, TX), and C-reactive protein (CRP) levels (Equal Diagnostics, Exton, PA). Samples were small, and duplicate assays were performed when feasible. Assessment of serum ferritin levels was given highest priority, followed by CRP and TfR levels. Of the 241 children enrolled initially in this study, 180 had complete values for hemoglobin, ZPP, and serum ferritin levels and were included in the analysis.

Prioritization allowed for assessment of TfR levels for a subsample of 74 children. TfR concentration is not used widely in clinical or outpatient settings. However, TfR is upregulated during iron-deficient erythropoiesis and remains stable during infection.31

Assessment of Iron Status
Anemia was defined with Centers for Disease Control and Prevention (CDC) guidelines (<24 months of age, hemoglobin level of <110 g/L; 24–60 months of age, <111 g/L).5 ZPP levels of >69 µmol/mol heme were considered indicative of iron depletion. The moderate cutoff point is consistent with data pertaining to ZPP levels of >10th percentile for children of similar age.32

Serum ferritin levels of ≤15 µg/L were used as an indication of reduced iron stores.5 Although cutoff points as low as 10 to 12 µg/L are used in population surveys,33 the higher cutoff point was chosen to identify children who might benefit from intervention and because of its similarity to the cutoff point of <15 µg/L recommended by the American Academy of Pediatrics to confirm iron deficiency among anemic children.6 Because reference standards for children have not been established firmly, TfR levels were considered elevated at values of >8.3 µg/mL, according to the assay manufacturer's specifications. Several studies indicated that TfR values for infants and young children might be slightly higher than those used for adults,25,34–38 but data were inconsistent because of variations in the ages of the subjects and the assays used in analyses. CRP levels were considered elevated at >5 mg/L.39–41

Illness Status
Recent illness was defined as an affirmative response to the question, "Has your child been ill in the past 30 days?" or an affirmative response to the question, "Has your child received medication for illness in the past week?" If the caretaker did not answer either question in the affirmative but CRP levels were elevated, then the child was included in the recently ill group. As noted above, any child with a febrile illness on the day of enrollment was excluded from the study. Peak illness season was defined as the months of November through February.

Statistical Analyses
Statistical analyses were performed with SAS version 9.0 for Windows (SAS Institute, Cary, NC). Two age categories were used, namely, 18 months to <3 years of age and 3 to 5 years of age. Income was assessed with 2003 federal poverty guidelines for reported income or as an affirmative answer to receipt of food stamp or WIC benefits. Because the majority of subjects were either black or Latino, comparisons based on ethnicity focused on these 2 groups.

PPV was calculated for hemoglobin and ZPP by dividing the number of iron-deficient subjects who had positive screening results by the total number of positive screens. Sensitivity was calculated by dividing the number of iron-deficient subjects identified by the test by the total number of iron-deficient subjects. Similarly, specificity was determined by dividing the number of screens excluding iron deficiency correctly by the total number of iron-sufficient subjects. Children undergoing treatment for anemia at the time of enrollment were excluded from analyses of PPV, sensitivity, and specificity.

Distributions of biochemical indices were assessed with probability plots. Descriptive statistics were assessed for normally distributed indices (hemoglobin) with Student's t test and for non-normally distributed indices (ZPP, ferritin, and TfR) with the nonparametric Wilcoxon rank-sum statistic. Categorical data were analyzed with the Pearson {chi}2 test and backward-elimination logistic regression. Finally, the effectiveness of ZPP and anemia relative to identification of iron deficiency was compared with McNemar's test, a test of paired proportions. P values of <.05 were considered significant. Unless otherwise noted, 2-tailed tests of significance were used.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Sample Characteristics
Children had a mean age of 3.2 years. Most were WIC-eligible, on the basis of reported income or receipt of benefits, and were either black or Latino (Table 1). Ten children had a history of blood lead levels of >9 µg/dL, on the basis of parental reports or medical records review. Approximately one half of the sample had evidence of recent illness at enrollment (Table 1). Parental reports of medication given for illness in the previous week (alone or in combination) included over-the-counter cold medicine (31%), over-the-counter pain relievers (24%), antibiotics (19%), and prescription asthma medication (19%). Anemia was common in this group of children. Of 120 children with accessible medical records, more than one half had been anemic, on the basis of CDC guidelines for hemoglobin or hematocrit levels, at least once during a well-child check-up or WIC recertification visit (Table 2). Of the 69 children who were ever anemic (on the basis of medical records), 62 (89.9%) were anemic at least once between 1 and 3 years of age. On the basis of information in the medical charts, most screening assessments (73%) were made with venous blood drawn in a hospital laboratory.


View this table:
[in this window]
[in a new window]
  		TABLE 1 Characteristics of 18- to 60-Month-Old Participants From Hartford, Connecticut

 

View this table:
[in this window]
[in a new window]
  		TABLE 2 Hematologic Parameters

 
Anemia and Iron Status
Anemia and poor iron status were common in this group of children. Thirty-four children (18.8%) were anemic or were being treated for anemia by a primary care physician at the time of enrollment. More than one third of the overall sample had low serum ferritin levels, and 30% had elevated ZPP levels (Table 2). Iron-deficiency anemia (serum ferritin levels of ≤15 µg/L and anemia) was evident for 5% of the children, and iron deficiency with elevated ZPP levels (serum ferritin levels of ≤15 µg/L and ZPP levels of >69 µmol/mol heme) was evident for 11.7% (Table 2). The risk of iron deficiency was influenced by ethnicity, age, and socioeconomic factors. Children who were younger, Latino, living in low-income households, or residing with a caretaker with less than a high school education were significantly more likely to have iron deficiency (Table 3). A history of elevated blood lead levels (>9 µg/dL) was not associated with lower hemoglobin levels, higher ZPP levels, or higher TfR levels, although the 10 children with a history of elevated blood lead levels tended to have lower serum ferritin values (P < .08, Wilcoxon rank-sum test), with a significantly greater number of serum ferritin values below the sample median (P < 0 .05, median test).


View this table:
[in this window]
[in a new window]
  		TABLE 3 Relative Risk of Iron Deficiency Among Preschool-Aged Children From Hartford, Connecticut

 
Recent Illness and Iron Status
No significant differences were found between children with and without recent illness with respect to age, gender, ethnicity, income, or caretaker's level of education. Season had a significant effect on illness presentation. Children enrolled between the months of November and February were 87% more likely than children enrolled between March and October to have had a recent illness (odds ratio [OR]: 1.87; 95% confidence interval [CI]: 1.20–3.35; P < .04). Nearly 60% (57.9%) of children enrolled during months categorized as the peak illness season had evidence of recent illness, compared with 42.4% of children enrolled at other times of the year.

With the exception of serum ferritin levels, recent illness had no significant effect on laboratory parameters (Table 4). Recently ill children were one half as likely to have low serum ferritin levels (OR: 0.522; 95% CI: 0.28–0.98; P = .041). No significant differences were found in hematologic parameters or proportions of children with abnormal laboratory values on the basis of the time of year. Caretakers of recently ill children were more likely to report giving their children vitamins in the week before enrollment (35.2% vs 15.7%; OR: 2.91; 95% CI: 1.42–5.94; P < .003). PPVs for hemoglobin and ZPP were higher among children without recent illness (Fig 1). The effect of recent illness on the PPVs of screening tests for iron deficiency was most pronounced with respect to ZPP. After controlling for age and ethnicity, the interaction between illness and ZPP levels was significant (Fig 1). Recent illness reduced the overall sensitivity of ZPP by one third but had minimal effect on hemoglobin (Table 5).


View this table:
[in this window]
[in a new window]
  		TABLE 4 Iron Status Among Recently Ill Versus Not Recently Ill Preschool-Aged Children From Hartford

 

Figure 1
View larger version (13K):
[in this window]
[in a new window]
  		FIGURE 1 PPVs of screening tests relative to iron deficiency, according to illness history (excludes 22 children who were being treated for anemia at the time of enrollment). aSignificant interaction between screening test and recent illness (P < .005), after controlling for age and ethnicity (logistic regression model).

 

View this table:
[in this window]
[in a new window]
  		TABLE 5 Sensitivity and Specificity of Screening Tests According to Illness Status

 
ZPP measurements identified many more iron-deficient children than did hemoglobin measurements (Fig 2). After exclusion of children being treated for anemia (n = 22), 19 of 53 iron-deficient children were identified with hemoglobin or ZPP measurements. Only 13 were identified with ZPP values alone and just 4 with hemoglobin results alone. Only 2 iron-deficient subjects would have been identified if both abnormal ZPP and hemoglobin results had been used as screening tests. Among children with recent illness, low hemoglobin levels identified 3 with iron deficiency and elevated ZPP levels identified 2 (Fig 2).


Figure 2
View larger version (10K):
[in this window]
[in a new window]
  		FIGURE 2 Numbers of iron-deficient children identified with screening tests (excludes 22 children who were undergoing treatment for anemia at the time of enrollment). Hb indicates hemoglobin. aMcNemar's test, P < .03; bMcNemar's test, P < .004.

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Iron deficiency among young children is a serious concern, because a growing body of research has documented an association between iron deficiency in early childhood and developmental deficits.1,3,42,43 This association may extend to educational underachievement.2,44 In addition, iron deficiency among young children has been associated with subsequent lead toxicity.45

An important finding of this study is that more than one third of the preschool-aged children enrolled in this study had low iron stores, which attests to the persistence of this nutritional problem. Although the study design might have led to self-selection (and thus overenrollment) of anemic children, recent surveillance in a representative random sample of children in Hartford, Connecticut, found that more than one half were anemic at least once, primarily between 12 and 36 months of age (A.M.F., unpublished data, 2004). The surveillance used medical chart review and was conducted as a follow-up study to initial research documenting a 33% occurrence of anemia among Hartford toddlers 18 to 36 months of age.29

In the current study, we found that the risk of iron deficiency was increased with younger age, lower socioeconomic status, and Latino ethnicity. Although small in number, the children in our study with histories of lead toxicity tended to be at greater risk for iron deficiency. Early intervention with iron supplementation could prevent the development of iron-deficiency anemia and might reduce the risk of lead toxicity in this high-risk population of iron-deficient children. Depleted iron stores for these low-income children likely place them at greater risk for negative health and developmental outcomes, which warrants additional efforts at early detection and prevention.

A second important finding of this study is that a simple, inexpensive, point-of-service ZPP screening test with unwashed erythrocytes identified significantly more iron-deficient children than did hemoglobin measurements. Presumably, the subjects with elevated ZPP levels would be candidates for iron supplementation to prevent additional deterioration of iron status and the development of iron-deficiency anemia.

Our observation is consistent with other studies showing that ZPP measurements improve identification of iron deficiency, compared with hemoglobin or hematocrit measurements.16,17 We also demonstrated that infection within 1 month before assessment had a profound negative impact on the effectiveness of ZPP measurement as a screening test. This result is most likely attributable to our use of measurement of serum ferritin, an acute-phase reactant, as a standard method for assessment for iron deficiency. Although our definition of recent illness might in part rely on caretaker interpretation and memory (thus causing us to misclassify some recently ill children in the "well" group), this characterization is strengthened by a 3-tiered classification coupled with significant group differences in serum ferritin levels. The increase in serum ferritin levels in response to recent illness warrants caution when that indicator is used to interpret ZPP results. This problem is particularly evident in this group of children, more than one half of whom had evidence of recent illness at enrollment in the study. Although the relationship between ferritin levels and infection is well known, we suspect that many children who are screened frequently for iron deficiency are not assessed with respect to illness history.

Unacceptable sensitivity and specificity of screening tests may limit early identification of iron deficiency. The US Preventive Services Task Force (USPSTF) uses the following criteria to assess the effectiveness of preventive screening: a test must be sensitive enough to identify a large proportion of individuals with a given condition while being specific enough to rule out the condition in a large percentage of healthy individuals, the test must be reliable, and early detection of a condition or illness through screening must be associated with patient benefit.46

We found that, in our sample of children, the specificity of hemoglobin measurement as a screening test for iron deficiency was quite high (Table 5); the test identified correctly ~94% of children with normal iron stores. Recent illness tended to improve the sensitivity of hemoglobin measurement, most likely by causing enough of a decline in the hemoglobin concentrations of iron-deficient, nonanemic children to place those children in the anemic category. As expected, however, the sensitivity of hemoglobin measurement was low; the test identified correctly only 11% of iron-deficient subjects. Therefore, use of hemoglobin measurement alone as a screening test for iron deficiency, as practiced currently by WIC, would fail to identify 9 of 10 iron-deficient children. This rate of misclassification seems unacceptably high, given the poor developmental outcomes associated with iron deficiency among young children. These findings from our study of poor, inner-city, minority children are consistent with a recent analysis of data from the Third National Health and Nutrition Examination Survey, which found that hemoglobin measurement lacked sensitivity and exhibited a poor PPV, with respect to iron deficiency, among 1- to 3-year-old children.8

ZPP measurement was a more-sensitive test for iron deficiency than was hemoglobin measurement. Overall, with a ZPP cutoff value of >69 µmol/mol heme in unwashed red blood cells, we identified correctly 2.5 times (sensitivity of 28%, compared with 11%) as many iron-deficient children as when we used the current testing standard based on the CDC anemia cutoff value for hemoglobin levels. However, our data indicated that the performance of ZPP measurements was markedly poorer in the group with recent illness. Among children identified as recently ill (approximately one half of the subjects), ZPP measurement performed as poorly (sensitivity of 10%) as did hemoglobin measurement in detecting iron-deficient subjects. However, under these conditions, the observed sensitivity might have underestimated the true sensitivity of the ZPP test. This is because serum ferritin levels, our criterion for iron deficiency, likely increased independent of changes in body iron stores among subjects in the recently ill group, which would result in the misclassification of truly iron-deficient subjects. The extent of this possible misclassification is unknown but would be expected to reduce the apparent sensitivity of screening tests. This notion is supported by the observation that, when the ZPP screening test was limited to children without recent illness (primarily on the basis of a simple oral report from the caretaker), performance was remarkably better. Among healthy children, we found that nearly 40% of iron-deficient children were correctly identified with the ZPP test.

It is evident that, in a population of healthy young children, the ZPP screening test is much superior to hemoglobin measurement as a means to identify children with iron deficiency. Therefore, it seems prudent to include this measure in the screening protocols for the early detection of iron deficiency among young children. Because of the diversity of serious conditions causing iron-deficient erythropoiesis and therefore ZPP changes, increases in ZPP levels should be considered clinically significant.11,12,20

However, adherence to screening guidelines often depends on clinician attitudes, motivations, beliefs, and experience.47,48 A test that performs poorly or seems ineffective in practice may influence negatively the motivation to treat.48 Because elevated ZPP levels indicate a nonspecific disruption in the iron supply for erythropoiesis, follow-up testing to confirm iron deficiency or to rule out lead toxicity is warranted. In discussions with health personnel involved in this study, we were told that some of the reluctance in using the ZPP test as a screening tool for iron deficiency, compared with determination of anemia (low hemoglobin levels) alone, was that ZPP measurement had low specificity and would result in the false identification of many subjects who actually were not iron deficient. A positive ZPP test would lead to additional confirmatory testing (eg, serum ferritin measurement) and an unnecessary added burden for both the patient and the health care system of additional follow-up visits and additional associated costs. The belief by the health care professionals that ZPP measurement would identify incorrectly as iron deficient more children with normal iron status is supported by our findings. We observed that the overall sensitivity of ZPP measurement in this population was 0.72 (compared with 0.94 for hemoglobin). Therefore, the false-positive rate with the established hemoglobin cutoff value would be only 6% (~1 of every 10 children with normal iron status tested), whereas the false-positive rate for ZPP measurement would be 28% (~3 of every 10 normal children tested). A policy decision would need to be considered in these health care settings, namely, whether the burden of additional follow-up testing imposed on an additional 2 of every 10 children with normal iron status counterbalances the positive effect of correctly identifying twice as many iron-deficient children.

Management of iron deficiency is difficult in populations in which adherence to treatment plans and follow-up monitoring are poor.49 If ZPP measurement is to be used as a point-of-service screen for iron deficiency, then protocols for diagnosis, treatment, and management must be refined. For instance, the question of whether intensive dietary counseling in response to elevated ZPP levels could prevent anemia and improve iron status warrants additional research. It should be noted that, given the high prevalence of illness in this study population, attempts by health professionals to confirm the ZPP classification of iron deficiency for recently ill children with serum ferritin measurement would underestimate the number of truly iron-deficient subjects and reinforce the belief that ZPP measurement has unacceptably low sensitivity and specificity. The marked decreases in sensitivity and specificity of ZPP measurement among recently ill children tend to confirm this idea. Because of the acute-phase response, ferritin levels can remain significantly elevated weeks after the onset of illness.50 Because we did not assess changes in ZPP or hemoglobin levels with a therapeutic trial of iron, we cannot say definitively that these children had functional iron deficiency. Serum TfR is an index of iron deficiency that is not affected by infection or inflammation24,25 and might have served as a better index of iron deficiency among ill children. Unfortunately, we were unable to measure TfR levels for a large number of subjects, because of the small volume of capillary blood obtained from each subject. From a practical point of view, iron status assessment should be deferred until the child is well, or illness history in the past month (based on parent report) should be taken into account during clinical assessment, even if a child seems well at the time of screening.


   ACKNOWLEDGMENTS
 
The project was supported by the National Research Initiative of the US Department of Agriculture Cooperative State Research, Education, and Extension Service (grant 2002-35200-12227).

We thank Dorothy Wakefield, MS, at the University of Connecticut for help with statistical analysis, Bruce Bernstein, PhD, at St Francis Hospital for advice on study implementation and Renee Richard, RN, and the University of Connecticut Husky Anemia Project staff members for assistance with data collection and outreach. We owe a debt of gratitude to study participants and their caretakers.


   FOOTNOTES
 
Accepted Feb 15, 2006.

Address correspondence to Rebecca Crowell, PhD, Department of Nutritional Sciences, University of Connecticut, Unit 4017, 3624 Horsebarn Rd Extension, Storrs, CT 06269. E-mail: rebecca.crowell{at}hotmail.com

The authors have indicated they have no financial relationships relevant to this article to disclose.


   REFERENCES
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. DeAndraca I, Castillo M, Walter T. Psychomotor development and behavior in iron-deficient anemic infants. Nutr Rev. 1997;55 :125 –132[ISI][Medline]
  2. Lozoff B, Jimenez E, Hagen J, Mollen E, Wolf A. Poorer behavioral and developmental outcome more than 10 years after treatment for iron deficiency in infancy. Pediatrics. 2000;105 (4). Available at: www.pediatrics.org/cgi/content/full/105/4/e51
  3. Lozoff B, Klein N, Nelson E, McClish D, Manuel M, Chacon ME. Behavior of infants with iron-deficiency anemia. Child Dev. 1998;69 :24 –36[CrossRef][ISI][Medline]
  4. Lozoff B, Wolf A, Urrutia J, Viteri F. Abnormal behavior and low developmental test scores in iron-deficient anemic infants. J Dev Behav Pediatr. 1985;6 :69 –75[ISI][Medline]
  5. Centers for Disease Control and Prevention. Recommendations to prevent and control iron deficiency in the United States. MMWR Recomm Rep. 1998;47 (RR-3):1 –29[Medline]
  6. American Academy of Pediatrics, Committee on Nutrition. Iron deficiency. In: Kleinman RE, ed. Pediatric Nutrition Handbook. 5th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2003:299 –311
  7. Green M, Palfrey J, eds. Bright Futures: Guidelines for Health Supervision of Infants, Children, and Adolescents. 2nd ed, rev ed. Arlington, VA: National Center for Education and Maternal and Child Health; 2002
  8. White KC. Anemia is a poor predictor of iron deficiency among toddlers in the United States: for heme the bell tolls. Pediatrics. 2005;115 :315 –320[Abstract/Free Full Text]
  9. Abshire T. The anemia of inflammation: a common cause of childhood anemia. Pediatr Clin North Am. 1996;43 :623 –637[CrossRef][ISI][Medline]
  10. Hastka J, Lasserre J-J, Schwarzbeck A, Hehlmann R. Central role of zinc protoporphyrin in staging iron deficiency. Clin Chem. 1994;40 :768 –773[Abstract/Free Full Text]
  11. Labbe R, Dewanji A, McLaughlin K. Observations on the zinc protoporphyrin/heme ratio in whole blood. Clin Chem. 1999;45 :146 –148[Free Full Text]
  12. Rettmer R, Carlson T, Origenes M, Jack R, Labbe R. Zinc protoporphyrin/heme ratio for diagnosis of preanemic iron deficiency. Pediatrics. 1999;104 :104 –107
  13. Hastka J, Lasserre JJ, Schwarzbeck A, Reiter A, Hehlmann R. Laboratory tests of iron status: correlation or common sense? Clin Chem. 1996;42 :718 –724[Medline]
  14. Hinchliffe R, Lilleyman J, Steel G. Usefulness of red cell zinc protoporphyrin concentrations in the investigation of microcytosis in children. Pediatr Hematol Oncol. 1995;12 :455 –462[ISI][Medline]
  15. Labbe R, Dewanji A. Iron assessment tests: transferrin receptor vis-a-vis zinc protoporphyrin. Clin Chem. 2004;37 :165 –174
  16. Siegel R, LaGrone D. The use of zinc protoporphyrin in screening young children for iron deficiency. Clin Pediatr (Phila). 1994;33 :473 –479[Abstract/Free Full Text]
  17. Mei Z, Parvanta I, Cogswell M, Gunter E, Grummer-Strawn L. Erythrocyte protoporphyrin or hemoglobin: which is a better screening test for iron deficiency in children and women? Am J Clin Nutr. 2003;77 :1229 –1233[Abstract/Free Full Text]
  18. Beutler E, Hoffbrand AV, Cook JD. Iron deficiency and overload. Hematology (Am Soc Hematol Educ Program). 2003:40 –61
  19. Hastka J, Lasserre J-J, Schwarzbeck A, Strauch M, Hehlmann R. Zinc protoporphyrin in anemia of chronic disorders. Blood. 1993;81 :1200 –1204[Abstract/Free Full Text]
  20. Graham E, Felgenhauer J, Detter J, Labbe R. Elevated zinc protoporphyrin associated with thalassemia trait and hemoglobin E. J Pediatr. 1996;129 :105 –110[CrossRef][ISI][Medline]
  21. Hastka J, Lasserre J, Schwarzbeck A, Strauch M, Hehlmann R. Washing erythrocytes to remove interferents in measurements of zinc protoporphyrin by front-face hematofluorometry. Clin Chem. 1992;38 :2184 –2189[Abstract/Free Full Text]
  22. Sipahi T, Koksal T, Tavil B, Akar N. The effects of acute infection in hematological parameters. Pediatr Hematol Oncol. 2004;21 :513 –520[ISI][Medline]
  23. Olivares M, Walter T, Osorio M, Chadud P, Schlesinger L. Anemia of mild viral infection: the measles vaccine as a model. Pediatrics. 1989;84 :851 –855[Abstract/Free Full Text]
  24. Beguin Y. Soluble transferrin receptor for the evaluation of erythropoiesis and iron status. Clin Chim Acta. 2003;329 :9 –22[CrossRef][ISI][Medline]
  25. Olivares M, Walter T, Cook J, Hertrampf E, Pizarro F. Usefulness of serum transferrin receptor and serum ferritin in diagnosis of iron deficiency in infancy. Am J Clin Nutr. 2000;72 :1191 –1195[Abstract/Free Full Text]
  26. Punnonen K, Irjala K, Rajamaki A. Serum transferrin receptor and its ratio to serum ferritin in the diagnosis of iron deficiency. Blood. 1997;89 :1052 –1057[Abstract/Free Full Text]
  27. Bishaw A, Iceland J. Poverty 1999: Census 200 Brief Washington, DC: US Census Bureau; 2003
  28. Schack B. Hartford Series: Neighborhood Revitalization Zone Census Profile from the US Census. Hartford, CT: Citizens' Research Education Network; 2004
  29. Moran D, Ferris A, Campbell M, et al. Anemia among 18- to 36-month-old children in Hartford, CT. FASEB J. 1999;13 :A698
  30. Martin K, Rogers B, Cook J, Joseph H. Social capital is associated with decreased risk of hunger. Soc Sci Med. 2004;58 :2645 –2654[CrossRef][ISI][Medline]
  31. Baynes R. Assessment of iron status. Clin Biochem. 1996;29 :209 –215[CrossRef][ISI][Medline]
  32. Soldin OP, Pezzullo J, Hanak B, Miller M, Soldin S. Changing trends in the epidemiology of pediatric lead exposure: interrelationship of blood lead and ZPP concentrations and a comparison to the US population. Ther Drug Monit. 2003;25 :415 –420[CrossRef][ISI][Medline]
  33. Looker A, Dallman P, Carroll M, Gunter E, Johnson C. Prevalence of iron deficiency in the United States. JAMA. 1997;277 :973 –976[Abstract]
  34. Choi JW, Pai SH, Im MW, Kim SK. Change in transferrin receptor concentrations with age. Clin Chem. 1999;45 :1562 –1563[Free Full Text]
  35. Schneider J, Fujii M, Lamp C, Lonnerdal B, Dewey K, Zidenberg-Cherr S. Anemia, iron deficiency and iron deficiency anemia in 12- to 36-month-old children from low-income families. Am J Clin Nutr. 2005;82 :1269 –1275[Abstract/Free Full Text]
  36. Suominen P, Virtanen A, Lethonin-Veromaa M, et al. Regression-based reference limits for serum transferrin receptor in children 6 months to 16 years of age. Clin Chem. 2001;47 :935 –937[Free Full Text]
  37. Virtanen M, Viinikka L, Virtanen M, et al. Higher concentrations of serum transferrin receptor in children than in adults. Am J Clin Nutr. 1999;69 :256 –260[Abstract/Free Full Text]
  38. Zimmermann M, Molinari L, Staubli-Asobayire F, et al. Serum transferrin receptor and zinc protoporphyrin as indicators of iron status in African children. Am J Clin Nutr. 2005;81 :615 –623[Abstract/Free Full Text]
  39. Sankaranarayanan S, Untoro J, Erhardt J, Gross R. Daily iron alone but not in combination with multimicronutrients increases plasma ferritin concentrations in Indonesian infants with inflammation. J Nutr. 2004;134 :1916 –1922[Abstract/Free Full Text]
  40. Thomas C, Thomas L. Biochemical markers and hematologic indices in the diagnosis of functional iron deficiency. Clin Chem. 2002;48 :1066 –1076[Abstract/Free Full Text]
  41. Thompson D, Milford-Ward A, Whicher J. The value of acute phase protein measurements in clinical practice. Ann Clin Biochem. 1992;29 :123 –131[Medline]
  42. Idjradinata P, Pollitt E. Reversal of developmental delays in iron-deficient anaemic infants treated with iron. Lancet. 1993;341 :1 –4[CrossRef][ISI][Medline]
  43. Lozoff B, Wolf A, Jimenez E. Iron-deficiency anemia and infant development: effects of extended oral iron therapy. J Pediatr. 1996;129 :382 –389[CrossRef][ISI][Medline]
  44. Hurtado E, Claussen A, Scott K. Early childhood anemia and mild or moderate mental retardation. Am J Clin Nutr. 1999;69 :115 –119[Abstract/Free Full Text]
  45. Wright R, Tsaih S-W, Schwartz J, Wright R, Hu H. Association between iron deficiency and blood lead level in a longitudinal analysis of children followed in an urban primary care clinic. J Pediatr. 2003;142 :9 –14[CrossRef][ISI][Medline]
  46. US Preventive Services Task Force. Guide to Clinical Preventive Care. 2nd ed. Washington, DC: Office of Disease Prevention and Health Promotion; 1996
  47. Cabana M, Rand C, Powe N, et al. Why don't physicians follow clinical practice guidelines? A framework for improvement. JAMA. 1999;282 :1458 –1465[Abstract/Free Full Text]
  48. Crowell R, Pierce M, Ferris A, et al. Managing anemia in low-income toddlers: barriers, challenges and context in primary care. J Health Care Poor Underserved. 2005;16 :791 –807[ISI][Medline]
  49. Crowell R, Ferris A, Wood R, Wakefield D. Household participation in food benefit programs differentially affects iron status indicators in low-income preschoolers. FASEB J. 2005;19 :A1697 –A1698
  50. Reeves J, Yip R, Kiley V, Dallman P. Iron-deficiency in infants: the influence of mild antecedent infection. J Pediatr. 1984;105 :874 –879[CrossRef][ISI][Medline]
PEDIATRICS (ISSN 1098-4275). ©2006 by the American Academy of Pediatrics




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow P3Rs: Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when P3Rs are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow E-mail this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My File Cabinet
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via ISI Web of Science (5)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Crowell, R.
Right arrow Articles by Slivka, H.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Crowell, R.
Right arrow Articles by Slivka, H.
Related Collections
Right arrow Blood