Objectives. To estimate the proportion of children 1 to 5 years of age who received blood lead testing during 1988–1994 and to assess whether predictors of testing coincided with predictors of elevated blood lead levels.
Design. Cross-sectional analysis of data from the Third National Health and Nutrition Examination Survey.
Participants. US children 1 to 5 years of age.
Outcome Measures. Prevalence of blood lead testing and elevated blood lead levels among children 1 to 5 years of age and odds ratios for factors predicting blood lead testing and elevated blood lead levels.
Results. Overall, 6.3% had elevated blood lead levels and 10.2% had undergone previous blood lead tests. Being of minority race/ethnicity, living in an older home, residing in the Northeast or Midwest regions of the United States, being on Medicaid, having a head of household with <12 years of education, and having a history of anemia were significant factors in both models. Additional independent risk factors for an elevated blood lead level included being sampled in phase 1 of the survey, being 1 to 2 years of age, not having a regular doctor, and being sampled during the summer months. Additional independent correlates of a previous blood lead test included having moved less than twice in one's lifetime, having a female head of household, and having parents whose home language was English. Of an estimated 564 000 children 1 to 5 years of age who had elevated blood lead levels and no previous screening test in 1993, 62% were receiving Medicaid, 40% lived in homes built before 1946, and 34% were black, non-Hispanic.
Conclusions. Lead screening was more frequent among children with risk factors for lead exposure. However, among children with elevated blood lead levels, only one third had been tested previously. In 1993 an estimated 564 000 children 1 to 5 years of age had elevated blood lead levels but were never screened. Physicians should screen Medicaid-eligible children and should follow state or local health department recommendations about identifying and screening other at-risk children. In areas where no health department guidelines exist, physicians should screen all children or screen based on known risk factors.
According to the most recently available national data, nearly 900 000 preschool-aged children in the United States had elevated blood lead levels between 1991 and 1994.1 For most of these children, the lead source is in the home environment, often from household dust contaminated by deteriorating leaded house paint. Interior house paints containing lead were widely used before and during the 1940s.2 The use of lead in paint was greatly curtailed in the 1950s, and lead was banned as a paint additive in 1978.2 Despite this phase-out, leaded paint is found in the majority of residential buildings built before 1980.3Other lead sources in a child's environment may include dust and soil contaminated by vehicle exhaust (lead was used as a gasoline additive until 1996), lead introduced into the home from parents' work exposures or hobbies, lead in ceramics used to cook and store food, and lead in some ethnic folk medicines and cosmetics.4 Major risk factors for elevated blood lead levels reflect these sources and include residence in older homes, low family income, minority race, and residence in larger urban areas.1,5,6
The Centers for Disease Control and Prevention (CDC) periodically updates its recommendations for testing children for lead exposure to reflect the current state of knowledge regarding lead's health effects and the prevalence of lead exposure. Before 1991, CDC recommended that at-risk children be screened and given follow-up attention if their blood lead levels were ≥25 μg/dL.7 In 1991, CDC recommended that virtually all children 1 to 5 years of age be screened, and the level of concern was lowered to 10 μg/dL.4 Most recently, CDC recommended that screening efforts be targeted to high-risk neighborhoods and children, because the decreasing prevalence of elevated blood lead levels has made universal screening throughout the United States unnecessary.8 The American Academy of Pediatrics has concurred with these recommendations.9,10
Limited information is available on the extent to which at-risk children receive lead testing in accordance with CDC guidelines. This analysis was undertaken to determine the frequency of lead screening between 1988 and 1994 and the extent to which screening was performed in accordance with major risk factors for elevated blood lead levels among a nationally representative sample of children 1 to 5 years of age.
Data on children's history of blood lead testing and on their current blood lead levels were obtained from the Third National Health and Nutrition Examination Survey (NHANES III). The NHANES is an ongoing series of national studies of the health and nutritional status of the civilian noninstitutionalized population. NHANES III was conducted in 2 phases: phase 1 ran from October 1988 through September 1991 and phase 2 ran from October 1991 through September 1994. A detailed description of the sample design has been published elsewhere.11Briefly, sampling was based on a stratified multistage probability cluster design, with oversampling of blacks, Mexican-Americans, children 2 months to 5 years of age, and people ≥60 years of age to increase the reliability of estimates for these groups. A household interview was conducted in the home for each survey participant, followed by a separately scheduled physical examination at a mobile examination center. Only data for children 1 to 5 years of age were included in this analysis.
During the physical examination, ethylenediaminetetraacetic acid-anticoagulated whole blood was collected by venipuncture from examinees ≥1 year of age. Specimens analyzed for lead remained frozen at −20°C until analyzed. Blood lead levels were measured on a Perkin-Elmer model 5000 or 5100 graphite furnace atomic absorption spectrophotometer (Perkin-Elmer, Norwalk, CT), using the method of Miller et al.12 The graphite furnace atomic absorption spectrophotometer method included deuterium or Zeeman background correction and had a limit of detection of 1.0 μg/dL. The blood lead measurements were calibrated using standards prepared from lead nitrate Standard Reference Material 928 obtained from the National Institute of Standards and Technology (Gaithersburg, MD). Blood lead levels were measured in duplicate, and the mean of the results was used in this analysis. Blood lead levels ≥10.0 μg/dL were considered elevated in accordance with CDC guidelines.4
Hemoglobin was measured as part of a complete blood count on a Coulter S-PLUS JR quantitative, automated hematology analyzer (Coulter, Inc, Hialeah, FL) by a cyanmethemoglobin assay using fresh blood.13 Hemoglobin was measured in duplicate, with the mean value reported. The S-PLUS JR was calibrated directly with Coulter each morning, using S-CAL calibrators and 5-C quality control materials. In this analysis, anemia was defined as a hemoglobin level below CDC-recommended age-specific cutoff values.14
One adult individual from each household responded to the household interview. The respondent was the head of household (defined as the person owning or renting the home) or the spouse of the head of the household for 96% of children 1 to 5 years of age. This individual provided information about the household and the child's health history. History of lead testing was assessed by the question: “Was [child's name] ever tested for lead poisoning?” The variables included time of the survey, demographic characteristics, and factors related to the age and location of the family home, health insurance, and use of medical services, anemia and general health status, and characteristics of the child's mother and head of household (Table 1).
For the questions regarding health insurance coverage, there were multiple versions of the questionnaire, which differed with respect to the time frame referenced. Approximately one half of the respondents were asked about their Medicaid and private insurance coverage within the previous month, and one half were asked about their Medicaid coverage within the previous year and about their current private insurance coverage. Because information about Medicaid coverage within the previous year was missing for 61% of eligible children 1 to 5 years of age, it was assumed for this analysis that those who had current private insurance but were missing information on Medicaid did not have Medicaid coverage. Information about Medicaid coverage within the previous month was missing for <1% of eligible children 1 to 5 years of age.
The relationship between each of these characteristics and the likelihood of an elevated blood lead level, as well as history of blood lead testing, was assessed while controlling for the others using multiple logistic regression. Model selection via backward elimination was used to identify independent correlates significant at α = .05, based on t tests. After the initial model was defined, potential predictor variables that had been eliminated during the model selection procedure were individually tested for reintroduction into the model; any variables that achieved statistical significance on reentry were retained in the models.
Data from phases 1 and 2 of NHANES III are correlated to an unquantified degree because of the method used for allocating primary sampling units to each survey phase.15 The assessment of survey phase as a covariate in the regression models was, therefore, conservative, because the correlation between phases was ignored (J. Eltinge, personal communication, 1998).
The number of children with elevated blood lead levels who did not have a history of blood lead screening was estimated for phase 2 of the survey, broken down by selected characteristics predictive of blood lead level. These numbers were benchmarked to the March 1993 Current Population Survey population estimate for the United States because this date represented the approximate midpoint of phase 2 sampling.
All statistical analyses were performed using SAS and SUDAAN software with appropriate weighting and accounting for the complex sample design of the survey.15–17
Among individuals selected for study in NHANES III, the household interview response rate was 94% for participants 1 to 2 years of age and 91% for those 3 to 5 years of age. The physical examination was completed by 87% of selected participants 1 to 2 years of age and 85% of those 3 to 5 years of age.15 There were 5787 NHANES III participants between the ages of 1 and 5 years (12.0–71.9 months). Of these, 4624 (79% of the weighted sample) received a blood lead test, and 5677 (98% of the weighted sample) had a valid response to the interview item regarding a previous blood lead test. Correlates of failing to receive a blood lead test during NHANES III were evaluated in a multivariate regression model; not receiving a blood lead test was more frequent (P < .05) among those who were sampled during phase 1 of the survey (28% vs 15%), those who were 1 to 2 years of age (25% vs 19%), those in households with incomes at or above $20 000 per year (24% vs 18%), those who resided in the Northeast region of the United States (27% vs 18%–21% for the other regions), those who were sampled in seasons other than the spring (21%–24% vs 17%), and those who were not anemic (23% vs 1%).
Overall, 6.3% of children 1 to 5 years of age had elevated blood lead levels, and 10.2% had reports of previous blood lead testing. Of those with elevated blood lead levels, 33% had a previous blood lead test reported. Between phase 1 and phase 2 of the survey, the prevalence of elevated blood lead levels dropped nonsignificantly (P= .06) from 8.6% to 4.4%; the percentage reporting previous testing increased nonsignificantly (P = .49) from 8.9% to 11.5%; and the percentage of those with elevated blood lead levels who had previous testing increased nonsignificantly (P = .44) from 30% to 37%.
Table 2 shows independent risk factors for an elevated blood lead level during NHANES III, and Table 3 shows independent correlates of previous blood lead testing based on the multivariate logistic regression models. Being of minority race/ethnicity, living in an older home, residing in the Northeast or Midwest regions of the United States, being on Medicaid, having a head of household with <12 years of education, and having a history of anemia were significant factors in both models. Additional independent risk factors for an elevated blood lead level included being sampled in phase 1 of the survey, being 1 to 2 years of age, not having a regular doctor, and being sampled during the summer months. Additional independent correlates of a previous blood lead test included having moved less than twice in one's lifetime, having a female head of household, and having parents whose home language was English.
Table 4 shows the estimated number of children 1 to 5 years of age with elevated blood lead levels in 1993 (at the midpoint of phase 2) and the number of these children who did not receive blood lead screening by selected risk factors. Of an estimated 890 000 children with elevated blood lead levels, 60% were receiving Medicaid, 37% lived in homes built before 1946, and 43% were black, non-Hispanic. Among those who were receiving Medicaid, 29% lived in homes built before 1946 and 56% were black, non-Hispanic (data not shown). Among those who were not receiving Medicaid, 49% lived in homes built before 1946 and 24% were black, non-Hispanic. Of the estimated 564 000 children 1 to 5 years of age who had elevated blood lead levels and no previous screening test in 1993, 62% were receiving Medicaid, 40% lived in homes built before 1946, and 34% were black, non-Hispanic (Table 4).
This analysis indicated that ∼10% of US children 1 to 5 years of age had received blood lead testing before their participation in NHANES III in 1988–1994. Presumably, virtually all of these tests were screens or follow-ups of screens among asymptomatic children, because symptomatic lead poisoning is rare in the United States. This result is a lower estimate than that found in a 1994 national survey in which 24% of parents interviewed reported that their children had undergone lead screening tests.18 Two factors may have contributed to this discrepancy. One is that screening rates may have risen over the 1988–1994 period in response to the universal screening recommendations issued by CDC in 1991 and by the American Academy of Pediatrics in 1993.4,9 If this is the case, then the response to the recommendations was greater in later years, because the NHANES III data did not show a significantly higher screening rate in phase 2 (1991–1994) than in phase 1 (1988–1991). Unfortunately, it was not possible to analyze the NHANES data by year of interview to assess whether this was the case.
A second possibility is that the estimates were affected by selective nonparticipation in one or both surveys. The response rate for the 1994 telephone survey was 56%, compared with over 90% for NHANES III.15,18 It is possible that parents who chose to participate in the 1994 survey were more likely than nonparticipants to have children who were screened for lead or more likely to remember previous blood lead testing of their children.
Blood lead screening is generally conducted in a pediatrician's office as part of a routine, well-child visit. Because blood may be drawn at these visits for routine laboratory analyses and anemia testing as well as for lead testing, parents may not always be aware that a lead test is being performed. Thus, the estimates of testing prevalence found in this study, as well as in the 1994 telephone survey, may have been biased downward. However, a review of Medicaid claims records for 1994–1995 indicated a screening rate similar to that reported in NHANES III.19
The estimated prevalence of elevated blood lead levels may also be slightly inaccurate because blood lead data were missing for 21% of NHANES III participants 1 to 5 years of age. The primary reason for missing data was parental refusal of the blood draw.15Data were more likely to be missing for children living in the Northeast region of the United States and for younger children, both of whom tend to have higher blood lead levels, and for phase 1 recipients, who were sampled when blood lead levels were higher. Thus, the prevalence estimate may have been biased downward. However, data were also more likely to be missing for children who were sampled in the fall and winter months, for those who were not anemic, and for those who had an annual household income ≥$20 000. Blood lead levels were lower in the winter and spring, and both anemia and lower income were significantly associated with elevated blood lead levels on the bivariate analyses. Thus, the overall direction or degree of any bias is unclear.
Correlates of an elevated blood lead level in this analysis included being 1 to 2 years of age, being of minority race/ethnicity, having a lower income, and living in an older home, all of which are well-known risk factors whose relationships to elevated blood lead levels have been demonstrated in previous analyses of NHANES III data.1,5,6 Living in the Northeast was also shown to be a risk factor in a previous NHANES III analysis.5 Season did not predict continuously modeled blood lead concentrations in children in another NHANES III analysis but has been shown to predict blood lead levels elsewhere.6,20 Note that because NHANES III physical examinations were generally conducted in the northern United States during the warmer months and in the southern United States during the cooler months, the increased risk associated with residence in the Northeast and Midwest regions of the United States might be overestimated if the categorical coding for season incompletely controlled for the NHANES III examination schedule.
Being on Medicaid, not having a regular doctor, living in a household whose head has less than a high school education, and having a history of anemia were also independent risk factors in this analysis but were not evaluated in the previous NHANES III studies. Anemia has previously been shown to be correlated with elevated blood lead levels.21 Being on Medicaid is a close correlate of poverty, another well-known risk factor for lead exposure that probably reflects the condition of the child's home. Heads of household with less education may be less aware of lead hazards and, therefore, less able to protect their children, or lower education may be a proxy marker of lower socioeconomic status and poorer housing. Similarly, having a regular doctor may be a proxy for higher socioeconomic status or a more orderly lifestyle in which children are less likely to be exposed to lead hazards.
Of the correlates of blood lead testing, many were also risk factors for elevated blood lead levels in this analysis (being of minority race/ethnicity, living in an older home, living in the Northeast or Midwest regions of the United States, being on Medicaid, having a head of household with less than a high school education, and having a history of anemia). Of the remaining correlates of previous blood lead testing in this analysis, having a female head of household has been shown to be related to the likelihood of elevated blood lead levels in other studies.22 Increased residential mobility has also been shown to be a risk factor for elevated blood lead levels,23 but in this analysis a greater number of moves was associated with a decreased likelihood of being screened for lead exposure. Children with parents who spoke a language other than English at home were less likely to have received blood lead testing, perhaps reflecting less access to health care among these families.
In summary, these findings indicate that children with known risk factors for elevated blood lead levels were more frequently screened. However, among children with elevated blood lead levels, only one third had been tested previously. Clearly, many practitioners did not heed CDC's 1991 call for universal screening. Several surveys of pediatricians were conducted in the early 1990s to determine screening practices. The proportion of respondents reporting that they universally screen patients ranged from 12% to 75%, with higher proportions found in later years.24–27 The proportion reporting that they never screened patients ranged from 4% to 25%, and the proportion that screened selected patients ranged from 21% to 63%. These studies indicate that universal screening was more commonly practiced by pediatricians with more recent training, those who practiced in academic or public clinic settings, those who had a greater proportion of minority or Medicaid patients, those who believed the benefits of screening outweigh the costs, and those who reported a high prevalence of elevated blood lead levels among their patients.24–26 Among selective screeners, indicators for screening were generally in adherence with the 1991 guidelines of the CDC and included such factors as living in or regularly visiting an older home, having a history of pica, being enrolled in Medicaid, having a parent who uses lead for work or for a hobby, and having a sibling with an elevated blood lead level.4,24,25
Childhood lead poisoning prevention programs that are attempting to devise plans for reaching high-risk children should focus on those risk factors that can identify the greatest numbers of such children and can be assessed easily by pediatric practitioners. The candidate risk factors evaluated in terms of absolute numbers of high-risk children identified in this analysis were Medicaid status, race/ethnicity, and year the home was built. (Region of the country was not evaluated despite being a strong risk factor because of the possible bias introduced into the estimate by the survey design.) Among the factors evaluated, Medicaid status identified the greatest number of high-risk children by far. Although Medicaid-eligible children represented 30% of the NHANES III, phase 2 sample, they represented 60% of the population with elevated blood lead levels (535 000/890 000) and 93% of the population with blood lead levels ≥20 μg/dL (68 000/73 000; data not shown), the level at which children require clinical management.8 In addition, since 1992 the Health Care Financing Administration has required that all children receiving Medicaid benefits be tested for lead exposure.28 However, among NHANES III, phase 2 (1991–1994) Medicaid-eligible participants 1 to 5 years of age, 81% did not receive blood lead screening.29 Nonacceptance of federal screening policies and lack of oversight within state Medicaid programs have been identified as 2 reasons why many Medicaid-eligible children do not receive screening.19
Among the 355 000 NHANES III, phase 2 children with elevated blood lead levels who were not Medicaid-eligible, 49% (175 000) lived in homes built before 1946 and 24% (85 000) were black, non-Hispanic. Thus, focusing on the age of the child's home may be more useful than focusing on the child's race for identifying at-risk children among those who are not Medicaid-eligible. Year of housing construction has been also recommended as a factor on which health departments should base screening recommendations for neighborhoods.8 In addition, physicians can ask parents about the child's home during individual examinations. Not all parents know when their home was built (8% of respondents in this analysis did not know); the conservative approach for physicians would be to screen all such children.
The ideal approach to childhood lead poisoning is primary prevention by removing exposure sources, and, in fact, the prevalence of elevated blood lead levels among children 1 to 5 years of age has dropped 95% since the late 1970s because of the removal of lead from gasoline, food and drink cans, house paint, and plumbing.1,6,30 However, remaining lead sources, such as deteriorating house paint, must be addressed on an individual, rather than on a population, level. Therefore, secondary prevention through screening to identify exposed children, followed by environmental remediation and treatment, remains important. Physicians should screen Medicaid-eligible children and should follow health department recommendations about identifying and screening other at-risk children. In areas where no health department guidelines exist, physicians should either screen all children or screen based on known risk factors.
- Received October 19, 1999.
- Accepted July 24, 2000.
Reprint requests to (R.B.K.) E-25, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA 30333. E-mail:
- CDC =
- Centers for Disease Control and Prevention •
- NHANES III =
- Third National Health and Nutrition Examination Survey
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- Centers for Disease Control and Prevention. Preventing Lead Poisoning in Young Children: A Statement by the Centers for Disease Control. Atlanta, GA: US Department of Health and Human Services, Public Health Service; 1991
- Centers for Disease Control and Prevention. Preventing Lead Poisoning in Young Children: A Statement by the Centers for Disease Control. Atlanta, GA: US Department of Health and Human Services, Public Health Service; 1985
- Centers for Disease Control and Prevention. Screening Young Children for Lead Poisoning: Guidance for State and Local Public Health Officials. Atlanta, GA: US Department of Health and Human Services, Public Health Service; 1997
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- Centers for Disease Control and Prevention. Plan and operation of the third National Health and Nutrition Examination Survey, 1988–1994. Vital Health Stat 1. 1994;32
- Gunter EW, Lewis BG, Koncikowski SM. Laboratory Procedures Used for the Third National Health and Nutrition Examination Survey (NHANES III), 1988–1994. Atlanta, GA: Centers for Disease Control and Prevention; 1996
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- Centers for Disease Control and Prevention. Analytic and Reporting Guidelines: The Third National Health and Nutrition Examination Survey, NHANES III (1988–1994). Hyattsville, MD: National Center for Health Statistics; 1996
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- Shah BV, Barnwell BG, Bieler GS. SUDAAN User's Manual, Release 7.5. Research Triangle Park, NC: Research Triangle Institute; 1997
- US General Accounting Office. Lead Poisoning: Federal Health Programs Are Not Effectively Reaching At-Risk Children. Washington, DC: US General Accounting Office; 1999. GAO/HEHS-99-18
- US Environmental Protection Agency. Seasonal Rhythms of Blood-Lead Levels: Boston, 1979–1983. Washington, DC: Office of Prevention, Pesticides, and Toxic Substances; 1995. EPA 747-R-94-003
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- Health Care Financing Administration. State Medicaid Manual. Health Care Financing Administration; 1992. 5123.2:45–5
- US General Accounting Office. Medicaid: Elevated Blood Lead Levels in Children. Washington, DC: Health, Education, and Human Services Division; 1998. GAO/HEHS-98-78
- US General Accounting Office. Children's Health: Elevated Blood Lead Levels in Medicaid and Hispanic Children. Washington, DC: Health, Education, and Human Services Division; 1998. GAO/HEHS-98-169R
- Copyright © 2000 American Academy of Pediatrics