Lead Screening and Prevalence of Blood Lead Levels in Children Aged 1–2 Years — Child Blood Lead Surveillance System, United States, 2002–2010 and National Health and Nutrition Examination Survey, United States, 1999–2010

Jaime Raymond, MPH1

Will Wheeler, MPH2

Mary Jean Brown, ScD1

1Division of Emergency and Environmental Health Services, National Center for Environmental Health, CDC

2Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion, CDC

Corresponding author: Jaime Raymond, Division of Emergency and Environmental Health Services, National Center for Environmental Health, CDC. Telephone: 770-488-3627; E-mail: zvu0@cdc.gov.

Introduction

Lead poisoning in children is preventable. However, in 2010, a total of 34 U.S. states and the District of Columbia (DC) identified approximately 24,000 children aged <6 years with blood lead levels (BLLs) ≥10 µg/dL and approximately 243,000 children aged <6 years with BLLs ≥5 µg/dL, the upper reference range value* established in 2012 for follow-up blood lead testing in children aged 0–6 years (1). Permanent neurologic damage and behavior disorders have been associated with lead exposure even at detectable BLLs <5 µg/dL (2–5).

In 1991, CDC recommended that identification of children with BLLs ≥10 µg/dL should prompt public health action by state or local health departments with follow-up testing (6). In 2012, CDC's Advisory Committee for Childhood Lead Poisoning Prevention (ACCLPP) recommended that CDC shift its priorities to primary prevention. ACCLPP provided additional guidance to clinicians related to the follow-up of children with BLLs of 5–10 µg/dL on the basis of evidence that these levels are associated with IQ deficits, attention-related behaviors, and poor academic achievement (7–10). ACCLPP also recommended using a reference range value based on the estimated 97.5 percentile of the BLL distribution among children aged 1–5 years calculated from two 4-year cycles of National Health and Nutrition Examination Survey (NHANES) data. In 2010, the upper value of the reference range was 5 µg/dL.

The Bright Futures guidelines, adopted by the American Academy of Pediatrics (AAP) in 1998 and endorsed by the Health Resources and Services Administration (HRSA) recommend that a clinical risk assessment for lead exposure be performed for infants (at ages 6 and 9 months), with blood lead testing to follow if positive. The assessment includes questions about Medicaid eligibility and living in housing built before 1978. The Bright Futures guidelines also recommend that children who are enrolled in Medicaid or living in high-risk areas as defined by the state or local health departments be screened for lead at ages 12 and 24 months (11). The National Committee for Quality Assurance has established a specific Healthcare Effectiveness Data and Information Set measure (i.e., the percentage of children who had one or more capillary or venous blood test for lead poisoning by their second birthday) (12). Because lead risk varies across the United States, the most recent CDC lead screening recommendations urge state and local health departments to assess local data on lead risks as the basis for developing lead screening recommendations for health-care providers that target children at risk in their areas, focusing on children aged 1–2 years (13).

Several risk factors are associated with lead exposure. The most common risk factor is living in a housing unit built before 1978, the year when residential use of lead paint was banned in the United States. If a child is identified as having a BLL ≥5 µg/dL, ACCLPP recommends further assessment of the child and the home environment, follow-up treatment, and retesting the child's BLL until it has decreased to either <5 µg/dL or <10 µg/dL, depending on the state's guidelines (7). Follow-up treatment will vary depending on the child's BLL but might include health education, environmental investigations of the home or other places the child frequents, and chelation therapy (13). Data from state and local blood lead surveillance programs also can guide targeted primary prevention activities that control or eliminate lead sources before children are exposed and highlight geographic areas and special subpopulations (e.g., refugee populations) for which the risk for lead poisoning is greatest. A Healthy People 2020 objective (objective EH-8.2) is to reduce the mean BLLs in children aged <6 years by 10% (14). The baseline level is 1.5 µg/dL, and the goal is 1.4 µg/dL. Another Healthy People 2020 objective (objective EH-8.1) is to eliminate BLLs ≥10 µg/dL in the same population (14).

The reports in this supplement provide the public and stakeholders responsible for infant, child, and adolescent health (including public health practitioners, parents or guardians and their employers, health plans, health professionals, schools, child care facilities, community groups, and voluntary associations) with easily understood and transparent information about the use of selected clinical preventive services that can improve the health of infants, children, and adolescents. The topic in this report is one of 11 topics selected on the basis of existing evidence-based clinical practice recommendations or guidelines for the preventive services and availability of data system(s) for monitoring (15). This report analyzes 2002–2010 data from CDC's Child Blood Lead Surveillance (CBLS) System to determine the proportion of U.S. children aged 1–2 years who were tested for lead. State and local health departments have their own definitions of the criteria for identifying children who are at risk, with a focus on children aged 1–2 years. However, because a single national definition of children at risk does not exist, establishing the screening rate of children at risk is not possible. This report also analyzes 1999–2010 data from NHANES to examine prevalence of BLLs ≥5 µg/dL and ≥10 µg/dL among children aged 1–2 years over time by factors that historically have predicted the risk for BLLs at or above the current reference value. Public health authorities and clinicians can use these data to identify population subgroups with suboptimal screening rates and target prevention tactics.

Methods

To estimate the proportion of children aged 1–2 years who were tested for lead, CDC analyzed 2002–2010 data from CBLS, and to calculate the prevalence of BLLs ≥5 µg/dL and ≥10 µg/dL among children aged 1–2 years, CDC analyzed data from three 4-year intervals of NHANES (1999–2002, 2003–2006, and 2007–2010). Using 4-year intervals provided a greater number of children tested and yielded more stable estimates. CDC recommends that state and local departments should identify children at high risk for BLLs ≥5 µg/dL and provide access to screening for lead, focusing on children aged 1–2 years (8). Regardless of whether they were obtained from children at high risk, all qualified blood lead tests (defined as having certain information for completeness [i.e., date of birth, blood lead level, and date of blood lead test]) are reported to CBLS. During 2002–2010, the number of state and local health departments reporting BLLs to CBLS ranged from 36 to 44. Annual screening rates were calculated by dividing the number of children aged 1–2 years with a valid blood test in CBLS for each reported year by the U.S. Census estimates of the number of children aged 1–2 years during each year that jurisdictions submitted data to CBLS. Every effort was made to count children with multiple tests only once.

State and local childhood lead surveillance systems are passive surveillance systems that rely on BLL test results reported by private and public laboratories. Reporting criteria are set by each state and vary across jurisdictions, although by 2002, a total of 29 states mandated reporting of all BLLs (16). Test results are compiled and put through quality assurance measures by state health departments. The results are submitted quarterly to CDC and entered into CBLS. Because of missing information, demographic data, including race/ethnicity, Medicaid status, and housing status were not used for this analysis.

This report provides CBLS data for children aged 1–2 years who were tested for BLLs at least once during January 1, 2002–December 31, 2010. The following are surveillance definitions for all states:

• Test: Any blood lead drawn (capillary, venous, or unknown sample type) on a child that produces a quantifiable result and is analyzed by a Clinical Laboratory Improvement Amendments (CLIA)–certified facility or an approved portable device. A blood lead test may be collected for screening, confirmation, or follow-up.
• Confirmed BLL ≥10 µg/dL: A child with one venous blood specimen ≥10 µg/dL, or two capillary blood specimens ≥10 µg/dL drawn within 12 weeks of each other (2,3).
• Unconfirmed BLL ≥10 µg/dL: A single capillary blood lead test ≥10 µg/dL, or two capillary tests ≥10 µg/dL with >12 weeks apart.
• BLL 5–9 µg/dL: A single blood lead test (capillary or venous) with a result of 5–9 µg/dL.

To estimate the national prevalence of BLLs ≥5 µg/dL and ≥10 µg/dL among children aged 1–2 years, CDC used data from NHANES, a cross-sectional, nationally representative survey of the noninstitutionalized U.S. population. Since 1999, NHANES has been conducted as an ongoing survey, with data reported in 2-year cycles. NHANES survey and analytic methods have been described previously (17). The analyses provided in this report are made on the basis of NHANES data on children aged 1–2 years who were tested. Through the NHANES analyses, CDC has defined a BLL ≥5 µg/dL as high. The percentage of children living in older housing with BLLs ≥5 µg/dL as well as demographic characteristics and 95% confidence intervals also were calculated. Statistically significant differences in demographic characteristics and housing were evaluated using pairwise t-tests, and differences were considered statistically significant at p<0.05. This report includes the available data from 1999–2010. To assess the prevalence of BLLs ≥5 µg/dL over time among children aged 1–2 years living in housing built before 1950, housing built during 1950–1977, and housing built after 1977, CDC analyzed data from the six most recent NHANES cycles (1999–2000, 2001–2002, 2003–2004, 2005–2006, 2007–2008 and 2009–2010). For some of the NHANES analyses, the estimates are not reliable (i.e., relative standard error is ≥30) but are the best that are available for the U.S. population, and the sample sizes are small across variables only for the age group 1–2 years.

Prevalence rates in the NHANES data with BLLs ≥5 µg/dL were analyzed by sex, race/ethnicity, poverty-to-income ratio, Medicaid status, and age of housing. Statistical analyses were performed using SAS version 9.2 (18) and SUDAAN 10.0.1 (19), a software package that incorporates the sample weights and adjusts the analyses for the complex sample design of NHANES. All analyses used examination sample weights to account for the unequal probability of election, oversampling, and survey nonresponse.

Results

In 2002, CBLS received reported BLLs from 43 states and DC; BLL tests were reported for approximately 22% of children aged 1–2 years (Table 1). By 2010, the BLL screening rate for this age group had increased to 33.4%. The number of children aged 1–2 years screened for BLLs reported to CDC ranged from 1,617,667 (982,005 children aged 1 year and 635,662 children aged 2 years) in 2002 to a high for the study period of 2,557,445 (1,506,620 children aged 1 year and 1,050,825 in children aged 2 years) in 2009. In 2010, a total of 2.0% of children aged 1–2 years tested had confirmed BLLs ≥10 µg/dL compared with 9.3% in 2002. The percentage of children aged 1–2 years tested with BLLs 5–9 µg/dL also decreased from 14.9% in 2002 to 4.2% in 2010.

NHANES data from 2007–2010 indicate that 3.1% of children aged 1–2 years had BLLs ≥5 µg/dL. Among non-Hispanic black children aged 1–2 years, 7.7% had BLLs ≥5 µg/dL compared with 1.6% of Mexican-American children aged 1–2 years (95% CI = 0.7–3.0). Differences for the prevalence of BLLs ≥5 µg/dL were observed by poverty levels; 6.0% of children living in a household with a poverty-to-income ratio of <1.3 had BLLs ≥5 µg/dL, compared with 0.5% of children living in a household with a poverty-to-income ratio of ≥1.3 had BLLs ≥5 µg/dL. These findings indicate the same disparity in risk by factors that have been important historically (Table 2).

The NHANES estimate of the percentage of children aged 1–2 years living in pre-1950 housing remained steady from 1999 to 2010 (Table 3). The greatest decline in the percentage of children having BLLs ≥5 µg/dL from 1999 to 2010 occurred among children living in pre-1950 housing (25.9% versus 3.7%, respectively; p<0.05) (Table 3). However, children living in pre-1950 housing were 10 and four times more likely to have BLLs ≥5 µg/dL compared with children living in homes built after 1978 during the NHANES 1999–2002 and 2007–2010 cycles, respectively (Table 3).

Discussion

During 2002–2010, lead screening rates in children aged 1–2 years increased from 21.5% in 2002 to 33.4% in 2010. Because of the limitation of the demographic data in CBLS and the lack of a single national definition of children at risk, the screening rate of children at risk cannot be established. In 2008, a total of 24,546 children aged 1–2 years had confirmed BLLs ≥10 µg/dL, compared with 19,915 children with such levels in 2010. Taken together, CBLS and NHANES data indicate that the Healthy People 2010 objective of eliminating BLLs ≥10 µg/dL has not been achieved. An analysis conducted by the Centers for Medicare and Medicaid Services indicated that approximately 66% of children enrolled in Medicaid were screened for lead during 2008–2009 despite the requirement that all children enrolled in Medicaid receive a blood lead test at ages 12 and 24 months (20).

The reduction in disparities by housing and demographic factors might indicate success in screening and interventions for the children at highest risk. However, the persistence of these disparities also underscores the need to continue efforts to ensure identification of children with BLLs at or above the reference range value.

According to the U.S. Preventive Services Task Force (USPSTF), blood lead screening for children is a Grade I recommendation, which means that the evidence is insufficient to recommend for or against routine screening for elevated blood lead levels in asymptomatic children aged 1–5 years who are at increased risk (21). Nonetheless, as this report indicates, children who are on Medicaid, living in poverty, and living in older housing are more likely than other children to have BLLS ≥5 µg/dL. For this reason, the screening rate for these children needs to be improved. Because the majority of children with BLLSs ≥5 µg/dL are asymptomatic, children who are at risk for lead exposure need to be tested to determine if their exposure is high. Subsequently, lead hazards in their environments need to be addressed to reduce permanent neurologic disorders directly resulting from BLLs ≥5 µg/dL. The key stakeholders for improving lead screening include CDC, state and local health departments, and primary care providers. It is essential that state and local health departments improve their communications to primary care providers in the areas and populations of children within their state and locality at high risk for lead exposure. CDC concurred with ACCLPP's recommendation for education and follow-up testing for children with BLL's ≥5 µg/dL; this is accomplished typically through a letter from the health department to the primary care provider, but more opportunities exist to improve screening children at high risk, such as Geographic Information Systems mapping to show providers the high-risk areas (22). Primary care providers can use and disseminate this information from state and local health agencies. Increasing primary care providers' knowledge of lead exposure will make it more likely that they will screen children at high risk in their area. Also, it is important that all parents receive education on how to prevent lead exposure in the home and that children at high risk be screened for lead.

Previous cost effectiveness studies of lead screening indicate that universal screening is the most cost-effective strategy in high-prevalence populations (23). In the late 1990s, the cost per confirmed BLL ≥10 µg/dL in a high-prevalence neighborhood population was $490. The cost of a blood lead test ranges from $10 to $75 (23). As a result of the 2012 change in reference value to 5 µg/dL, studies are needed to evaluate the cost-effectiveness of screening children for lead at this level. In addition, further research would support opportunities to evaluate what strategies would be effective in further increasing screening rates in young children.

An estimated $43 billion in annual costs for medical care and potential productivity losses of affected children when they become adults are attributed to lead as an environmental pollutant (24). Since 1991, federal and state agencies have adopted requirements for lead-safe work practices and developed a trained and visible workforce that can safely eliminate lead paint hazards in housing, implemented stricter standards for lead in products marketed to children and reduced lead concentrations in water (25). State and local health and housing programs have used local data to identify geographic areas and subpopulations at high risk for BLLs ≥5 µg/dL and ≥10 µg/dL, as well as specific properties on which many children have been exposed to the same lead hazards over time. Each state has used its data to determine where the high-risk areas lie and developed targeted screening plans. For example, Ohio has mapped confirmed BLLs ≥10 µg/dL by county to show providers high-risk areas (26). These data should be used to continue to direct lead paint hazard control resources, identify new sources of lead exposure (e.g., traditional pottery or medicines in newly arrived populations), and anticipate increased lead exposure resulting from environmental changes (e.g., alterations in water chemistry that might increase lead solubility in water). CDC's Lead Poisoning Prevention Program will continue to research better ways to target screening children at high risk in the United States and to analyze trends in lead exposure in children through data from state and local health departments across the United States. The U.S. Department of Housing and Urban Development could use CDC's prevalence data to provide strategies to identify those areas to which healthy housing funds should be distributed (i.e., the areas at highest risk). Efforts are needed for nonprofit organizations to continue to promote programs and policies that are in line with the screening guidelines and for health and housing departments to pursue efforts to increase screening among children living in high-risk housing.

Ongoing changes in the U.S. health-care system offer opportunities to improve the use of clinical preventive services among infants, children, and adolescents. The Patient Protection and Affordable Care Act of 2010 (as amended by the Health Care and Education Reconciliation Act of 2010 and referred to collectively as the Affordable Care Act [ACA]) expands insurance coverage, consumer protections, and access to care and places a greater emphasis on prevention (27). As of September 23, 2010, ACA § 1001 requires nongrandfathered private health plans to cover, with no cost-sharing, a collection of four types of clinical preventive services, including 1) recommended services of USPSTF graded A (strongly recommended) or B (recommended) (28); 2) vaccinations recommended by the Advisory Committee on Immunization Practices (29); 3) services adopted for infants, children, and adolescents under the Bright Futures guidelines (30) and those developed by the Discretionary Advisory Committee on Heritable Disorders in Newborns and Children (31); and 4) women's preventive services as provided in comprehensive guidelines supported by HRSA (32). The Bright Futures guidelines recommend lead screening for children at multiple points as a child ages on the basis of the risk for lead exposure (10). State Medicaid programs cover lead screening as part of the Early and Periodic Screening, Diagnostic and Treatment benefit.

The Health Insurance Marketplace (or Health Insurance Exchange) began providing access to private health insurance for small employers and to persons and families interested in exploring their options for coverage, with policies taking effect as early as January 2014.† Federal tax credits are available on a sliding scale to assist those living at 100%–400% of the federal poverty level (FPL) who purchase health insurance through the Marketplace (ACA § 1401). Insurance plans sold on the Marketplace must cover the four types of recommended clinical preventive services without cost-sharing, including lead screening.

Limitations

The findings in this report are subject to at least three limitations. First, approximately 4.3 million children are tested in 34 states and the District of Columbia, each jurisdiction collating its own data and conducting its own quality assurance measures. The information about the child and the blood lead test often is transferred from the clinical laboratory through various channels to the health-care provider and ultimately to the state health department. To assign one test per year to a child, state-based programs must match multiple tests for a child or risk having duplicate records per child in their systems. Second, CBLS does not collect children's names or street address information, requiring state health departments to de-duplicate child records using data available at the state level. As a result, children might not be matched correctly, and the data could be missing confirmed BLLs. Finally, blood lead estimates from CBLS and NHANES should be used to complement one another; the data should not be compared because each system has distinct methodologies and different data collection protocols. The state surveillance systems provide data at state and local levels that can be used to target screening efforts and primary prevention practices to children at high risk. However, because not all children at high risk are tested, CBLS does not provide a complete accounting of all children at high risk in a given jurisdiction. A study conducted in 2001 indicated that 61% of the children tested in a high-risk neighborhood had never had a blood lead test (33). Thus population prevalence values cannot be calculated by using CBLS data.

NHANES data represent a national representative sample, and estimates generated from the data are generalizable to the U.S. population as a whole. In addition, since NHANES was not designed to produce estimates at the state and local level, it might overlook statistically significant disparities that have important public health implications at state and local levels. NHANES also has a high proportion of missing data for age of housing. NHANES and state surveillance data also differ in methods of blood lead test samples. For NHANES, all blood lead tests are collected by venous sampling, the most accurate method and analyzed using inductively coupled plasma mass spectrometry at a single laboratory at CDC (17).

Blood lead tests reported to state and local health departments can be either a venous or a repeat capillary sample. Capillary samples are not as accurate as venous samples and are easily contaminated if proper procedures are not followed (34). However, capillary BLLs have been demonstrated to provide adequate estimates at the population level (34). CDC recommends that children with capillary tests with BLLs ≥10 µg/dL be retested with a venous sample or capillary sample within 12 weeks. However, this is not always possible, and thus CBLS might underestimate or overestimate the number of children with BLLs ≥10 µg/dL because children are lost to follow up before providing a confirmatory sample (35).

Conclusion

Screening and early identification of children at risk for lead exposure has the potential to prevent permanent neurologic damage and behavioral disorders in hundreds of thousands of young children across the United States. Increasing the number of children with regular access to primary care, environmental assessment, and lead hazard control could substantially reduce the number of young children in the United States with BLLs ≥5 µg/dL. CDC will continue to work closely with state and local health departments to find ways to increase blood lead screening for children at risk. These data have important uses beyond identification of children in need of services as they can be used to identify subpopulations and geographic areas where primary prevention activities can be used and reduce or eliminate lead sources before children are exposed.

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