The Shifting Landscape of Lead Exposure: Screening Gaps for Children in North Carolina.

Many children at risk of elevated blood lead level (EBLL) are never tested.[1,2] For example, an estimated 35%–60% of children enrolled in Medicaid are not screened,[3,4] despite the requirement that states provide lead testing for all such children.[5] A recent study in Environmental Health Perspectives[6] quantified screening gaps in North Carolina by linking more than 630,000 children born in the state between 2011 and 2016 to reported lead test results from 2011 to 2018.

Children’s blood lead levels (BLLs) declined substantially following the reduction or phaseout of historical exposure sources—namely, lead in drinking water and most leaded paints and fuels. This decline is considered a public health success in the United States and many other countries.[7] Still, EBLLs in children continue to be a worldwide health problem; about 815 million children globally may have a BLL above [8] (the former reference value set by the U.S. Centers for Disease Control and Prevention, which the agency lowered to in October 2021[9]).

Lead screening strategies may be undercut by assumptions about which children are and are not at high risk for EBLL. The authors estimated that, had all children born in North Carolina between 2011 and 2016 been tested by age 30 months, an additional 17,543 children with EBLLs would have been identified. Image: © Kadmy/adobe.stock.com.

The authors of the new study used the North Carolina birth cohort to derive demographic predictors of who will be tested for lead. They applied a statistical method to construct a hypothetical full cohort with complete BLL data and demographic features that matched the real cohort. They estimated that if all children born in North Carolina from 2011 to 2016 had been tested, an additional 17,543 children under 30 months of age would have been identified as having a BLL of or higher. (The cutoff was set at rather than due to rounding of reported numbers.)

The authors concluded that the current strategy of screening only those children assumed to be high risk may miss more than 30% of North Carolina children with EBLL. For first author Elizabeth Kamai, now a postdoctoral researcher at the University of Southern California, that number is disappointingly high. She notes, however, that more than 63.5% of children born in the state were tested between 2011 and 2018, of whom more than 10,000 exceeded the previous reference value of . That testing proportion is higher than earlier findings for North Carolina[10] and other states.[11]

The researchers combined the geocoded birth records with several environmental data sets to compare associations between EBLL and a broad range of individual- and neighborhood-level risk factors in both the tested subset and the hypothetical full cohort. Among these predictors were having Medicare coverage, use of private (typically untested) drinking water sources, proximity to a major roadway or lead-releasing industrial site, and residing in a neighborhood with homes built before 1940 or 1950. Kamai explains that, although lead risk is typically associated with housing built before 1978,[12] the team used 1940 and 1950 as cutoffs in keeping with extensive literature showing associations between housing built prior to these periods and EBLL.

“Our results show that historically significant exposure sources are becoming less important than other sources for low-level exposures, which do have adverse health effects,” says Kamai. For example, the authors reported that private drinking water sources or living near a major roadway, airport, or industrial lead emission source conferred a risk increase similar to that of living near old housing stock.

Lead continues to be used in some industries[13] and the fuel for single-piston aircraft.[14] In addition, because lead is extremely stable in the environment, pollution released decades ago may still contaminate soil and roadways.[15,16] The distribution of environmental hazards often tracks with neighborhood socioeconomic differences and contributes to persistent racial disparities in children’s EBLLs.[17,18]

Katarzyna Kordas, an associate professor of epidemiology and environmental health at the University at Buffalo, appreciates the authors’ novel strategy for quantifying both statewide screening gaps and the magnitude of selection bias in analyses that are restricted to tested children. “The results should motivate pediatricians and public health officials to increase testing because the assumptions behind current screening tools may not capture children’s actual exposure,” says Kordas, who was not involved in the study.

A perfect example, she adds, is that children in rural parts of North Carolina had a higher risk of EBLL than those in urban areas,[5,19] in contrast to common assumptions. “Some health care providers may assume that because their community is not demonstrating the typical risk factors, it is not affected by lead. But as this study shows, this could be far from the truth,” Kordas says.

Eri Saikawa, an associate professor of environmental sciences at Emory University, says multipronged efforts are needed to increase testing rates. “Enhanced provider training is important, but we should also address other barriers, such as parental concerns that blood draws may be painful for very young children,” says Saikawa, who was not involved in the study. Self-administered blood collection devices that are less painful than finger pricks and needles have already been used in research settings.[20,21]

Kordas and Saikawa support the authors’ call for universal lead testing, which has been implemented in Washington, DC, and 10 states.[22] Kamai underscores the need, saying, “Identifying and mitigating childhood lead exposure continues to be a population-level problem that requires policy changes and cannot be solved by individuals alone.”