Right now, according to public health officials, about half a million U.S. kids have blood lead levels that could harm their health. However, new research finds many more children — hundreds of thousands more — are likely going unidentified.

In a study published last week in Pediatrics, researchers estimated that while 1.2 million cases of elevated blood lead levels (EBLL) likely occurred between 1999 and 2010, only 607,000 were reported to the Centers for Disease Control and Prevention. That data gap not only means kids are likely going without needed treatment and services, but that public health officials don’t have all the data they need to ensure prevention and remediation efforts reach everyone who needs them. And if — as the study suggests — public health officials don’t have complete data on where lead poisoning threats exist, it makes it difficult to pinpoint the sources of exposure and prevent additional poisonings in the future.

According to CDC, there’s no safe blood lead level in children, and even low levels of lead have been shown to impact IQ, attention and academic achievement. Other effects of childhood lead poisoning include damage to the nervous system, slowed growth and development, behavioral issues, and hearing and speech problems. Research has found that investing in lead hazard control reaps significant benefits, both in preventing the high cost of special care and services and in protecting a child’s opportunity to succeed academically, which is often a predictor of future health, prosperity and longevity. In California alone, research shows that EBLL results in lost earnings of up to $11 billion over the lifetime of children born each year.

Study co-author Eric Roberts, a pediatrician and co-principal investigator of the California Environmental Health Tracking Program at the Public Health Institute, said that because the standards determining who should be tested for lead vary across states, he and colleagues had a hunch many at-risk and impacted children were being overlooked. According to the Pediatrics study, the American Academy of Pediatrics recommends clinicians refer to state and local lead screening guidelines, “but these recommendations are often difficult for clinicians to access and commonly defer to practitioners’ individual evaluations of EBLL risk in the communities they serve, a task for which few are equipped.” And while laws require lead testing for Medicaid and WIC enrollees, researchers said the requirement often goes unenforced. That means childhood lead testing is mostly left to the discretion of physicians.

“We did observe almost universally that when you ask state or local public health to quantify the amount of lead poisoning, they provide you with numbers of lead-exposed kids identified by physicians — and that always struck me as a circular argument,” Roberts told me. In other words, in communities where physicians do a lot of testing, the resulting data underscores the need to sustain and possibly expand such testing; if little testing is done, the resulting data can cause physicians to incorrectly believe testing isn’t necessary.

He added: “Right now, folks are just assuming that certain communities are at low risk. But the default should be for testing, especially for children 12 to 24 months old. …We now assume no risk until it’s found, and that policy is clearly failing to protect kids.”

To conduct the study, Roberts and colleagues used National Health and Nutrition Examination Survey (NHANES) data to estimate state-level EBLL prevalence among children ages 12 months to 5 years between 1999 and 2010. They then compared those estimates to diagnostic case numbers reported to CDC. They found that in 23 of the 39 states where data was available, more than half of children with EBLL weren’t being identified. Nationwide, according to the study, only 64 percent — or 607,000 cases — of children with EBLL were identified and reported to CDC.

Between 1999 and 2010, researchers estimated that about 1.2 million children had EBLL, but only those 607,000 cases were identified and reported to CDC. The researchers noted that about 45 percent of unreported cases happened in years when the particular state wasn’t reporting such data to CDC, and about 55 percent of unreported cases weren’t reported due to “incomplete case ascertainment.” At the regional level, the greatest number of reported EBLL cases occurred in the Midwest and Northeast, while the highest number of overall cases occurred in the South. At the state-level, 23 states reported fewer than half of expected EBLL cases, while 11 states reported less than 20 percent of expected cases. For example, in California, the study estimated that only 37 percent of children with EBLL were identified.

Researchers noted that because of changes to NHANES data collection in 2010, clinician testing has become the only source of information on EBLL prevalence. In addition, CDC’s Childhood Lead Poisoning and Healthy Homes Program had its budget cut in 2012 from $29 million to $2 million, which means states have much less capacity to do lead-related surveillance, outreach, education, prevention, assessment and enforcement.

Co-authors Roberts, Daniel Madrigal, Jhaqueline Valle, Galatea King and Linda Kite write:

American Academy of Pediatrics policy…explicitly defers to state and local health departments to decide when children should undergo BLL testing. This policy is based on two assumptions, however: that well-resourced public health agencies will communicate effectively with providers, enabling them to make data-directed decisions about when to test for EBLL, and that statutory requirements for testing would
 be accompanied by mechanisms 
and resources for enforcement. Both of these assumptions have proven to be false, with the effect 
that large numbers of children
 with EBLL (indeed, the majority 
of these children in many parts of
 the country) have been missed by clinicians.

“I think the fundamental message here for public health is that we need to realize that simply enumerating the number of kids found by pediatric care providers is not a scientific basis for knowing whether kids are at risk or not,” Roberts told me. “(Lead exposure) is a much wider-spread problem than we’ve been willing to admit.”

Roberts noted that while the most common route of child lead exposure is lead-based house paint — and that risk has been drastically reduced in recent decades — the drinking water crisis in Flint shows that lead remains a serious threat to children’s health. In fact, he said as aging infrastructures deteriorate, children could face new lead exposure risks, which is all the more reason for better surveillance, testing and data.

On the clinical side, he said groups like the American Academy of Pediatrics can make a difference by strengthening their practitioner guidelines for childhood lead testing, with the understanding that local public health data might not provide a complete picture of who’s at risk and who should be tested.

“What we’re doing when we allow kids to be exposed to lead is we’re sacrificing some portion of their futures,” Roberts said. “There’s a cost to doing nothing.”

For a copy of the new lead study, visit Pediatrics.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for 15 years. Follow me on Twitter — @kkrisberg.