Often when a child is poisoned by lead, there are no symptoms. Only a blood lead level test alerts parents to the danger. Otherwise, the child is at risk for irreversible learning disabilities and developmental delays. “By the time they see me when they’re school age, the lead is gone and has already done its damage,” said Jennifer Lowry, MD, a pediatrician at Children’s Mercy Hospital in Kansas City, Missouri, and director of the Mid-America Pediatric Environmental Health Specialty Unit. “I can’t do anything at that point.”
While a blood lead level test is simple to perform and inexpensive, an investigation by Reuters in June 2016 found millions of American children have not been tested, even when state laws or their health insurance plans require it. Children insured through Medicaid are required to have blood lead level tests at ages 1 and 2, yet in practice not all of these children are screened. Some states also require testing, but requirements vary.
The American Academy of Pediatrics recommends blood lead level testing only for children who are determined to be at risk for lead exposure or who live in high-prevalence areas. Likewise, the U.S. Centers for Disease Control and Prevention’s (CDC) 2012 recommendation discourages universal screening in favor of primary prevention. For example, it recommends doctors talk to all parents about proactively checking their homes for lead, rather than waiting to do so until lead has been found in their child’s blood.
Yet removing lead from a home is a daunting task, even once a child is discovered to have been poisoned. And sometimes parents aren’t even aware that lead may be coming into their homes. When Flint, Michigan, switched water sources in 2014 and lead seeped into drinking water from corroding pipes, children’s blood lead levels were the first evidence confirming widespread lead exposure.
Selecting the Best Method
The CDC maintains there is no safe amount of lead in a child’s blood. After years of lowering the threshold for action, its 2012 recommendation switched to a statistical calculation. The current actionable blood lead level is 5 µg/dL, based on the 97.5th percentile of U.S. children age 1 to 5 years.
Since the threshold was lowered, there has been an uptick in confirmatory testing at laboratories such as St. Louis Children’s Hospital, said Sarah Brown, PhD, medical director of a community lead screening program funded by the state of Missouri, and co-director of clinical laboratories at St. Louis Children’s. “Now basically anything that is positive on the screening device, we send off for confirmatory testing,” Brown said. “It increased our confirmatory testing volume by about 30 percent.”
The community nurses in Brown’s program use the Magellan Diagnostics Lead Care II point-of-care (POC) device when they visit Head Start programs and daycare centers in St. Louis. Though the device is CLIA-waived, the laboratory treats it as if it were not, training the nurses and putting them through competencies and College of American Pathologists proficiency testing, according to Brown. “We want to make sure that our testing system is pristine,” she said.
Though she supports the lower threshold for confirmatory testing, Brown said there is a cost involved in sending more samples to the reference laboratory. “It’s enough to make us start thinking about whether we want to invest in one of these instruments so we can do the gold standard confirmatory testing here [at St. Louis Children’s],” she said.
Confirmatory testing for metals is typically done by inductively coupled plasma-mass spectrometry (ICP-MS). The laboratory at Virginia Commonwealth University (VCU) Health in Richmond upgraded to ICP-MS several years ago when its graphite furnace atomic absorption spectrometer (GFAAS) stopped working, said Carl Wolf, PhD, forensic toxicology and specialty testing lab supervisor in the VCU department of pathology. “Our reproducibility on the numbers is much better, even at the lower end,” said Wolf, who has performed lead testing for 29 years.
GFAAS works well for detecting lead down to about 2 to 5 µg/dL, but ICP-MS can go as low as 0.1–0.2 µg/dL, according to Wolf. The problem at these low levels is precision, he noted. There will always be some variability between instruments in different laboratories, day-to-day within an instrument, in collection technique, and even the amount of lead in the environment at different times of year. Using U.S. Occupational Safety and Health Administration (OSHA) total allowable error limits of ±4 µg/dL, a reading of 3 µg/dL in one laboratory could be the same as 0 µg/dL or 7 µg/dL in another laboratory. “You can get a number, but do you really know if the number is correct unless you have an understanding of the entire process?” Wolf said. “I think we’re sort of reaching our analytical minimum here. We’re reaching a point where we can’t differentiate normal background from an actual number.”
Meanwhile, Lowry worries that the POC lead test is not always used properly by physicians out in the community. “There are a lot of false positives with those, and that’s not necessarily a lab issue,” Lowry said. For example, a child’s finger needs to be cleaned well before sample collection because a tiny speck of lead on the skin can cause a high reading. Also, a doctor’s office may or may not comply with state laws regarding reporting test results.
One positive development on the POC front is the potential for oral fluid-based testing. Researchers at the Emory University School of Medicine in Atlanta assessed the correlation of oral fluid and blood lead assays and found a negative predictive value for oral fluid of 100% (J Anal Toxicol 2016; doi:10.1093/jat/bkw093). This potentially could have eliminated follow-up blood-based screening in more than half of the 407 children who participated in the study.
Labs’ Role in Follow-Up, Reporting
Another problem in current blood lead testing practice is that sometimes doctors and hospitals fail to follow up positive POC results with confirmatory testing, noted Kenneth Rosenman, MD, professor of medicine and chief of the division of occupational and environmental medicine at Michigan State University in East Lansing. “You’ve now scared the family or the patient, and then they’re not getting the proper follow-up,” Rosenman said. “I see it as a useful screening test if used correctly, but unfortunately in many instances it is not being used correctly.”
Rosenman works with the Michigan Department of Community Health to track blood lead levels in adults, typically related to workplace exposures. After seeing reports of elevated blood lead levels in Flint children, though, he decided to check adults in Flint, even though adults absorb lead less readily than children. “I was surprised to see that there was a bump,” Rosenman said.
A growing body of evidence suggests that, as with children, low levels of lead cause adverse health effects in adults, Rosenman noted. He encourages laboratories to report adult blood lead levels with a reference range based on population norms rather than using the OSHA limits, which he called “outdated.” The upper range of normal at the 95% confidence interval for adult blood lead levels is 5 µg/dL, Rosenman noted.
Another step laboratories should take is to include language in lab reports recommending actions at various blood lead levels, Rosenman suggested, citing guidelines from organizations such as the Council for State and Territorial Epidemiologists or the California Department of Public Health. “I think that’s very useful for doctors, if this is not the usual test they order,” Rosenman said.
There are many things laboratorians can do to prevent lead poisoning—from educating clinicians about the utility of lead tests and creating a workflow that makes it easy for the community to get tested, to seeking funding for community screening programs, Brown emphasized. “We have a role to play in making sure that testing is available to the population that needs it,” she said. “I think as laboratorians, our role is to step up and say, ‘Hey, we can catch this.’ We can come alongside and help prevent a lead crisis from happening in another Flint.”
Julie Kirkwood is a freelance journalist who lives in Rochester, New York. +EMAIL: [email protected]