Uncertainty on Blood Lead Testing

Federal panel finds insufficient evidence to recommend screening average-risk young children, pregnant women.
The U.S. Preventive Services Task Force (USPSTF) has shifted its stance on screening average risk children and pregnant women for lead exposure. Once opposed to screening, this independent panel of primary care and prevention experts is now concluding that there isn’t sufficient evidence to recommend for or against screening in these population groups, regardless of risk factors. As some national entities continue to support universal screening, other subject matter experts caution that USPSTF’s findings do not necessarily advocate an abandonment of screening efforts.
“We encourage all clinicians to use their best medical judgment when making decisions about whether and who to screen, as well as when caring for patients who may have been exposed to lead,” USPSTF Vice Chair Alex Krist, MD, MPH, told CLN Stat. USPSTF’s recommendation statements on these two population groups appear in the Journal of the American Medical Association.
The task force in 2006 had advised against routine screening in pregnant women and in asymptomatic children ages 1 to 5, calling for more research on children at higher risk for lead poisoning. Thirteen years on, the understanding of lead exposure has changed. Currently, no safe level of lead exposure exists, and “the reference level to identify children with elevated blood lead levels has been lowered from 10 μg/dL to 5 μg/dL. Other sources of lead that could affect blood lead levels may now be more prevalent than in 2006, and these sources were not studied in the currently available evidence,” USPSTF wrote in explaining its change of heart in the 2019 update.
To compile evidence on the effectiveness of screening and treatments in these populations, USPSTF looked through several data resources: the Cochrane CENTRAL, the Cochrane Database of Systematic Reviews, and Ovid MEDLINE. It also conducted an active surveillance of any new research through December 2018 that might update current evidence.
USPSTF couldn’t find any studies that evaluated the harms of screening for elevated blood lead levels in children or pregnant women. It also found no evidence that interventions such as counseling, nutrition, and residential lead hazard control techniques reduced blood lead levels in asymptomatic children. It did find that capillary blood testing accurately detected children with elevated blood lead levels. “Capillary blood lead testing demonstrated sensitivity of 87% to 91% and specificity greater than 90%, compared with venous measurement,” USPSTF wrote in its evidence report. Screening questionnaires or clinical prediction tools from the Centers for Disease Control and Prevention (CDC) and other sources were largely unreliable, however.
Chelation treatments seemed to cause more harm than good. One good quality study found a small but significant link between dimercaptosuccinic acid chelation therapy and decreases in height growth and cognitive function in children ages 12 to 33 months with blood lead concentrations between 20 and 44 μg/dL. The therapy has been known to cause a wide range of gastrointestinal systems, headache, hypertension, tachycardia, tremors, fever, and other symptoms.
The effects of lead exposure in younger children and pregnant women can be devastating on growth and development, Krist acknowledged. “Unfortunately, right now there is not enough evidence to tell us what primary care clinicians can do to help prevent and treat the health problems that can result from lead exposure in childhood and pregnancy,” he said.
Krist offered that clinical labs might see a slight increase in typical blood tests for lead exposure, now that USPSTF has eased off from recommending against screening average risk children and pregnant women.
“USPSTF highlights an important conclusion—there are key gaps in the evidence base regarding screening for elevated lead levels,” wrote Adam J. Spanier, MD, PhD, MPH, Pat McLaine, DrPH, RN, and Robyn C. Gilden, PhD, RN, in a related editorial. However, this shouldn’t indicate that screening is obsolete, they and other commentators indicated.
“The statement should serve as rationale for funding agencies to direct resources to the gaps in the literature regarding screening and intervention. It also should encourage clinicians and policymakers to review guidance of other organizations, including state and local public health departments, that might use differing methods for evidence evaluation,” wrote Spanier and colleagues.
The task force’s update represents a significant departure from the more specific recommendations of major medical groups. The American Academy of Family Physicians (AAFP), for instance, recommends against routine screening for elevated blood lead levels in young, asymptomatic children at average risk or in asymptomatic pregnant women.
While AAFP claims the evidence is insufficient to screen high-risk children, the CDC, the Medicaid program, and the American Academy of Pediatrics (AAP) all support universal blood lead testing of children in some capacity. AAP recommends screening in accordance with federal, state, and local requirements, particularly in children who live in areas with a high prevalence of lead hazards, or in high-risk demographic groups such as immigrant or refugee children. AAP’s journal Pediatrics recently reported that young refugee children resettled in the United States are ten times more likely than native children of the same age to have elevated blood lead levels. CDC recommends that refugee children between the ages of 6 months to 16 years get screened upon arrival in the United States, retesting younger children several months after arrival.
The American College of Obstetricians and Gynecologists calls for screening in at-risk pregnant women and blood tests in the event that any of 12 risk factors for lead exposure are found.
For now, the guidance of AAP, CDC, and local, state, and federal regulations “remains indispensable,” wrote Michael Weitzman, MD in a separate commentary in JAMA Pediatrics. “Only more rigorously conducted research will provide evidence-based answers to these questions.”