Blood testing for elevated lead levels is accurate, but there is not enough evidence to support the screening of asymptomatic pregnant women or asymptomatic children 5 years of age or younger, the U.S. Preventive Services Task Force (USPSTF) has concluded in a final recommendation statement.
The USPSTF, a volunteer group of independent experts that makes evidence-based assessments for disease prevention, published its recommendation statement on screening for elevated blood lead levels in asymptomatic children and pregnant women on its website. The statement and a review of literature on the topic were also published in the Journal of the American Medical Association (April 16, 2019, Vol. 321:15, pp. 1502-1526).
Per the U.S. Centers for Disease Control and Prevention (CDC), the current threshold for elevated lead in the blood is 5 µg/dL. In its statement, the USPSTF noted that "no safe level of lead exposure has been established."
Capillary blood testing is the typical testing method, with confirmation through venous blood testing.
The USPSTF concluded that capillary blood testing "accurately identifies children with elevated blood lead levels."
But the task force also found that the current evidence is insufficient (an "I" grade) when it comes to the accuracy of questionnaires and other tools used to identify those at risk, the harms of screening, and the effectiveness of treatment for elevated blood levels.
The balance of benefits and harms of screening in asymptomatic children and pregnant women cannot be determined, the USPSTF concluded.
Potential harms of screening include adverse events related to chelation therapy treatment, false-positive capillary blood test results, anxiety, and financial costs, the USPSTF explained. Good treatment options are lacking, but identifying elevated lead may help prevent further exposure and identify environmental hazards for a community.
Guidance similar to past advice
The statement is an update of recommendations made in 2006. At that time, the USPSTF found that evidence was insufficient to support routine screening for elevated lead levels in asymptomatic children between the ages of 1 and 5 at increased risk for lead poisoning. Also, at that time, the USPSTF recommended against screening for children ages 1 to 5 at average risk for lead poisoning and against screening for asymptomatic pregnant women.
The USPSTF published a draft recommendation on its updated position statement in October that was open for public comment through December 3. In its April 16 statement, the USPSTF noted that in response to many comments, it included context about at-risk populations and clarified that its recommendations apply to asymptomatic children and women.
In an accompanying JAMA editorial in the same issue (pp. 1464-1465), University of Maryland pediatrics professor Dr. Adam Spanier, PhD, and colleagues said that "for clinicians and child health advocates, the USPSTF recommendation could be viewed as disappointing."
But it is "critical to recognize" that the USPSTF statement does not mean preventive services should not be offered; rather, "it is an acknowledgement that there is insufficient evidence for or against a given service," Spanier's group wrote.
Elevated lead levels are much less of an issue today than in the past. The USPSTF noted that between 1976 and 1980, an estimated 8.8% of children ages 1 to 5 had blood lead levels greater than 10 µg/dL -- formerly used as the threshold -- compared with 0.8% between 2007 and 2010.
However, in an editorial published online April 16 in JAMA Pediatrics, Dr. Michael Weitzman, a professor of pediatrics and environmental medicine at New York University, cautioned that lead still threatens children in the U.S. About half a million have blood levels over 5 µg/dL and one-third of homes have lead-based paint, he noted.
"The inconclusive findings of the new USPSTF recommendation does not mean that screening children for elevated lead levels is not necessary, nor does it shed light on whether screening should be targeted to children at high risk or whether it should be universally done," he wrote. "Only more rigorously conducted research will provide evidence-based answers to these questions."
Assessing capillary blood testing
The USPSTF's latest recommendations are based on a review of 24 studies summarized in an evidence report in the same JAMA issue (pp. 1510-1526) by Dr. Amy Cantor of Oregon Health & Science University and colleagues.
Limitations of the review included "an overall lack of evidence to address all key questions" and a lack of recent data on the effectiveness of risk-based questionnaires -- studies were published between 1994 and 2003 and "may not assess contemporary risk factors," Cantor's group wrote.
A CDC survey with five questions developed in 1991 has traditionally been used to identify those at risk for lead poisoning. However, when it came to identifying children with a venous blood level greater than 10 µg/dL, the questionnaire had pooled sensitivity of just 48% and specificity of 58%. Other questionnaires have not improved upon the accuracy, according to the authors.
Cantor and colleagues also noted that the review "focused on screening and treatment of individuals in primary care settings, excluding community and public health approaches that could inform screening practices at the population level."
The authors were supportive, however, of the testing methods.
"Capillary blood lead testing demonstrated sensitivity of 87% to 91% and specificity greater than 90%, compared with venous measurement," in four studies that were part of the review, Cantor's team wrote.
The slightly worse accuracy of capillary sampling for screening is balanced by advantages of greater convenience and patient preference.
The authors called for more research, including a validated questionnaire for screening children and pregnant women at risk for lead poisoning.
"In lieu of accurate screening instruments, potential alternative strategies include universal screening or screening targeted at communities with a high prevalence of elevated lead levels," Cantor and colleagues suggested.
"Research on newer approaches to detecting elevated blood lead levels, such as point-of-care testing, that include intraindividual and interlaboratory reliability would be useful for assessing screening strategies in children and pregnant women," the USPSTF said in its statement.
Conflicting advice on screening
It's unclear how often screening is being done in children and pregnant women who are asymptomatic, according to the USPSTF.
Similar to the USPSTF, the American Academy of Family Physicians (AAFP) recommends against routine screening for elevated blood lead levels in asymptomatic children at average risk, and it has determined that there is not enough evidence to support screening those at increased risk.
However, other prominent groups back screening, as the USPSTF acknowledged in its statement.
Medicaid requires screening blood lead tests for all young children, and the American Academy of Pediatrics (AAP) supports screening for children at risk for lead poisoning based on their housing, among other factors. The CDC advises screening of children and pregnant women at risk. In addition, the American College of Obstetricians and Gynecologists (ACOG) recommends risk assessments for pregnant women.
Spanier and colleagues pointed out that the "USPSTF must adhere to rigorous methods for evaluation of preventive care services," and they noted the presence of gaps in data on the topic in the pediatric literature.
"Hopefully, third-party payors will consider factors beyond the USPSTF review in determining policies for reimbursement," they wrote.