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Rischitelli G, Nygren P, Bougatsos C, et al. Screening for Elevated Lead Levels in Childhood and Pregnancy: Update of a 1996 U.S. Preventive Services Task Force Review [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2006 Dec. (Evidence Syntheses, No. 44.)

5Discussion

A summary of the evidence for each key question addressed in the evidence synthesis is provided in Table 6. There is fair evidence that screening for elevated lead levels in asymptomatic children at increased risk for lead exposure will improve clinical outcomes. Because there have been no controlled trials directly evaluating screening for elevated lead levels, this conclusion is based on a chain of evidence constructed from studies of weaker design. First, in young asymptomatic children, blood lead levels as low as 10 micro-g/dL and perhaps lower are associated with measurable neurodevelopmental dysfunction. Second, although the national prevalence of elevated lead levels has declined substantially in the past two decades, a high prevalence persists in some communities, particularly poor urban communities in the Northeast and Midwest U.S. Third, measurement of venous blood lead concentration is a reliable, precise and reasonably valid screening test for assessing lead exposure. Fourth, current interventions, including residential lead hazard control and chelation therapy, can reduce blood lead levels in children identified with levels ≥25 micro-g/dL, although the quality of evidence supporting their effectiveness is weak and a beneficial effect on IQ or other clinical outcomes has not yet been demonstrated. Well-designed randomized controlled trials do not support beneficial effects of chelation therapy for asymptomatic children with levels <45 micro-g/dL. There is also weak evidence that screening high-risk children for elevated lead levels results in improved clinical outcome compared to historical controls identified by case finding. Based on this evidence of the current burden of suffering and the effectiveness of early detection, the Task Force recommends screening children at increased risk for lead exposure.

Table 6. Summary of the Evidence.

Table 6

Summary of the Evidence.

While no studies have evaluated a specific age at which to screen, the natural history of blood lead levels in children, which increase most rapidly between 6 and 12 months and peak at age 18–24 months, suggests that screening at about 12 months of age is likely to be most effective for the early detection of elevated lead levels.

For those children who are screened and found to have initial blood lead levels <25 micro-g/dL, there is as yet little evidence regarding the effectiveness of early detection and intervention, or of repeated screening to detect further increases in blood lead. Longitudinal and cross-sectional studies suggest that in children ≥2 years, most such levels will decline naturally with time, but elevated levels may persist in children who are chronically exposed.

There is no direct evidence comparing the outcomes of universal screening with the outcomes from targeted screening for elevated lead levels. Recent studies indicate that the prevalence of elevated blood levels in the U.S. has declined dramatically in the past two decades, but local prevalence is highly variable, with more than tenfold differences between communities. In a community with a low prevalence of elevated blood lead levels, universal screening may result in disproportionate risks and costs relative to benefits. The prevalence level at which targeted screening can replace universal screening is a public health policy decision requiring consideration of factors in addition to the scientific evidence for effectiveness of early detection, such as available resources, competing public health needs, and costs and availability of alternative approaches to reducing lead exposure. Clinicians can consult with their local or state health department regarding appropriate screening policy for the local child population.

In communities where data suggest that universal screening is not indicated, there may nevertheless be some children who are at increased risk of blood lead levels in the range for which individual intervention by chelation therapy or residential lead hazard control has been demonstrated to be effective. In addition to risks from housing, these children may have had exposure to other lead sources such as lead-based hobbies or industries, traditional ethnic remedies, or lead-based pottery. Selective blood lead screening of such high-risk children is appropriate even in low prevalence communities. There is fair evidence that a validated questionnaire of known and acceptable sensitivity and specificity can identify those at high risk. In several studies, the CDC124 and similar questionnaires correctly identified 64% to 87% of urban and suburban children who had blood lead levels ≥10 micro-g/dL. These questionnaires have not been adequately evaluated as a screening tool to detect higher blood lead levels (e.g., ≥20–25 micro-g/dL), or to detect exposure in other populations (e.g., migrant workers, rural communities). Locale-specific questionnaires that inquire about likely local sources of lead exposure may lead to improved prediction.

As is the case in children, there are no controlled trials evaluating screening for elevated lead levels in pregnant women, nor are there sufficient data to construct an adequate chain of evidence demonstrating benefit. The prevalence of levels >15 micro-g/dL appears to be quite low in pregnant women. There is fair evidence that mildly elevated lead levels during pregnancy are associated with small increases in antepartum blood pressure, but limited evidence that these levels have important adverse effects on reproductive or other outcomes, including intelligence of offspring. An extensive literature search failed to identify studies evaluating screening or intervention for lead exposure in pregnant women. There are potentially important adverse effects of chelation therapy on the fetus and of residential lead hazard control on both the pregnant woman and fetus if they are not performed according to established standards. Removal to a lead-free environment would theoretically be effective in reducing lead exposure but has not been specifically evaluated in pregnancy. There is thus insufficient evidence to recommend for or against screening pregnant women for the detection of elevated lead levels.

Community-based interventions for the primary prevention of lead exposure are likely to be more effective, and may be more cost-effective, than office-based screening, treatment and counseling.29 Community, regional, and national environmental lead hazard reduction efforts, such as reducing lead in industrial emissions, gasoline, and cans, have proven highly effective in reducing population blood lead levels.216223 Remaining important sources of lead (e.g., lead paint and pipes in older homes, lead-contaminated soil) are, however, more difficult to address on a population-wide basis. Studies of community-based efforts to reduce lead exposure from these and other sources in order to prevent the occurrence of elevated lead levels are ongoing.23, 158, 224 Evaluation of the effectiveness of community-based interventions, and recommendations regarding their use, are beyond the scope of this document.

Cover of Screening for Elevated Lead Levels in Childhood and Pregnancy
Screening for Elevated Lead Levels in Childhood and Pregnancy: Update of a 1996 U.S. Preventive Services Task Force Review [Internet].
Evidence Syntheses, No. 44.
Rischitelli G, Nygren P, Bougatsos C, et al.

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