Lead Exposure in Children: Prevention, Detection, and Management . By 1. 99. 7, the median blood lead concentration in the United States had decreased, and screening in some areas with newer housing turned up few cases of elevated blood lead concentration. The CDC and AAP then began to recommend screening only those children with a greater chance of having an elevated blood lead concentration—those in older housing, those who had a sibling or playmate with an elevated blood lead concentration, or those who had lived in or visited a structure that might contain deteriorated, damaged, or recently remodeled lead- painted surfaces. Screening of all children eligible for Medicaid, among whom were found 8. Health Care Financing Administration (now the Centers for Medicare and Medicaid Services) regulation since 1. This new policy statement replaces the 1. Reliable estimates of the percentage of the US homes containing lead hazards.
Results from a large clinical trial showing that chelation in children with moderately elevated blood lead concentrations does not improve cognitive or neuropsychologic test scores. Documentation of unacceptably low screening rates among Medicaid- eligible children.
Further confirmation of the link between lead exposure in early childhood and delinquent behavior during adolescence. New data showing inverse associations between blood lead concentrations less than 1. In the meantime, case finding, case management, and prevention of additional exposure will still be required.
This document considers relevant aspects of the epidemiology, clinical toxicology, prevention, and treatment of lead exposure in young children and provides recommendations for pediatricians as well as public health authorities. DECLINE OF LEAD POISONING IN THE UNITED STATESLead is an element and occurs naturally, but blood lead concentrations are quite low in the absence of industrial activities. In the United States, there were historically 2 major sources of industrially derived lead for children: airborne lead, mostly from the combustion of gasoline containing tetraethyl lead; and leaded chips and dust, mostly from deteriorating lead paint. Both contribute to soil lead. A steep decrease in exposure to airborne lead in the United States has occurred since 1. Federal legislation in the 1. From 1. 97. 6 to 1.
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US children 1 to 5 years of age had a median blood lead concentration of 1. Airborne lead should no longer be a source of community exposure in the United States, but individual counties sometimes still exceed airborne lead regulations, and continued vigilance is warranted. Individual children may still be exposed to airborne lead in fumes or respirable dust resulting from sanding or heating old paint, burning or melting automobile batteries, or melting lead for use in a hobby or craft. SOURCES OF LEAD EXPOSURELead Paint, Dust, and Soil.
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The source of most lead poisoning in children now is dust and chips from deteriorating lead paint on interior surfaces. Children who developed lead encephalopathy with blood lead concentrations more than 1.
Children who live in homes with deteriorating lead paint, however, can achieve blood lead concentrations of 2. However, in 1. 99. US homes with . Lead in dust and soil can recontaminate cleaned houses. Transplacental Exposure and Lead in Human Milk. Lead crosses the placenta, and the blood lead concentration of the infant is similar to that of the mother. The source of lead in the infant's blood seems to be a mixture of approximately two thirds dietary and one third skeletal lead, as shown by studies that exploited the differences in lead isotopes stored in the bones of women migrating from Europe to Australia.
Although lead appears in human milk, the concentration is closer to plasma lead and much lower than blood lead, so little is transferred. Because infant formula and other foods for infants also contain lead, women with commonly encountered blood lead concentrations who breastfeed their infants expose them to slightly less lead than if they do not breastfeed. In Mexico, giving women supplemental calcium during lactation resulted in a small (less than 2 . In the United States, however, where calcium intake may be higher, calcium supplementation does not prevent bone loss during lactation. Other Sources. Lead plumbing (in Latin, “plumbus” = lead) has contaminated drinking water for centuries, and lead in water can contribute to elevated blood lead concentrations in children.
In 2. 00. 3–2. 00. Washington, DC, was found to exceed Environmental Protection Agency (EPA) regulations.
This was thought to be caused by a change in water disinfection procedures, which increased the water's ability to leach lead from connector pipes between the water mains and interior plumbing in old houses. The extent of this problem in Washington and other cities is not yet known. Affected families are drinking filtered or bottled water until the pipes can be replaced. Such questions may be useful if a child has an elevated blood lead concentration but no exposure to leaded dust or soil. They have not been validated for the purpose of deciding whether to screen. TABLE 1. Suggested Clinical Evaluation for Lead Exposure. The lead concentration of blood for transfusion is not routinely measured.
After exchange transfusion in the extremely low birth weight infant, 9. Bearer et al. 22 recommended that only units with lead concentrations of less than 0. Approximately one third of the units of blood that they measured were above this concentration. The effect of lead in transfused blood used in older children has not been considered. TOXICITY OF LEADSubclinical Effects. At the levels of lead exposure now seen in the United States, subclinical effects on the central nervous system (CNS) are the most common effects. The best- studied effect is cognitive impairment, measured by IQ tests.
The strength of this association and its time course have been observed to be similar in multiple studies in several countries. In most countries, including the United States, blood lead concentrations peak at approximately 2 years of age and then decrease without intervention. Blood lead concentration is associated with lower IQ scores as IQ becomes testable reliably, which is at approximately 5 years of age. The strength of the association is similar from study to study; as blood lead concentrations increase by 1. Canfield et al. 7 recently extended the relationship between blood lead concentration and IQ to blood lead concentrations less than 1. They observed a decrease in IQ of more than 7 points over the first 1.
Bellinger and Needleman. Canfield et al study. To confirm the adverse effects of lead on IQ at these concentrations, however, more children whose blood lead concentration has never been more than 1. A reanalysis of the primary data from several of the prospective studies is underway to help resolve this issue. At the moment, however, these data have not yet been incorporated into policy, and the CDC1. AAP2. 4 both currently use 1.
Teachers reported that students with elevated tooth lead concentrations were more inattentive, hyperactive, disorganized, and less able to follow directions. Additional follow- up of some of those children.
Elevated bone lead concentrations are associated with increased attentional dysfunction, aggression, and delinquency. In children followed from infancy with blood lead measurements, self- reported delinquent behavior at 1. These data imply that the effects of lead exposure are long lasting and perhaps permanent. Subclinical effects on both hearing.
Although there are reasonable animal models of low- dose lead exposure and cognition and behavior,3. CNS function are not known. Lead alters very basic nervous system functions, such as calcium- modulated signaling, at very low concentrations in vitro,3.
Lead interferes detectably with heme synthesis beginning at blood lead concentrations of approximately 2. Ferrochelatase inhibition is the basis of an erstwhile screening test for lead poisoning that measures erythrocyte protoporphyrin (EP), the immediate heme precursor. Because it is insensitive to the lower concentrations of blood lead that are of concern now, the test is obsolete for that use; however, EP measurement is still used clinically in managing children with higher blood lead concentrations. Clinical Effects. Children with blood lead concentrations greater than 6. These are premonitory symptoms of CNS involvement and may rapidly proceed to vomiting, stupor, and convulsions. Symptomatic lead toxicity should be treated as an emergency.
Although lead can cause clinically important colic, peripheral neuropathy, and chronic renal disease in adults with occupational exposures, these symptoms are rare in children. Reversibility. In an influential 1.
Those whose blood lead concentrations decreased the most had improved cognitive test scores independent of whether they had been given iron or chelation therapy. An Australian study. IQs of children whose blood lead concentrations decreased the most. A large (7. 80- children) randomized trial of the use of succimer in children with blood lead concentrations of 2. The children were randomly assigned at approximately 2 years of age and followed with cognitive, neuropsychologic, and behavioral tests until they were approximately 5 years of age. The large size of the trial permits confident exclusion of a drug- related improvement of 2 IQ points or more. Additional follow- up at 7 years of age with more sophisticated testing still showed no advantage for the succimer- treated children.
Because blood lead concentrations decreased as the children in the TLC Trial got older regardless of whether they had chelation, Liu et al. TLC data to attempt to replicate the reported relationship between decreasing blood lead concentrations and improved cognitive test scores. Test scores were unrelated to decreasing blood lead concentrations at 6 months' follow- up, but results from following the children for 3.