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Subclinical lead toxicity, defined as a blood lead level of 10(mu)g/dl or higher, is estimated to affect I in every 20 children in the United States (1). The preponderance of studies demonstrate that low-level lead exposure has serious deleterious and irreversible effects on brain function, such as lowered intelligence and diminished school performance, especially from exposures that occur in early life; hearing deficits and growth retardation have also been observed (2). Collectively, the results of these studies argue that efforts to prevent neurocognitive impairment associated with lead exposure should emphasize primary prevention-the elimination of residential lead hazards before a child is unduly exposed. This contrasts, paradoxically, with current practices and policies that rely almost exclusively on secondary prevention efforts-attempts to reduce a child's exposure to residential lead hazards only after a child has been unduly exposed. Furthermore, despite an abundance of recommendations about how to prevent lead exposure from residential hazards, there is a paucity of data demonstrating the safety or benefits of these recommended controls for children with blood lead levels below 25 (mu)g/dl (3).
Although the mechanisms by which lead causes its toxic effects remain unknown, substantial progress has been made in reducing widespread lead exposure. Before 1970, lead poisoning was defined by blood lead levels greater than 60 (mu)g/dl, a level often associated with acute symptomatic disease, including abdominal colic, frank anemia, encephalopathy, or death. Since then, the threshold for defining elevated blood lead levels has gradually been reduced. In 1991, the Centers for Disease Control (CDC) reduced the threshold even further, to 10 (mu)g/dl (4). During the past two decades, average blood lead levels in U.S. children have fallen by over 90%, largely as a result of the elimination of lead from gasoline and dietary sources (primarily foods and beverages from lead-soldered cans) (5). It is currently estimated that 890,000 (4.4%) preschool children in the United States have a blood lead level of 10 (mu)g/dl or higher (1). In some cities, especially in the northeastern United States, more than 35% of preschool children have blood lead levels exceeding 10 (mu)g/dl from exposure to residential lead hazards (6).
From Screening Children to Housing Universal screening of children for elevated blood lead levels in the United States is controversial. Blood lead levels in...