Elevated blood lead levels (EBLLs) are one of the major environmental problems presently facing children in the United States and elsewhere. In 1991, the Centers for Disease Control and Prevention (CDC) identified 10 μg/dL as an EBLL that should prompt public health actions to identify and manage exposure to lead. (A commonly referenced unit of measure is the blood lead value in μg/dL (micrograms per deciliter); 10 μg/dL is equivalent to 0.48 μmol/L (micromoles per liter); the conversion factor of 0.04826 is multiplied by the lead value in μg/dL to give the lead value in μmol/L.) The level had been reduced from 40 in 1971 to 10 in 1991. It has also been termed a “level of concern,” which is an unfortunate wording because there has been concern about harmful effects below this level since before 1991. In addition, this level was never seen as a threshold level (a level below which adverse effects would not occur). Older terms, lead toxicity and lead poisoning, were less specific, and generally referred to adverse or toxic effects from lead exposure that were not specific to a particular blood lead level (BLL).

The prevalence of EBLLs has decreased dramatically for the entire population and for children aged 1–5 years in the United States. Data from the National Health and Nutrition Examination Surveys (NHANES) show a decline in the geometric mean (average) BLLs from 15.2 (1976–1980) to 1.9 (1999–2002), with a similar decline in the prevalence (or percentage) of children with BLLs of 10 μg/dL or higher from 88.2% to 1.6% over the same time periods. Although the numbers have decreased significantly, this still represents an estimated 310,000 children with BLLs in this category.