Blood Lead Level

Lead is a naturally occurring metal found in small amounts in rock and soil. Lead has been used industrially in the production of gasoline, ceramic products, paints, metal alloys, batteries, and solder. While lead arising from the combustion of leaded gasoline was a major source of exposure in past decades, today deteriorated lead-based paint, and resulting dust and soil contamination are the primary sources of environmental lead exposure (CDC, 2009).

Lead is a neurotoxic metal that affects areas of the brain that regulate behavior and nerve cell development (NRC, 1993). Its adverse effects range from subtle responses to overt toxicity, depending on how much lead is taken into the body and the age and health status of the person (CDC, 1991). Lead is one of the few pollutants for which biomonitoring and health effect data are sufficient to clearly evaluate environmental management efforts to reduce lead in the environment.

Children, infants, and fetuses are more vulnerable to the effects of lead because the blood-brain barrier is not fully developed in them (Nadakavukaren, 2000). Thus, a smaller amount of lead will have a greater effect on children than on adults. In addition, lead absorption can be up to five times greater in children compared to adults. Up until May 2012, the Centers for Disease Control and Prevention (CDC) had defined an elevated blood lead level as equal to or greater than 10 micrograms per deciliter (µg/dL) for children under 6 years of age. Because of growing scientific evidence of adverse effects of blood lead levels below 10 µg/dL in children, CDC adopted a “reference value” for lead based on the 97.5^th percentile of the blood lead level distribution in U.S. children aged 1–5 years, which currently is 5 µg/dL (CDC, 2012).

This indicator is based on data collected by the National Health and Nutrition Examination Survey (NHANES). NHANES is a series of surveys conducted by CDC’s National Center for Health Statistics that is designed to collect data on the health and nutritional status of the civilian, non-institutionalized U.S. population using a complex, stratified, multistage, probability-cluster design. CDC began monitoring blood lead in 1976 as part of NHANES II, which covered the period from 1976 through 1980. Blood lead was also monitored in NHANES III, which covered the period between 1988 and 1994. CDC’s National Center for Environmental Health conducted the laboratory analyses for the biomonitoring samples. Beginning in 1999, NHANES became a continuous and annual national survey.

Blood lead levels have declined steadily since NHANES surveillance of blood lead levels across the U.S. began in 1976. NHANES II (1976-1980) reported that 88.2 percent of children age 1 to 5—the population at the highest risk for lead exposure and effects—had blood lead levels greater than or equal to 10 µg/dL. The largest reduction in children’s blood lead levels was seen between NHANES II and the first phase of NHANES III (1988-1991), when the prevalence of blood lead levels greater than or equal to 10 µg/dL decreased to 8.9 percent (CDC 1994; Meyer et al., 2003). Data collected from 1991 to 1994 as part of the second phase of NHANES III showed a continual decrease, with 4.4 percent of children age 1 to 5 having blood lead levels greater than or equal to 10 µg/dL (CDC, 2009). The data presented here cover seven different survey periods from the continuous survey: 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, 2009-2010, and 2011-2012.

The geometric mean blood lead levels among all participants age 1 year and older ranged from 0.973 µg/dL (2011-2012) to 1.66 µg/dL (1999-2000) (Exhibit 1). During the most recent survey (2011-2012), 5 percent of those age 1 or older exhibited blood lead levels of 3.16 µg/dL or greater (Exhibit 1).

Blood lead levels were consistently higher in males than females. In the 2011-2012 survey, males and females had geometric mean lead levels of 1.13 µg/dL and 0.842 µg/dL, respectively (Exhibit 1). For non-Hispanic blacks, Mexican Americans, and non-Hispanic whites in the 2011-2012 survey, the geometric mean lead levels were 0.998, 0.838, and 0.993 µg/dL, respectively. These demographic groups exhibited similar decreases in blood lead levels between 1999-2000 and 2011-2012 (Exhibit 2).

In the 2011-2012 survey, adults 20 years and older had the highest geometric mean blood lead level (1.09 µg/dL) of all the reported age groups. This was followed by the geometric blood lead level of children 1 to 5 years of age (0.970 µg/dL), which was the age group with the highest level for all survey periods from 1999-2000 to 2007-2008. Next was children 6 to 11 years of age (0.681 µg/dL) and children 12 to 19 years of age (0.554 µg/dL) (Exhibit 3). Blood lead levels generally declined in all age groups throughout the 1999-2012 survey period, with the largest decrease seen among children 1 to 5 years of age (2.23 µg/dL [1999-2000] to 0.970 µg/dL [2011-2012]) (Exhibit 3).

• The relatively small number of samples collected in a two-year cycle (e.g., 1999-2000 or 2001-2002) may, in some cases, result in measures of central tendency that are unstable from one survey period to the next.

Data used for this indicator were obtained directly from CDC’s Fourth National Report on Human Exposure to Environmental Chemicals, Updated Tables, August 2014 (CDC, 2014).