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Children’s
Blood Lead Levels in the United States |
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Tracking
blood lead levels |
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Defining
the problem |
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National
surveys |
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State
and local surveillance |
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Prevalence
surveys |
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Next
steps |
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Tracking
blood lead levels
The
Centers for Disease Control and Prevention (CDC) tracks children’s
blood lead levels (BLLs) in the United States using three methods: (1)
nationally representative surveys (2) state and local surveillance and
(3) local prevalence surveys. Because lead exposure in children varies among populations
and communities, all three approaches are needed to understand the
burden of elevated BLLs among young children across the United States.
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Together,
the three data sources enable CDC to describe children at risk and to
measure trends in BLLs among young children.
Special attention is given to BLLs >=10
micrograms per deciliter (µg/dL).
Many studies point to a link between BLLs >=10
µg/dL
and harmful health effects, in particular learning disabilities and
behavior problems. The Department of Health and Human Services’ Healthy
People 2010 initiative has set a national goal of eliminating BLLs
>=10
µg/dL
among children aged 1-5 years by 2010.
CDC also tracks BLLs in adults using NHANES and state
surveillance (ABLES)
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The National Health and Nutrition Examination Surveys (NHANES), conducted by CDC's National Center for Health Statistics, have been tracking BLLs in the United States since the 1970s (NHANES). These national surveys are designed to estimate BLLs at the national level only not at the state or local levels. NHANES have documented a substantial decrease in BLLs among young children. The NHANES II 1976-1980 reported a geometric mean BLL of 15 µg/dL among children aged 1-5 years. The most current NHANES (1999-2000) data show that geometric mean BLLs continue to decrease in young children.
BLLs >=10 µg/dL were estimated for 2.2% of children aged 1-5 years according to NHANES 1999-2000. The 2.2% estimate translates to 434,000 children with a 95% confidence interval from 189,000 to 846,000 children. This confidence interval means that there is a 95% probability that the true number is within that range. Future NHANES should help confirm the trends shown in Table 1.
Table 1. NHANES Blood Lead Level Measurements for Children Aged 1-5
Years by Year of NHANES, United States
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| Year |
Geometric
Mean1 BLLs (95%
CI2) |
Prevalence3
of BLLs >=10 µg/dL4
(95% CI) |
Estimated
Number of Children with BLLs >=10µg/dL
(95% CI) |
| 1976
- 1980 |
14.9
(14.1 - 15.8) |
88.2%
(83.8 - 92.6) |
13,500,000
(12,800,000 - 14,100,000) |
| 1988
- 1991 |
3.6
(3.3-4.0) |
8.6%5
(4.8-12.4%) |
1,700,000
(960,000-2,477,000) |
| 1991
- 1994 |
2.7
(2.5-3.0) |
4.4%
(2.9-6.6%) |
890,000
(590,000-1,330,000) |
| 1999
- 2000 |
2.2
(2.0-2.5) |
2.2%
(1.0-4.3%) |
434,0006
(189,000-846,000) |
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1
A
measure of central tendency that differs from an arithmetic mean
because it uses multiplication rather than addition to summarize the
data values
2 This confidence
interval (CI) means that there is a 95% probability that the true
number is within that range
3 The number of children
with BLLs >=10 µg/dL
over the whole population at a given point in time
4 CDC has
determined a blood lead level (BLL) 10 micrograms per deciliter (µg/dL) to be a level of concern
5 This
estimate differs slightly from values published previously due to
updates in coding and weighting of the survey data.
6 This
estimate differs slightly from values published previously due to weighting of the survey data.
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State
and local surveillance
To
obtain state and local estimates, CDC supports state and local child
blood lead surveillance systems.
Many states target their screening resources to children
considered at highest risk. This
approach makes good use of limited funds but does not necessarily
produce data representative of all children aged 1-5 years.
Therefore, estimates obtained from state and local surveillance
data cannot be directly
compared to NHANES.
State
surveillance data show that the risk for BLLs >=10
µg/dL
in children tested remains high in some counties and varies greatly
among states. Analysis of data from 19 states that received all BLLs
of children from laboratories for calendar years 1996 through 1998
have shown that the proportion of children with BLLs >=10
µg/dL
among those tested for lead by state ranged from 2.7% to 14.9%.
Within individual states the proportion of children with BLLs >=10
µg/dL,
among those tested, varied considerably.
For example, in Ohio, the range of the proportion of BLLs >=10
µg/dL
among children tested ranged from 1.3% in one county to 27.3% in
another. Across all 19
states, the county-specific proportions of children with BLLs >=10
µg/dL
ranged from 0.5% to 27.3%. (MMWR
2000). |
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Prevalence
surveys
CDC
supports local prevalence studies that are representative of the area
studied. A study in
Chicago found that in one community, more than 20% of the children
aged 1-5 years had BLLs >=10
µg/dL.
Other state and local health departments are making plans to conduct
similar studies to assess the extent of the problem in high risk
communities.
Prevalence
studies provide the best local estimates of children with BLLs >=10
µg/dL;
however, these studies involve the time and effort of many people.
For this reason, prevalence studies may be useful in areas
suspected to have a large number of families at high risk for BLLs >=10
µg/dL,
such as those families who have low incomes, who live in pre-1950
deteriorated housing, and who are minorities. |
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Next
steps
Specifically,
CDC will place more emphasis on state and local surveillance to
understand the burden of BLLs >=10
µg/dL
among young children. CDC
will increase efforts to improve the quality of state and local
surveillance data and to share findings.
A report on state surveillance data is planned for summer 2003.
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