DATA and STATISTICS
National Report on Human Exposure to Lead
Table 1
Geometric mean and selected percentiles of blood lead concentrations (in g/dL) for the U.S. population, aged 1 year and older, by selected demographic groups, National Health and Nutrition Examination Survey, 1999.
Samplesize Geometricmean(95 %confidenceinterval) Selected percentiles(95% confidence interval) 10th 25th 50th 75th 90th Total, age 1 and older 3,189 1.6 0.7 1.0 1.5 2.3 3.7 (1.4-1.8) (0.6-0.7) (0.9-1.1) (1.4-1.7) (2.2-2.6) (3.2-4.3) Gender Males 1,594 1.9 0.8 1.2 1.8 2.7 4.3 (1.7-2.1) (0.7-0.9) (1.1-1.4) (1.7-2.0) (2.5-3.1) (3.7-5.3) Females 1,595 1.3 0.6 0.8 1.2 1.9 3.0 (1.2-1.5) (0.4-0.7) (0.7-0.9) (1.1-1.4) (1.7-2.1) (2.6-3.5) Race/Ethnicity Black, non-Hispanic 693 1.7 0.8 1.1 1.6 2.5 4.2 (1.5-2.0) (0.6-0.8) (0.9-1.3) (1.4-1.8) (2.2-3.0) (3.3-5.2) Mexican American 1,289 1.8 0.7 1.1 1.6 2.8 4.1 (1.6-2.0) (0.6-0.8) (0.9-1.2) (1.4-1.9) (2.3-3.3) (3.8-5.2) White, non-Hispanic* 1,207 1.5 0.6 1.0 1.5 2.3 3.5 (1.4-1.7) (0.5-0.7) (0.8-1.1) (1.3-1.6) (2.1-2.5) (3.1-4.1) Age group 1-5 years 254 2.0 0.9** 1.3 1.9 2.7 4.7** (1.7-2.3) (0.5-1.1) (1.1-1.5) (1.6-2.1) (2.2-4.4) (3.5-9.8) 6-11 years 419 1.3 0.6 0.8 1.2 1.7 2.7 (1.0-1.6) (0.5-0.7) (0.7-1.0) (1.0-1.5) (1.4-2.2) (1.9-4.7) 12-19 years 868 1.0 0.4 0.6 0.9 1.4 2.1 (0.8-1.2) (0.2-0.5) (0.5-0.8) (0.8-1.1) (1.2-1.6) (1.9-2.4) 20-39 years 595 1.4 0.6 0.8 1.3 2.0 2.8 (1.2-1.5) (0.5-0.7) (0.8-1.0) (1.1-1.5) (1.7-2.2) (2.5-3.2) 40-59 years 471 1.9 0.9 1.2 1.8 2.7 3.8 (1.7-2.0) (0.7-1.0) (1.1-1.3) (1.6-1.9) (2.4-3.2) (3.6-4.4) 60+ years 582 2.5 1.2 1.6 2.3 3.5 5.0 (2.2-2.8) (1.1-1.3) (1.5-1.9) (2.1-2.7) (3.0-4.3) (4.5-6.4)
Numbers in parenthesis are 95% confidence intervals. * includes other race/ethnic groups. ** Estimate meets minimum standards of reliability but should be interpreted with caution.
Table 2
Geometric mean and selected percentiles of urine concentrations and creatinine-adjusted levels for the U.S. population aged 6 years and older, National Health and Nutrition Examination Survey, 1999.
Samplesize Geometricmean(95 %confidenceinterval) Selected percentiles(95% confidence interval) 10th 25th 50th 75th 90th �g/L of urine 1,007 0.80 0.21 0.42 0.80 1.36 2.21 (0.68-0.91) (0.15-0.26) (0.34-0.51) (0.72-0.88) (1.17-1.69) (1.89-2.72) �g/g of creatinine* 1,007 0.72 0.31 0.45 0.69 1.11 1.67 (0.62-0.83) (0.23-0.36) (0.39-0.50) (0.61-0.79) (0.96-1.35) (1.47-2.31)
* �g per gram of creatinine in urine Numbers in parenthesis are 95% confidence intervals.
Interpretation of the lead levels reported in the tables
Blood lead results are presented in Table 1 and urine lead results in Table 2.
Because of lead's adverse effects on cognitive development, CDC has defined an elevated blood lead level as >10 �g/dL for children younger than 6 years of age. Data from CDC's Third National Health and Nutrition Examination Survey (NHANES), Phase 2 (1991-1994) (1) showed that the geometric mean blood lead level for children 1-5 years of old was 2.7 micrograms per deciliter (�g/dL) (95% confidence interval 2.5-3.0 �g/dL). Results in the Report for the same age group for 1999 show that the geometric mean blood lead level has decreased to 2.0 �g/dL (95% confidence interval 1.7-2.3 �g/dL). The sample size in the Report for 1999 is too small to provide reliable estimates of the percentage of children with blood lead levels >10 �g/dL. In future releases of the Report, more blood lead data will be available for this age group, thus permitting reliable estimates of the percentage of children with elevated blood lead levels.
For other age groups and population groups defined by sex and race/ethnicity, the 1999 Report data show consistently lower levels than those measured in the 1991-1994 period (1). The relation of blood lead levels to age is consistent with that seen previously (1).
Elevated blood lead levels among children continue to be a major public health concern.
Table 2 presents urine lead levels. Urine lead is used less frequently to gauge lead exposure. Percentiles provided in Table 2 will serve as reference levels for urine lead so that physicians can compare urine results for individual patients against background levels found in the U.S. population in 1999.
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