Table of Contents

Locator Record

Title: Urinary Mercury (L06UHG_C )
Contact Number: 1-866-441-NCHS
Years of Content: 2003 - 2004
First Published: July, 2007
Revised: NA
Access Constraints: None
Use Constraints: None
Geographic Coverage: National
Subject:Urinary Mercury
Record Source: NHANES 2003 - 2004
Survey Methodology: NHANES 2003 - 2004 is a stratified multistage probability sample of the civilian non-institutionalized population of the U.S.
Medium: NHANES Web site; SAS transport files

Component Description

Mercury is widespread in the environment and originates from natural and anthropogenic sources. The general population may be exposed to three forms of mercury: elemental, inorganic, or organic (primarily methylmercury). The concentration of total mercury in urine is a biomeasure of exposure primarily to elemental and inorganic mercury. Elemental and inorganic mercury exposure can result from mercury spills, dental amalgams, and occupational exposures. Both elemental and inorganic mercury are nephrotoxic and neurotoxic. Health effects related to low exposure in the general population are not well defined. In the 1999-2002 NHANES, urine mercury levels were measured in all women aged 16-49 years. In 2003-2004, urine mercury levels are measured in a one-third subsample of participants aged 6 years and older.

Eligible Sample

Participants aged 6 years and older on an one-third sample.

Description of Laboratory Methodology

Mercury in urine is measured by flow injection cold vapor atomic absorption analysis, which is based on the method that Guo and Bassner (1993) developed. Because mercury in urine is found almost entirely in the inorganic form, Guo and Bassner’s method does not use microwave digestion, and decomposition of mercury compounds is achieved by manually adding mixed bromate-bromide reagent and concentrated hydrochloric acid (HCl). Further decomposition of mercury compounds is achieved by adding potassium permanganate online. The mercury vapor (reduced from inorganic mercury compounds by sodium tetrahydroborate) is measured by the spectrophotometer at 253.7 nm.

Laboratory Quality Assurance and Monitoring

Specimens were processed, stored and shipped to Division of Laboratory Sciences, National Center for Environmental Health, National Centers for Disease Control and Prevention, Atlanta, Georgia.

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed quality control and quality assurance instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).

Read the LABDOC file for detailed QA/QC protocols.

Mobile Examination Centers (MECs)

Laboratory team performance is monitored using several techniques. NCHS and contract consultants use a structured quality assurance evaluation during unscheduled visits to evaluate both the quality of the laboratory work and the quality-control procedures. Each laboratory staff person is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff. Formal retraining sessions are conducted annually to ensure that required skill levels were maintained.

Analytical Laboratories

NHANES uses several methods to monitor the quality of the analyses performed by the contract laboratories. In the MEC, these methods include performing blind split samples collected on “dry run” sessions. In addition, contract laboratories randomly perform repeat testing on 2.0% of all specimens.

NCHS developed and distributed a quality control protocol for all the contract laboratories which outlined the Westgard rules used when running NHANES specimens. Progress reports containing any problems encountered during shipping or receipt of specimens, summary statistics for each control pool, QC graphs, instrument calibration, reagents, and any special considerations are submitted to NCHS and Westat quarterly. The reports are reviewed for trends or shifts in the data. The laboratories are required to explain any identified areas of concern.

There were no changes to the method, site or laboratory from the previous two year cycle.

All QC procedures recommended by the manufacturers were followed. Reported resultsfor all assays meet the Division of Laboratory Science’s quality control and quality assurance performance criteria for accuracy and precision (similar to specifications outlined by Westgard, 1981).

Analytic Notes

Subsample weights

Measures of urinary mercury were measured in a one third subsample of persons 6 years and over. Special sample weights are required to analyze these data properly. Specific sample weights for this subsample are included in this data file and should be used when analyzing these data.

Variance estimation

The analysis of NHANES 2003-2004 laboratory data must be conducted with the key survey design and basic demographic variables. The NHANES 2003-2004 Demographic Data File contains demographic and sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.

Links to NHANES Data Files

This laboratory data file can be linked to the other NHANES 2003-2004 data files using the unique survey participant identifier SEQN.

Detection Limits

Urinary mercury has two detection limits in the data set. Two variables are provided for this analyte. The variable named LBDUHGLC indicates whether the result was below the limit of detection. There are two values: “0”, and “1”. “0” means that the result was at or above the limit of detection. “1” indicates that the result was below the limit of detection.

The other variable named LBX___ provides the analytic result for that analyte. In cases, where the result was below the limit of detection, the value for that variable is the detection limit divided by the square root of two. There are two valid fill values of 0.08 and 0.10.

Please refer to the Analytic Guidelines for further details on the use of sample weights and other analytic issues.

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Target:
Both males and females 6 YEARS - 150 YEARS

URXUHG - Mercury, urine (ng/mL)

Variable Name:
URXUHG
SAS Label:
Mercury, urine (ng/mL)
English Text:
Mercury, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.11 to 75.75 Range of Values 2055 2055
0.1 Fill Value of Limit of Detection 483 2538
. Missing 135 2673

URDUHGLC - Urinary mercury comment code

Variable Name:
URDUHGLC
SAS Label:
Urinary mercury comment code
English Text:
The comment codes associated with the condition of the urinary mercury specimens
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Above the detection limit 2055 2055
1 At or below the detection limit 483 2538
. Missing 135 2673

URXUCR - Creatinine, urine (mg/dL)

Variable Name:
URXUCR
SAS Label:
Creatinine, urine (mg/dL)
English Text:
Creatinine, urine (mg/dL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
6 to 768 Range of Values 2586 2586
. Missing 87 2673

WTSA2YR - Two-year MEC weights of subsample A

Variable Name:
WTSA2YR
SAS Label:
Two-year MEC weights of subsample A
English Text:
Two-year MEC weights of subsample A
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 455771.88304 Range of Values 2673 2673
. Missing 0 2673