Table of Contents

Component Description

Blood mercury: inorganic, ethyl and methyl

Uncertainties exist regarding levels of exposure to methyl mercury from fish consumption and potential health effects resulting from this exposure. Past estimates of exposure to methyl mercury have been obtained from results of food consumption surveys and measures of methyl mercury in fish. Measures of a biomarker of exposure are needed for improved exposure assessments.

Blood measures of total and inorganic mercury will be important for evaluating exposure to mercury in interior latex paints.

Eligible Sample

Examined participants, aged 1 year and older and aged 12 years and older in a one-half sample, were eligible.

Description of Laboratory Methodology

Inorganic, Ethyl and Methyl Mercury

The mercuries in blood are measured using stannous chloride as a reductant, also utilizing microwave digestion. Mercury vapor (reduced from inorganic mercury compounds) is measured via the same quartz cell at 253.7 nm.

The difference between total and inorganic mercury represents the organic mercury in blood. Mercury analysis identifies cases of mercury toxicity. The main organs affected by mercury are the brain and kidneys. Psychic and emotional disturbances are the initial signs of chronic intoxication by elemental mercury vapor or salts. Parasthesia and neuralgia may develop. Renal disease, digestive disturbances, and ocular lesions can also develop. Kidney toxicity is an important consequence of exposure to mercury salts.

Refer to the Laboratory Method Files section for detailed laboratory procedure manual(s) of the methods used.

There were no changesto equipment, lab methods, or lab site.

Laboratory Method Files

Laboratory Quality Assurance and Monitoring

Blood specimens are processed, stored, and shipped to the Division of Laboratory Sciences, National Center for Environmental Health, and Centers for Disease Control and Prevention, Atlanta, GA for analysis.

Detailed instructions on specimen collection and processing are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials are stored under appropriate frozen (–70°C) conditions until they are shipped to National Center for Environmental Health for testing.

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

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 (Westgard et al, 1981) 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 quarterly. The reports are reviewed for trends or shifts in the data. The laboratories are required to explain any identified areas of concern.

All QC procedures recommended by the manufacturers were followed. Reported results for all assays meet the Division of Laboratory Sciences’ quality control and quality assurance performance criteria for accuracy and precision, similar to the Westgard rules Caudill, et al., 2008). 

Data Processing and Editing

The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

Three calculated variables were created in this data file. The formula for their derivation is as follows:

LBXIHG and LBDIHGSI
The inorganic mercury in µg/L was converted to nmol/L by multiplying by 4.99.

LBXBGE and LBDBGESI
The ethyl mercury in µg/L was converted to nmol/L by multiplying by 4.99.

LBXBGM and LBDBGMSI
The methyl mercury in µg/L was converted to nmol/L by multiplying by 4.99.

Analytic Notes

Refer to the 2013-2014 Laboratory Data Overview for general information on NHANES laboratory data.

Demographic and Other Related Variables

The analysis of NHANES 2013-2014 laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2013-2014 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample weight variables. The Fasting Questionnaire File includes auxiliary information, such as fasting status, the time of venipuncture, and the conditions precluding venipuncture. The demographics and fasting questionnaire files may be linked to the laboratory data file using the unique survey participant identifier (i.e., SEQN).

Subsample Weights

These analytes were measured in a one half subsample of participants aged 12 years and older. 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.

Exam Sample Weights

Exam sample weights should be used for analyses for participants aged 1 to 11 years.

The lower limit of detection (LLOD, in µg/L):

Analyte

Item ID

LLOD

LBXIHG

Mercury, inorganic

0.27

LBXBGE

Mercury, ethyl

0.16

LBXBGM

Mercury, methyl

0.12

 

Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial 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 1 YEARS - 150 YEARS

WTSH2YR - Blood metal weights

Variable Name:
WTSH2YR
SAS Label:
Blood metal weights
English Text:
Blood metal weights
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
4533.45942 to 322113.58855 Range of Values 5766 5766
0 No lab samples 166 5932
. Missing 0 5932

LBXIHG - Mercury, inorganic (ug/L)

Variable Name:
LBXIHG
SAS Label:
Mercury, inorganic (ug/L)
English Text:
Inorganic mercury, blood (ug/L)
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.19 to 13 Range of Values 5175 5175
. Missing 757 5932

LBDIHGSI - Mercury, inorganic (umol/L )

Variable Name:
LBDIHGSI
SAS Label:
Mercury, inorganic (umol/L )
English Text:
Mercury, inorganic (umol/L )
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.95 to 64.87 Range of Values 5175 5175
. Missing 757 5932

LBDIHGLC - Mercury, inorganic comment code

Variable Name:
LBDIHGLC
SAS Label:
Mercury, inorganic comment code
English Text:
Mercury, inorganic comment code
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 900 900
1 Below lower detection limit 4275 5175
. Missing 757 5932

LBXBGE - Mercury, ethyl (ug/L)

Variable Name:
LBXBGE
SAS Label:
Mercury, ethyl (ug/L)
English Text:
Mercury, ethyl (ug/L)
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.11 to 0.66 Range of Values 5175 5175
. Missing 757 5932

LBDBGELC - Mercury, ethyl comment code

Variable Name:
LBDBGELC
SAS Label:
Mercury, ethyl comment code
English Text:
Mercury, ethyl comment code
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 43 43
1 Below lower detection limit 5132 5175
. Missing 757 5932

LBXBGM - Mercury, methyl (ug/L)

Variable Name:
LBXBGM
SAS Label:
Mercury, methyl (ug/L)
English Text:
Mercury, methyl (ug/L)
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.08 to 47.15 Range of Values 5175 5175
. Missing 757 5932

LBDBGMLC - Mercury, methyl comment code

Variable Name:
LBDBGMLC
SAS Label:
Mercury, methyl comment code
English Text:
Mercury, methyl comment code
Target:
Both males and females 1 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 3855 3855
1 Below lower detection limit 1320 5175
. Missing 757 5932