• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Data Processing and Editing
• Laboratory Quality Assurance and Monitoring
• Analytic Notes
• References
• Codebook
  • POOLID - Pool ID number
  • RIAGENDR - Gender
  • RIDRAETN - Ethnicity
  • RIDAGGRP - Age Group
  • RIANSMP - Number of samples included in Pool
  • SSHCB - HCB
  • SSBHC - B-HCCH
  • SSGHC - G-HCCH
  • SSOXY - OXYCHLOR
  • SSTNA - T-NONA
  • SSPDE - PP-DDE7
  • SSODT - OP-DDT
  • SSPDT - PP-DDT
  • SSMIR - MIREX

National Health and Nutrition Examination Survey

2001-2002 Data Documentation, Codebook, and Frequencies

Pesticides - Organochlorine Metabolites - Serum - Pooled Samples (Surplus) (SSPST_B)

Data File: SSPST_B.xpt

First Published: July 2013

Last Revised: NA

Component Description

Organochlorine pesticides are a diverse group of synthetic chemicals that persist in the environment and tend to bioaccumulate. Most of these chemicals have been banned from use in the U.S. Assessment of exposure to persistent organochlorine pesticides in a representative sample of the U.S. population is needed to determine current prevalence and level of exposure and the potential for human health effects from exposure to these chemicals.

Eligible Sample

Study participants aged 3 years and older from NHANES 2001 - 2002 with stored serum available to prepare pooled samples.

Description of Laboratory Methodology

Nine organochlorine pesticides and metabolites were measured in serum by gas chromatography/isotope-dilution high-resolution mass spectrometry (GC/ID-HRMS). The analytical method for organochlorine pesticides is described in Sjodin et al., 2004 and Barr et al., 2003. Reported results met the Division of Laboratory Sciences’ quality control and quality assurance performance criteria for accuracy and precision (similar to specifications outlined by Westgard, 1981).

Data Processing and Editing

Specimens were processed, stored, and shipped to DLS, NCEH, CDC (Atlanta, Georgia). The analytical approach used, including data processing is described in detail in Sjodin, et al (2004). Reported results met the Division of Laboratory Sciences’ quality control and quality assurance performance criteria for accuracy and precision (similar to specifications outlined by Westgard, 1981).

Laboratory Quality Assurance and Monitoring

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

Read the General Documentation on Laboratory Data file for detailed QA/QC protocols.
 
The analytical methods are described in the Description of the Laboratory Methodology section.

Analytic Notes

The sampling scheme for NHANES 2001–2002, a complex multistage area probability design, included 11,039 persons. Data were collected through household interviews and through standardized physical examinations conducted in mobile examination centers. On the basis of self-reported data, a composite race/ethnicity variable helped define three major racial/ethnic groups: non-Hispanic blacks, non-Hispanic whites, and Mexican Americans. Informed consent was obtained from all study participants. Serum samples used to prepare pools for analysis were selected from those obtained by venipuncture from 2150 participants, a random one-third subsample of people 12 years of age and older from NHANES 2001-2002 and representative of the U.S. general population for this age range. A total of 1,832 individual serum samples were used to prepare the 54 pooled serum samples analyzed for this subset of NHANES 2001-2002.

After collection of samples, serum specimens were divided into aliquots and were stored cold (2–4°C) or frozen until they were shipped on dry ice to CDC’s National Center for Environmental Health (NCEH). Serum samples were stored frozen after receipt at NCEH at –70°C until analyzed. The 2,150 individual serum samples available were categorized in 24 demographic groups (Table 1), each representing a combination of race/ethnicity, gender, and age (12–19 years, 20–39 years, 40–59 years, and 60 years and older). The number of samples available, the number of these samples that were usable, and the number of pools formed in each demographic group are presented in Table 1. On the basis of the number of individual serum samples per demographic group, multiple pools were available for 14 demographic groups, and one pool was available for 10 demographic groups (Table 1). To ensure that no individual sample overly influenced the pooled results, all serum samples included in any one pool (25.5 mL each) were of equal volume (i.e., each individual sample contributed 750 μL). Most pools included 34 individual serum samples that were randomly selected. Only 31 individual serum samples were available, however, for the pool representing non-Hispanic black men 60 years of age or older. In addition, one of the two pools representing Mexican American men between 20 and 39 years of age consisted of only 33 individual specimens.

In addition, residual serum from 3–11 year old NHANES 2001–2002 participants, previously analyzed for cotinine, a marker of environmental tobacco smoke, was used to create pools representing 3-5 year old and 6-11 year old partisipants. The 1049 individual samples available were categorized in 12 demographic groups, each representing a combination of race/ethnicity, sex, and age (3–5 years and 6–11 years). A total of 937 randomly selected individual samples were used to prepare 24 pools (two per demographic group). The number of samples available, the number of these samples that were usable, and the number of pools formed in each demographic group are presented in Table 1. To ensure that no individual sample overly influenced the pooled results, all samples included in any one pool were of equal volume (i.e., 0.5 mL). Eleven of the individual serum samples from non-Hispanic black females 3–5 years of age contributed <0.5 mL. Each pool included 21 (3–5 year old) or 57 (6–11 year old) individual samples randomly selected (Table 1).

Table 1. Number of individual serum samples available, number of usable samples, and number of pools formed from NHANES 2001–2002 participants per demographic group.

Guidelines for Working with Pooled-Samples from NHANES 2001-2002

Because the samples constituting the pools originated from NHANES 2001-2002, which was designed to be representative of the non-institutionalized US population, the pooled results should provide good coverage of the US population. We cannot be assured, however, that estimates based on the pooled samples are unbiased for at least two reasons: 1) the sampling weight information was lost when the samples were pooled because each pool consists of equal volumes of each sample in the pool; and 2) the measured value for a pooled sample (consisting of individual samples that tend to be log-normally distributed) is comparable to an arithmetic average of log-normal results and thus represents a biased estimate of the central tendency (geometric mean or median) of the samples making up the pool. Also, because samples were pooled across the design cells of the original NHANES sampling design, it is not possible to obtain unbiased estimates of standard errors. These bias and standard error issues are being addressed in later NHANES surveys involving pooled samples.

Pooled-Sample weights

The sampling weight information was lost when the samples were pooled because each pool consists of equal volumes of each sample in the pool.

Variance estimation

The sampling scheme for NHANES 2001–2002 is a complex multistage, probability sampling design that selects participants who are representative of the civilian, non-institutionalized U.S. population. Over-sampling of certain population subgroups is done to increase the reliability and precision of health status indicator estimates for those groups. For Organochlorine pesticides, instead of using the full NHANES sample, a random one-third subsample of NHANES participants was used. Curtin et al. (2012) provide documentation of the construction of sampling weights for this one-third subsample. Also, because of the use of stratified multistage selection, incorporation of the sampling design is needed to calculate sampling variances (NCHS, 1994). These variances cannot be calculated for NHANES 2001-2002 pooled sample estimates, however, because samples were pooled across the design cells of the original NHANES 2001-2002 sampling design.

Links to NHANES Data Files

Although this pooled-sample data file cannot be directly linked to other NHANES 2001-2002 data files, it does contain demographic information (RIAGENDR, RIDRAETN, and RIDAGGRP) for each pooled-sample.

Variables in the data file

Each variable in the data file is given in Table 2 with its definition. The definition used for the numeric constant for categorical variables is given in the column: Definition of Categorical Variables.

The NHANES abbreviation used for each analyte measured with the IUPAC name is given in Table 3. The code “XYZ” in the variable names “ADJUSTED_RESULT_XYZ” and “RESULT_COMMENT_XYZ” as defined in Table 2 corresponds to the Value of the “NHANES code” in Table 3.

 

Table 2. NHANES Code, Common Abbreviation and IUPAC Name for each analyte reported

Variable	Description	Definition of Categorical Variables
POOLID	Pool identification number	n/a
RIAGENDR	Gender of subjects in pool	1 = Male
		2 = Female
RIDRAETN	Race / Ethnicity of subjects in pool	1 = Non-Hispanic White (NHW)
		2 = Non-Hispanic Black (NHB)
		3 = Mexican American (MA)
RIDAGGRP	Age group of subjects in pool	-1 = 3-5 Year old
		0 = 6-11 Year old
		1 = 12-19 Year old
		2 = 20-39 Year old
		3 = 40-59 Year old
		4 = >60 Years old
RIANSMP	Number of samples pool	n/a
ADJUSTED_RESULT_XYZ	Reported Concentration (ng/g lipid). "XYZ" in the variable name corresponds to the NHANES abbreviation for each analyte.	n/a
RESULT_COMMENT_XYZ	Code for measured concentration. "XYZ" in the variable name corresponds to the NHANES abreviation for each analyte	0 = Detectable Result 30 = Non-Reportable Result 37 = Result having a concentration below the limit of detection. The value for the variable "ADJUSTED_RESULT_XYZ" for this analyte corresponds to the limit of detection divided with the square root of 2.

 

 

Table 3. NHANES Code, Common Abbreviation and IUPAC Name for each analyte reported

NHANES CODE	Common Abbreviation	IUPAC Name
HCB	HCB	Hexachlorobenzene
BHC	B-HCCH	beta-Hexachlorocyclohexane
GHC	G-HCCH	gamma-Hexachlorocyclohexane
OXY	OXYCHLOR	Oxychlordane
TNA	T-NONA	trans-Nonachlor
PDE	PP-DDE	p,p'-Dichlorodiphenyldichloroethylene (p,p'-DDE)
ODT	OP-DDT	o,p'-Dichlorodiphenyltrichloroethane (o,p'-DDT)
PDT	PP-DDT	p,p'-Dichlorodiphenyltrichloroethane (p,p'-DDT)
MIR	MIREX	Mirex

References

• Barr JB, Maggio VL, Barr DB, Turner WE, Sjodin A, Sandau CD, et al. New high-resolution mass spectrometric approach for the measurement of polychlorinated biphenyls and organochlorine pesticides in human serum. J Chromatogr B 2003;794(1):137-48.
• Sjodin A, Jones RS, Lapeza CR, Focant J-F, McGahee EE III, Patterson DG Jr. Semiautomated high-throughput extraction and cleanup method for the measurement of polybrominated diphenyl ethers, polybrominated biphenyls, and polychlorinated biphenyls in human serum. Anal. Chem. 2004; 76:1921-7.
• Westgard JO, Barry PL, Hunt MR, Groth T. 1981. A multi-rule Shewhart chart for quality control in clinical chemistry. Clin Chem 27: 493-501.

Codebook and Frequencies