Table of Contents

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

Examined participants aged 12 years and older from a one-third sample were eligible.

Description of Laboratory Methodology

Serum samples from NHANES 2009-2010 were stored frozen before analysis. Eight organochlorine pesticides and metabolites were measured in serum through the use of automated liquid/liquid extraction and subsequent sample clean-up. Final determination of target analytes was performed by isotope dilution gas chromatography high-resolution mass spectrometry GC/IDHRMS. The analytical method is described in Jones et al, 2012, which is a modification of the method described by Sjodin et al., 2004.

Refer to the Laboratory Method Files for a detailed description of the laboratory methods used.

There were no changes to the lab method, lab equipment, or lab site for this component in the NHANES 2009-2010 cycle.

Laboratory Method Files

Polybrominated diphenyl ethers (PBDEs), Polybrominated Biphenyls (PBBs), Polychlorinated biphenyls and Persistent Pesticides (September 2017)

Laboratory Quality Assurance and Monitoring

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

Detailed instructions on specimen collection and processing are discussed in the NHANES Laboratory Procedure Manual (LPM). Vials are stored under appropriate frozen (-30oC) conditions until they are shipped to the 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 competency assessment evaluation during visits to evaluate both the quality of the laboratory work and the quality-control procedures. Each laboratory staff member is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff member. 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 during “dry run” sessions. In addition, contract laboratories randomly perform repeat testing on 2% of all specimens.

NCHS developed and distributed a quality control protocol for all CDC and contract laboratories, which outlined the use of Westgard rules (Westgard, et al. 1981) 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 Environmental Health 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.

Analytic Notes

Refer to the 2009-2010 Laboratory Data Overview for general information on NHANES laboratory data.

Subsample Weights

Organochlorine pesticides were measured in a one-third subsample of participants 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.

Samples were pooled in groups of 8 samples per pool within 40 demographic groups. The analysis of NHANES 2009-2010 pooled-sample data must be conducted with the basic demographic variables provided in this data file. This pooled-sample data file cannot be linked to other NHANES 2009-2010 data. Because each sample person does not have an equal probability of selection, sample weighting is needed to produce correct population estimates of means, percentiles, and other descriptive statistics.

The pooled-sample weights required to produce estimates from these data are included in this data file. The analysis of pooled-samples from survey data is a relatively new field of study, and there is currently no established method to produce design effect adjusted variance estimates for these pooled results. These data cannot be analyzed using software designed for complex surveys because design features are not available.

Rationale and Methods Used to Create Pooled Results

The Centers for Disease Control and Prevention (CDC) provides an ongoing assessment of the US population's exposure to environmental chemicals by using biomonitoring in conjunction with CDC's National Health and Nutrition Examination Survey (NHANES). Characterizing the distributions of concentrations of environmental compounds or their metabolites in the US population is a primary objective of CDC's biomonitoring program. Historically, this characterization has been based on individual measurements of these compounds in body fluid or tissue from representative samples of the population. Pooling samples allows for larger sample volumes which can result in lower limits of detection and reduces the number of measurements and costs. In NHANES 2009-2010, a weighted pooled-sample design was implemented to facilitate pooling samples before making analytical measurements. Table 1 lists the International Union of Pure and Applied Chemistry (IUPAC) names, common abbreviation, and NHANES variable name for the analytes included in this data file.

Pools were prepared from serum collected from a random one-third subset of the NHANES 2009-2010 participants aged 12 years and older. Samples were pooled based on gender, race and Hispanic origin, and age. To implement the pooled-sample design, each participant sample was identified as belonging to one of 40 demographic groups based on race and Hispanic origin (Mexican American: MA, Other Hispanic: OH, non-Hispanic white: NHW, non-Hispanic black: NHB, Other race including multiracial: OTHER), gender (Male, Female), and age group (12-19, 20-39, 40-59, and 60+ years of age and older). Eight (8) samples were included in each pool. The number of pools created for each of the 40 demographic groups varied depending on the total number of individual samples available in a demographic group. The one-third subset of NHANES 2009-2010 represents 2524 individual samples, but because the pooled-sample design requires that all samples be of sufficient volume and that there be the same number of samples in each pool, 2322 samples were available to create 301 pools with 8 samples per pool (Exceptions are in Table 2). The variable SAMPLEID denotes the identification number for each pool and ranges from 1 through 303, excluding the numbers 265 and 266. Please refer to the Pooled-Sample Technical Support file (POOLTF_F) for detailed information on individual participants included in each pool.

In order to incorporate sample weighting into the pooled-sample design it was necessary to use a different volume of material from each sample contributing to a pool. The volume chosen for each sample in a pool was based on the ratio of its sampling weight to the sum of the sampling weights of all samples in the pool. To physically accomplish the pooling in the laboratory required that the ratio of the largest to the smallest sampling weight of samples in the same pool be no larger than about 4 or 5. The individual samples were sorted/stratified by sampling weight within each of the 40 demographic groups and pools were formed using samples with sampling weights adjacent to one another in the sorted list. The number of samples in the one-third subset, 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 2. Once the pools were created, summed sampling weights were further adjusted to account for the unused samples. These adjusted summed sampling weights are represented by the variable named WTSMSMPA.

Detection Limits

In the dataset, the whole-weight detection limit (pg/g serum) is a variable and dependent on the available sample size; however, the variation in sample size was low. Lipid adjusted detection limits are variable (ng/g lipid) due to differences of the lipid levels measured in individual pools/specimens. 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 2.

Table 1. NHANES Variable name, common abbreviation and International Union of Pure and Applied Chemistry (IUPAC) name for each analyte reported. Maximum limit of detection (MLOD) expressed as pg/serum and ng/g lipid).

Variable Name Common Abbrev. IUPAC Name Max LOD (pg/g serum) Max LOD (ng/g lipid)
LBCHCB HCB Hexachlorobenzene 13.4 3.11
LBCBHC B-HCCH BETA-Hexachlorocyclohexane 9.2 2.19
LBCGHC G-HCCH GAMA-Hexachlorocyclohexane (Lindane) 9.2 2.19
LBCOXY OXYCHLOR Oxychlordane 60.1 14.14
LBCTNA T-NONA Trans-Nonachlor 9.2 2.19
LBCPDE PP-DDE 2,2-Bis(4-chlorophenyl)-1,1-dichloroethene 15.6 3.68
LBCPDT PP-DDT 2,2-Bis(4-chlorophenyl-1,1,1-trichloroethan 9.2 2.19
LBCMIR MIREX Mirex 9.2 2.19

 

Table 2.  Number of subjects in the one-third subsample, number of individual serum samples available, number of usable samples, and number of pools formed from NHANES 2009-2010 participants per demographic group.

 

 

 

Race/ Ethnicity

 

 

 

Gender

 

Number of subjects in the one-third subsample/

Number of Samples Available/Number of Usable Samples

(Number of Pools)

12–19 years

(RIDAGEYR=1)1

20–39 years

(RIDAGEYR=2)

40–59 years

(RIDAGEYR=3)

60+ years

(RIDAGEYR=4)

Mexican

American

(RIDRETH1=1) 1

Male

(RIAGENDR=1) 1

65/61/602

(8)

67/65/64

(8)

70/65/64

(8)

43/40/40

(5)

Female

(RIAGENDR=2)

57/52/523

(7)

80/76/764

(10)

73/72/72

(9)

51/49/48

(6)

Other Hispanics

(RIDRETH1=2)

Male

(RIAGENDR=1)

22/20/205

(3)

35/34/346

(5)

40/39/397

(5)

26/24/24

(3)

Female

(RIAGENDR=2)

22/20/205

(3)

38/33/32

(4)

39/34/348

(5)

38/35/359

(5)

Non-Hispanic White

(RIDRETH1=3)

Male

(RIAGENDR=1)

91/79/7910

(10)

139/135/13511

(17)

146/142/136

(17)

182/175/168

(21)

Female

(RIAGENDR=2)

76/65/6312

(8)

164/151/15013

(19)

149/138/136

(17)

188/178/176

(22)

 

Non-Hispanic Black

(RIDRETH1=4)

Male

(RIAGENDR=1)

45/43/4314

(6)

56/52/523

(7)

60/54/5415

(7)

72/67/6716

(9)

Female

(RIAGENDR=2)

53/48/48

(6)

63/57/56

(7)

60/53/5317

(7)

58/52/523

(7)

Other Race  including  Multiracial

(RIDRETH1=5)

Male

(RIAGENDR=1)

13/11/1118

(2)

21/19/1819

(3)

18/18/16

(2)

16/15/1520

(2)

Female

(RIAGENDR=2)

18/17/16

(2)

31/30/3021

(4)

23/21/2122

(3)

16/15/1323

(2)

1 Value of this categorical variable in the data set
2 60 Usable samples: seven 8 sample and one 4 sample pool were created
3 52 Usable samples: six 8 sample and one 4 sample pool
4 76 Usable samples: nine 8 sample and one 4 sample pool
5 20 Usable samples: two 8 sample and one 4 sample pool
6 34 Usable samples: three 8 sample and two 5 sample pools
7 39 Usable samples: four 8 sample and one 7 sample pool
8 34 Usable samples: four 8 sample and one 2 sample pool
9 35 Usable samples: four 8 sample and one 3 sample pool
10 79 Usable samples: nine 8 sample and one 7 sample pool
11 135 Usable samples: sixteen 8 sample and one 7 sample pool
12 63 Usable samples: seven 8 sample and one 7 sample pool
13 150 Usable samples: eighteen 8 sample and one 6 sample pool
14 34 Usable samples: five 8 sample and one 3 sample pool
15 54 Usable samples: six 8 sample and one 6 sample pool
16 67 Usable samples: eight 8 sample and one 3 sample pool
17 53 Usable samples: six 8 sample and one 5 sample pool
18 11 Usable samples: one 6 sample and one 5 sample pool
19 18 Usable samples: one 8 sample, one 6 sample, and one 4 sample pool
20 15 Usable samples: one 8 sample and one 7 sample pool
21 30 Usable samples: three 8 sample and one 6 sample pool
22 21 Usable samples: two 8 sample and one 5 sample pool
23 13 usable samples: one 8 sample and one 5 sample pool.

Methodological approaches for analysis

There are a few pooled-sample methodological publications which address approaches related to the following topics:

• Variance estimation and bias correction when pooling samples from log-normally distributed populations (Caudill, 2010a; Caudill, 2010b; Caudill et al., 2007; Li et al., 2014);

• Models that incorporate measurement error when analyzing pooled-samples from normally or log-normally distributed populations (Caudill, 2010a);

• Incorporation of sample weighting into a pooled-sample design (Caudill, 2012; Caudill, 2010a);

• Estimation of standard errors and confidence limits for point estimates from pooled-samples (Caudill, 2012; Caudill, 2010a).

References

Codebook and Frequencies

SAMPLEID - Pool identification number

Variable Name:
SAMPLEID
SAS Label:
Pool identification number
English Text:
Pool identification number
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 to 303 Range of Values 301 301
. Missing 0 301

RIDRETH1 - Race/Hispanic origin

Variable Name:
RIDRETH1
SAS Label:
Race/Hispanic origin
English Text:
Recode of reported race and Hispanic origin information
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Mexican American 61 61
2 Other Hispanic 33 94
3 Non-Hispanic White 131 225
4 Non-Hispanic Black 56 281
5 Other Race, Including Multiracial 20 301
. Missing 0 301

RIDAGGRP - Age group

Variable Name:
RIDAGGRP
SAS Label:
Age group
English Text:
Age group
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 12-19 years 55 55
2 20-39 years 84 139
3 40-59 years 80 219
4 60+ years 82 301
. Missing 0 301

RIAGENDR - Gender

Variable Name:
RIAGENDR
SAS Label:
Gender
English Text:
Gender
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Male 148 148
2 Female 153 301
. Missing 0 301

RIANSMP - Number of samples in a pool

Variable Name:
RIANSMP
SAS Label:
Number of samples in a pool
English Text:
Number of samples in a pool
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
2 to 8 Range of Values 301 301
. Missing 0 301

WTSMSMPA - Sum of adjusted subsample weights

Variable Name:
WTSMSMPA
SAS Label:
Sum of adjusted subsample weights
English Text:
Adjust sum sampling weights in same pool
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
49070.542891 to 2980185.9468 Range of Values 301 301
. Missing 0 301

LBCBHC - Beta-hexachlorocyclohexane (pg/g)

Variable Name:
LBCBHC
SAS Label:
Beta-hexachlorocyclohexane (pg/g)
English Text:
Beta-hexachlorocyclohexane (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.465 to 4801 Range of Values 295 295
. Missing 6 301

LBCBHCLA - B-hexachlorocyclohexane Lipid Adj (ng/g)

Variable Name:
LBCBHCLA
SAS Label:
B-hexachlorocyclohexane Lipid Adj (ng/g)
English Text:
Beta-hexachlorocyclohexane Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.5657 to 899.5 Range of Values 295 295
. Missing 6 301

LBDBHCLC - Beta-hexachlorocyclohexane comment code

Variable Name:
LBDBHCLC
SAS Label:
Beta-hexachlorocyclohexane comment code
English Text:
Beta-hexachlorocyclohexane comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 260 260
1 Below lower detection limit 35 295
. Missing 6 301

LBCGHC - Gamma-hexachlorocyclohexane (pg/g)

Variable Name:
LBCGHC
SAS Label:
Gamma-hexachlorocyclohexane (pg/g)
English Text:
Gamma-hexachlorocyclohexane (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.465 to 9.192 Range of Values 301 301
. Missing 0 301

LBCGHCLA - G-hexachlorocyclohexane Lipid Adj (ng/g)

Variable Name:
LBCGHCLA
SAS Label:
G-hexachlorocyclohexane Lipid Adj (ng/g)
English Text:
Gamma-hexachlorocyclohexane Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3748 to 2.192 Range of Values 301 301
. Missing 0 301

LBDGHCLC - Gamma-hexachlorocyclohexane comment code

Variable Name:
LBDGHCLC
SAS Label:
Gamma-hexachlorocyclohexane comment code
English Text:
Gamma-hexachlorocyclohexane comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 1 1
1 Below lower detection limit 300 301
. Missing 0 301

LBCHCB - Hexachlorobenzene (pg/g)

Variable Name:
LBCHCB
SAS Label:
Hexachlorobenzene (pg/g)
English Text:
Hexachlorobenzene (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
20.16 to 1351 Range of Values 301 301
. Missing 0 301

LBCHCBLA - Hexachlorobenzene Lipid Adj (ng/g)

Variable Name:
LBCHCBLA
SAS Label:
Hexachlorobenzene Lipid Adj (ng/g)
English Text:
Hexachlorobenzene Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
4.573 to 192.4 Range of Values 301 301
. Missing 0 301

LBDHCBLC - Hexachlorobenzene comment code

Variable Name:
LBDHCBLC
SAS Label:
Hexachlorobenzene comment code
English Text:
Hexachlorobenzene comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 301 301
1 Below lower detection limit 0 301
. Missing 0 301

LBCMIR - Mirex (pg/g)

Variable Name:
LBCMIR
SAS Label:
Mirex (pg/g)
English Text:
Mirex (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.465 to 224.1 Range of Values 301 301
. Missing 0 301

LBCMIRLA - Mirex Lipid Adj (ng/g)

Variable Name:
LBCMIRLA
SAS Label:
Mirex Lipid Adj (ng/g)
English Text:
Mirex Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.495 to 40.08 Range of Values 301 301
. Missing 0 301

LBDMIRLC - Mirex comment code

Variable Name:
LBDMIRLC
SAS Label:
Mirex comment code
English Text:
Mirex comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 198 198
1 Below lower detection limit 103 301
. Missing 0 301

LBCOXY - Oxychlordane (pg/g)

Variable Name:
LBCOXY
SAS Label:
Oxychlordane (pg/g)
English Text:
Oxychlordane (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
22.63 to 303.5 Range of Values 296 296
. Missing 5 301

LBCOXYLA - Oxychlordane Lipid Adj (ng/g)

Variable Name:
LBCOXYLA
SAS Label:
Oxychlordane Lipid Adj (ng/g)
English Text:
Oxychlordane Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.394 to 57.13 Range of Values 296 296
. Missing 5 301

LBDOXYLC - Oxychlordane comment code

Variable Name:
LBDOXYLC
SAS Label:
Oxychlordane comment code
English Text:
Oxychlordane comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 176 176
1 Below lower detection limit 120 296
. Missing 5 301

LBCPDE - p,p'-DDE (pg/g)

Variable Name:
LBCPDE
SAS Label:
p,p'-DDE (pg/g)
English Text:
p,p'-dichlorodiphenyltrichloroethene (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
131.9 to 54740 Range of Values 299 299
. Missing 2 301

LBCPDELA - p,p'-DDE Lipid Adj (ng/g)

Variable Name:
LBCPDELA
SAS Label:
p,p'-DDE Lipid Adj (ng/g)
English Text:
p,p'-dichlorodiphenyltrichloroethene Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
26.21 to 7134 Range of Values 299 299
. Missing 2 301

LBDPDELC - p,p'-DDE comment code

Variable Name:
LBDPDELC
SAS Label:
p,p'-DDE comment code
English Text:
p,p'-dichlorodiphenyltrichloroethene comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 299 299
1 Below lower detection limit 0 299
. Missing 2 301

LBCPDT - p,p'-DDT (pg/g)

Variable Name:
LBCPDT
SAS Label:
p,p'-DDT (pg/g)
English Text:
p,p'-dichlorodiphenyltrichlorethane (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.465 to 4437 Range of Values 301 301
. Missing 0 301

LBCPDTLA - p,p'-DDT Lipid Adj (ng/g)

Variable Name:
LBCPDTLA
SAS Label:
p,p'-DDT Lipid Adj (ng/g)
English Text:
p,p'-dichlorodiphenyltrichlorethane Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.7071 to 578.2 Range of Values 301 301
. Missing 0 301

LBDPDTLC - p,p'-DDT comment code

Variable Name:
LBDPDTLC
SAS Label:
p,p'-DDT comment code
English Text:
p,p'-dichlorodiphenyltrichlorethane comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 290 290
1 Below lower detection limit 11 301
. Missing 0 301

LBCTNA - trans-Nonachlor (pg/g)

Variable Name:
LBCTNA
SAS Label:
trans-Nonachlor (pg/g)
English Text:
trans-Nonachlor (pg/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
6.787 to 653.1 Range of Values 299 299
. Missing 2 301

LBCTNALA - trans-Nonachlor Lipid Adj (ng/g)

Variable Name:
LBCTNALA
SAS Label:
trans-Nonachlor Lipid Adj (ng/g)
English Text:
trans-Nonachlor Lipid Adjusted (ng/g)
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1.556 to 112.5 Range of Values 299 299
. Missing 2 301

LBDTNALC - trans-Nonachlor comment code

Variable Name:
LBDTNALC
SAS Label:
trans-Nonachlor comment code
English Text:
trans-Nonachlor comment code
Target:
Both males and females 12 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 298 298
1 Below lower detection limit 1 299
. Missing 2 301