Ethylene Oxide
Ethylene oxide (EO) is an industrial chemical used to manufacture consumer and non-consumer products and is used as a gaseous sterilant for medical devices. EO has been classified as a human carcinogen (Group 1) by the International Agency for Research on Cancer (IARC). EO has been detected in tobacco smoke, automobile exhaust, and some foods (Clin Chem, 2016). EO is formed endogenously in animals and humans from Cytochrome P450 2E1 (CYP2E1) mediated metabolic oxidation of ethylene. It is also formed in vivo during normal physiological processes, such as methionine oxidation, lipid peroxidation, and during metabolic activity of intestinal bacteria. Information on endogenous and exogenous EO exposure in the general population is very limited and is needed to assess potential health effects associated with this exposure and to monitor changes in exposure over time.
Examined participants aged 6 years and older from a one-third subsample were eligible.
This procedure describes a method based on the modified Edman reaction to measure hemoglobin adducts of EO in human whole blood or erythrocytes. Specifically, the reaction products with the N-terminal valine residue of the hemoglobin protein chains (N-[2-carbamoyl ethyl] valine and N-[2-hydroxycarbamoyl-ethyl] valine EO adducts) are measured.
The modified Edman reaction uses the effect of N-alkylated amino acids to form Edman products in neutral or alkaline conditions versus in acidic conditions required in conventional Edman reaction procedures. It was first described for N-terminal hemoglobin adducts of EO, propylene oxide, and styrene oxide and later optimized to increase yield of Edman products of these adducts. This optimized method was further refined and modified in-house to increase sensitivity and enable automation.
The procedure described here consists of 4 parts:
The measurement is achieved using a commercial assay kit based on a well-established procedure commonly used in clinical chemistry. Quantitation of hemoglobin adducts of EO is performed using octapeptides with the same amino acid sequence as the N-terminal of the beta-chain of hemoglobin with EO attached at the valine residue.
Refer to the Laboratory Method Files section for a detailed description of the laboratory method used.
There were no changes to the lab method, lab equipment, or lab site for this component in the NHANES 2015-2016 cycle.
Acrylamide and Glycidamide Lab Procedure Manual (December 2019)
Washed-packed red blood cell specimens 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 specimen collection and processing instructions are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials are stored under appropriate frozen (–30°C) conditions until they are shipped to National Center for Environmental Health for testing.
The NHANES quality assurance and quality control protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Amendments mandates. Detailed quality control and quality assurance 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 MEC 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, and testing procedures. Each member is observed and given constructive feedback. 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 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 QC protocol for all the contract laboratories, which outlined the use of Westgard rules (Westgard et al, 1981) when testing NHANES specimens. Progress reports describing 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’ QA/QC performance criteria for accuracy and precision, similar to the Westgard rules (Caudill et al, 2008).
The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.
Refer to the 2015-2016 Laboratory Data Overview for general information on NHANES laboratory data.
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.
Subsample Weights
Hemoglobin adducts of EO were measured in a one-third subsample of participants 6 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.
Demographic and Other Related Variables
The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2015-2016 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the 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.
The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture.
This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).
Detection Limits
The detection limits were constant for all analytes in the data set. Two variables are provided for each of these analytes. The variable name ending with “LC” (ex., LBDEOALC) indicates whether the result was below the limit of detection: the value “0” indicates 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 prefixed LBX (ex., LBXEOA) provides the analytic result for that analyte. For analytes with results below the lower limit of detection (ex., LBDEOALC =1), an imputed value was provided. This value is the lower limit of detection divided by the square root of 2 (LLOD/sqrt[2]).
The lower limit of detection (LLOD, in pmol/g Hb) for EO is:
|
Variable Name |
Analyte Description |
LLOD1 |
|
LBXEOA |
Hemoglobin adducts of EO |
8.20 |
1 LLOD was adjusted for a calibrator bias, see section below for details.
Bias adjustments Applied to Hemoglobin Adducts of Ethylene Oxide (LBXEOA)
A systematic bias was discovered for the measurement of hemoglobin adducts of EO in red blood cells in the NHANES 2013 - 2014 and 2015 – 2016 cycles. The bias was detected after a new batch of calibrators were used after LBXEOA measurements were completed. The calibrators were obtained from a commercial source. Further investigations conducted by the CDC testing laboratory confirmed that the initial calibrator materials did not have the purity specified by the manufacturer. This discrepancy between the anticipated concentration of the calibrators and the actual concentration led to systematic bias in LBXEOA results. The systematic nature of these biases permitted retrospective adjustment through an algebraic correction using a formula.
The lower limit of detection (LLOD) and the measurement values for LBXEOA were initially adjusted in April 2022 and the revised data file released that same month. The formula used to adjust measurements required logarithmic transformation. However, the formula was applied to data that were not uniformly log-transformed, rendering the revised measurement values released in April 2022 invalid.
In May 2023, the LLOD and the measurement values for LBXEOA were correctly adjusted using the following formula , which is based on log-transformed measurement values:
LBXEOA = 0.58026 (LBXEOA_original 1.03562)
1The derivation of the formula is as follows:
log10[LBXEOA] = log10 (LBXEOA_original *1.03562-0.23638)
LBXEOA = 10 log10(LBXEOA_original *1.03562-0.23638)
LBXEOA = 0.58026 (LBXEOA_original 1.03562)
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 16357.767797 to 708844.24678 | Range of Values | 2644 | 2644 | |
| 0 | No Lab Result | 48 | 2692 | |
| . | Missing | 0 | 2692 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 5.8 to 1113.8 | Range of Values | 2375 | 2375 | |
| . | Missing | 317 | 2692 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 0 | detectable result | 2342 | 2342 | |
| 1 | below detectable limit | 33 | 2375 | |
| . | Missing | 317 | 2692 |