National Health and Nutrition Examination Survey

Polycyclic Aromatic Hydrocarbons (PAHs)

PAHs constitute a group of chemicals formed during the incomplete combustion of coal, oil and gas, garbage, and other organic substances. In general, people are exposed to mixtures of PAHs, and the sources are widespread, including vehicle exhaust, asphalt, coal tar, wild fires, agricultural burning, charbroiled foods, and tobacco smoke. Upon entering the body, PAHs are readily metabolized and eliminated in urine. Urinary concentrations of PAH metabolites, specifically monohydroxylated PAHs (OH-PAHs), have been used as biomarkers of human exposure to select PAHs including naphthalene, fluorene, phenanthrene, and pyrene.

Examined participants aged 6 years and older from a one-third sample were eligible.

The specific analytes measured in this method are monohydroxylated metabolites of PAHs (OH-PAHs), namely 1-hydroxynaphthalene, 2-hydroxynaphthalene, 2-hydroxyfluorene, 3-hydroxyfluorene, 1-hydroxyphenanthrene, 2- & 3-hydroxyphenanthrene, and 1-hydroxypyrene. The analytical procedure involves enzymatic hydrolysis of glucuronidated/sulfated OH-PAH metabolites in urine, extraction by on-line solid phase extraction, and separation and quantification using isotope dilution high performance liquid chromatography-tandem mass spectrometry (on-line SPE-HPLC-MS/MS) (Wang et al., 2016).

Refer to the Laboratory Method Files section for detailed description of the laboratory procedure manual of the method used.

In previous cycles, the method used for the quantification of OH-PAHs was based on derivatization and gas chromatography-tandem mass spectrometry. Starting with the current NHANES cycle, we used a different approach that relies on liquid chromatography-tandem mass spectrometry. Note that with the on-line SPE-HPLC-MS/MS approach, the combined levels of 2- & 3-hydroxyphenanthrene in NHANES 2013-2014 are comparable to the sum of urinary levels of 2-hydroxyphenanthrene and 3-hydroxyphenanthrene reported as two separate variables in previous NHANES cycles. There were no changes to the lab site for this component in the NHANES 2013-2014 cycle.

Eight monohydroxy-polycyclic aromatic hydrocarbons (December 2016)

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

Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials are stored frozen (–20°C) 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 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.

NCEH developed and distributed a quality control protocol for all the 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 by NCHS 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).

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

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

Subsample Weights

Urinary OH-PAHs were measured in a one third subsample of persons 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 Demographic (Demographic Data) 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.

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 of the analytes in the data set. Two variables are provided for each of these analytes. The variable name ending in “LC” (ex., URDP04LC) indicates whether the result was below the limit of detection: The value “0” means that the result was at or above the limit of detection, “1” indicates that the result was below the limit of detection. For analytes with analytic results below the lower limit of detection (ex., URDP04LC=1), an imputed fill value was placed in the analyte results field. This value is the lower limit of detection divided by square root of 2 (LLOD/sqrt [2]). The other variable prefixed URX (ex., URXP04) provides the analytic result for the analyte.

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.

* URXP25 values are comparable to the sum of urinary levels of 2-hydroxyphenanthrene and 3-hydroxyphenanthrene reported as two separate variables (URXP07 and URXP05, respectively) in previous NHANES cycles.