National Health and Nutrition Examination Survey

NOTE: Four additional perfluoroalkyl and polyfluoroalkyl substances (PFAS), namely four isomers of PFOA and PFOS, were measured using surplus serum specimens from NHANES 2013-2014. These isomers data should be used in conjunction with this dataset (PFAS_H), and can be found in the Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) – Linear and Branched PFOS and PFOA Isomers (SSPFAS_H) dataset on this website. Starting with NHANES 2015-2016, these isomers will be included with the perfluoroalkyl and polyfluoroalkyl substances (PFAS) dataset.

You may also use the link below to access the dataset for these isomers:

https://wwwn.cdc.gov/nchs/nhanes/2013-2014/sspfas_h.xpt

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are used in multiple commercial applications including surfactants, lubricants, paints, polishes, food packaging and fire-retarding foams. Certain PFAS are used in the manufacture of polymers used in many industrial and consumer products, including soil, stain, grease, and water resistant coatings on textiles and carpet; uses in the automotive, mechanical, aerospace, chemical, electrical, medical, and building/construction industries; personal care products; and non-stick coatings on cookware. Some PFASs are ubiquitous contaminants found both in humans and animals worldwide.

The calculated sum of isomers in the PFAS (formerly PFC) dataset for the 2013-2014 cycle is comparable to the total levels reported in previous cycles of NHANES.

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

Online-solid phase extraction coupled to High Performance Liquid Chromatography-Turbo Ion Spray ionization-tandem Mass Spectrometry (online SPE-HPLC-TIS-MS/MS) is used for the quantitative detection of PFAS including 2-(N-methyl-perfluorooctane sulfonamido) acetic acid (Me-PFOSA-AcOH), perfluorobutane sulfonate (PFBuS), perfluorohexane sulfonate (PFHxS), perfluoroheptanoate (PFHpA), perfluorononanoate (PFNA), perfluorodecanoate (PFDeA), perfluoroundecanoate (PFUA), and perfluorododecanoate (PFDoA). Briefly, after dilution with formic acid, one aliquot of 100 μL of serum is injected into a commercial column switching system allowing for concentration and chromatographic separation of the analytes. Detection and quantification are done using tandem mass spectrometry (Kuklenyik Z, et al. 2005).

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

They were no changes to the lab equipment or lab site for this component in the NHANES 2013-2014 cycle. However, the lab method was changed to include both linear and branched isomers of PFOS and PFOA. These isomers data can be found in the Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) – Linear and Branched PFOS and PFOA Isomers (SSPFAS_H) dataset on this website.

Perfluoroalkyl and Polyfluoroalkyl Substances (July 2016)

Serum specimens are 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 Procedures Manual (LPM). Vials are stored under appropriate frozen (–20°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 Laboratory Procedures Manual (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 Science’s quality control and quality assurance performance criteria for accuracy and precision, similar to specifications outlined by Westgard (Westgard et al, 1981; 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

Serum PFAS were measured in a one third subsample of persons 12 years and over. 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 2013-2014 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.

The 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 “L” (ex., LBDPFHSL) 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., LBDPFHSL=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 LBX (ex., LBXPFHS) provides the analytic result for that analyte.

The lower limit of detection (LLOD, in ng/mL) for each PFAS is:

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.