• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Laboratory Method Files
• Laboratory Quality Assurance and Monitoring
• Data Processing and Editing
• Analytic Notes
• References
• Codebook
  • SEQN - Respondent sequence number
  • UR2UCSTS - Urine collection status
  • UR2UP8 - Perchlorate, urine - 2nd Collect (ng/mL)
  • UR2NO3 - Nitrate, urine - 2nd Collection (ng/mL)
  • URDNO2LC - Nitrate - 2nd Collection Comt Code
  • UR2SCN - Thiocyanate, urine - 2nd Collect (ng/mL)
  • UR2CR - Creatinine, urine 2nd Collection (mg/dL)
  • VPSU - Variance PSU
  • VSTRA - Variance stratum
  • WT1YUR - 1 year urine weight
  • WT1YUR01 - 1 year urine weight - Jackknife 01
  • WT1YUR02 - 1 year urine weight - Jackknife 02
  • WT1YUR03 - 1 year urine weight - Jackknife 03
  • WT1YUR04 - 1 year urine weight - Jackknife 04
  • WT1YUR05 - 1 year urine weight - Jackknife 05
  • WT1YUR06 - 1 year urine weight - Jackknife 06
  • WT1YUR07 - 1 year urine weight - Jackknife 07
  • WT1YUR08 - 1 year urine weight - Jackknife 08
  • WT1YUR09 - 1 year urine weight - Jackknife 09
  • WT1YUR10 - 1 year urine weight - Jackknife 10
  • WT1YUR11 - 1 year urine weight - Jackknife 11
  • WT1YUR12 - 1 year urine weight - Jackknife 12
  • WT1YUR13 - 1 year urine weight - Jackknife 13
  • WT1YUR14 - 1 year urine weight - Jackknife 14
  • WT1YUR15 - 1 year urine weight - Jackknife 15
  • VPSUBRR - Variance PSU for BRR
  • VSTRABRR - Variance stratum for BRR
  • WT1YUB01 - 1 year urine weight - Fay's BRR 01
  • WT1YUB02 - 1 year urine weight - Fay's BRR 02
  • WT1YUB03 - 1 year urine weight - Fay's BRR 03
  • WT1YUB04 - 1 year urine weight - Fay's BRR 04
  • WT1YUB05 - 1 year urine weight - Fay's BRR 05
  • WT1YUB06 - 1 year urine weight - Fay's BRR 06
  • WT1YUB07 - 1 year urine weight - Fay's BRR 07
  • WT1YUB08 - 1 year urine weight - Fay's BRR 08
  • WT1YUB09 - 1 year urine weight - Fay's BRR 09
  • WT1YUB10 - 1 year urine weight - Fay's BRR 10
  • WT1YUB11 - 1 year urine weight - Fay's BRR 11
  • WT1YUB12 - 1 year urine weight - Fay's BRR 12
  • WT1YUB13 - 1 year urine weight - Fay's BRR 13
  • WT1YUB14 - 1 year urine weight - Fay's BRR 14
  • WT1YUB15 - 1 year urine weight - Fay's BRR 15
  • WT1YUB16 - 1 year urine weight - Fay's BRR 16
• Appendix 1

National Health and Nutrition Examination Survey

2013-2014 Data Documentation, Codebook, and Frequencies

Perchlorate, Nitrate & Thiocyanate - 24-Hour Urine - Second Collection (U2PN_H_R)

RDC Only Data File: U2PN_H_R.xpt

First Published: July 2020

Last Revised: NA

Due to disclosure issues, this dataset is not available publicly. Access may be obtained through the NCHS Research Data Center (https://www.cdc.gov/rdc).

Component Description

The 24-Hour Urine Collection component was added to NHANES in 2014 to: 1) estimate dietary intakes of sodium and potassium; 2) estimate the excretion of microalbumin (albumin and creatinine); and 3) assess measures of kidney markers (phosphorus, magnesium, calcium, oxalate, and urea nitrogen), phytoestrogen, caffeine, volatile organic compounds, and iodine in the U.S. population.

In 2014, a random half sample of non-pregnant participants aged 20-69 years and examined in the mobile examination center (MEC) were asked to collect their urines for a 24-hour period. For the first half of the year, a random half of those who completed the initial 24-hour urine collection were recruited to collect a second 24-hour urine specimen 3 to 10 days later. For the second half of the year, all those who completed the first 24-hour urine collection were recruited to collect a second 24-hour urine specimen. Data processing information from the initial and second 24-hour urine collections was released in two separate datasets (U1_H_R and U2_H_R). Each of these two files contains information on the following: total urine volume, length of collection, completeness of the urine collection, number of complete urine specimens, collection day of the week, and responses to questions on the participants’ experience collecting the urine to assess completeness of the specimen. Please see the documentation for these two files for more details.

Separate datasets were produced to include laboratory results of analytes from the 24-hour urine collections. The present file contains analyte data for urinary perchlorate, nitrate & thiocyanate. See Appendix I for the list of data files for the 24-hour urine collection.

Urinary Perchlorate

Perchlorate has been used as an oxidant in solid fuel propellants for rockets and missiles since the 1950s. Lesser amounts of perchlorate are used in matches and fireworks. Perchlorate can also form naturally in the environment and can accumulate in nitrate-rich mineral deposits mined for use in fertilizers. Drinking water, milk, and certain plants with high water content (e.g., lettuce) can be the main sources of perchlorate intake for humans. Perchlorate has been used medically to treat hyperthyroidism. Its inhibitory effect on thyroid hormone production has led to concerns that exposure even to low levels of perchlorate in the environment might affect vulnerable groups, such as pregnant women with inadequate iodine intake and infants for whom thyroid hormone levels must be maintained adequately for normal brain development. Perchlorate taken into the body is rapidly eliminated in the urine, within a matter of hours. Measurement of urinary perchlorate is useful to assess recent human exposure.

Urinary Nitrate and Thiocyanate

Nitrate and thiocyanate are polyatomic anions that can disrupt thyroid function by competitively inhibiting iodide uptake, similar to the action of perchlorate. Nitrate, thiocyanate, and perchlorate can reversibly bind to the sodium-iodide symporter (NIS) protein resulting in reduced iodine absorption by the thyroid. Nitrate, thiocyanate and perchlorate interact additively to impair iodide uptake by the thyroid. Therefore, assessment of the impact of perchlorate exposure on thyroid function should include assessment of nitrate and thiocyanate exposure. By assessing exposure to each of the three physiologically relevant NIS-inhibitors, the relative impact of each chemical on thyroid function can be estimated and appropriate regulatory action taken if exposures are negatively impacting thyroid hormone levels. Impaired thyroid function can lead to hypothyroidism, proliferative thyroid lesions, and impaired neurodevelopment in infants.

Nitrate poisoning can also lead to methemoglobinemia, primarily in infants. The prevalence of nitrate exposure is likely due to nitrate intake from both food and drinking water, with foods (e.g., vegetables, milk, dairy products) thought to account for the majority of nitrate intake for typical American adults. Nitrate anion can also form endogenously. Public health prevention efforts have reduced the prevalence of methemoglobinemia in the United States. A reference range for urinary nitrate will provide useful information relevant to nitrate poisoning and subclinical methemoglobinemia in the U.S.

Thiocyanate is also a biomarker of cyanide exposure from tobacco smoke or diet. Thiocyanate primarily forms in the body as a metabolite of cyanide from tobacco smoke or cyanogenic foods, such as cassava. Exposure to toxic levels of cyanide can result from numerous chemical reactions. Lower levels of thiocyanate can also be found in milk, dairy products, and some vegetables. Therefore, a defined reference range for thiocyanate will provide useful benchmark data in case of a cyanide exposure event.

To reduce the risk of inadvertent disclosure, all data from this 1-year 24-hour urine collection can only be accessed through the NCHS Research Data Center (RDC). Instructions for requesting use of these data are available from the RDC website (https://www.cdc.gov/rdc/).

Eligible Sample

The eligible sample was a random one-half sample of all examined participants aged 20-69 years with a few participants eliminated based on exclusion criteria (e.g., pregnant). For the first half of the year, a random half of those who completed the initial 24-hour urine collection were recruited to collect a second 24-hour urine specimen 3 to 10 days later. For the second half of the year, all those who completed the first 24-hour urine collection were recruited to collect a second 24-hour urine specimen.

Description of Laboratory Methodology

This method is a quantitative procedure for the measurement of nitrate, perchlorate, and thiocyanate in human urine using ion chromatography coupled with electrospray tandem mass spectrometry. Chromatographic separation is achieved using an IonPac AS16 column with sodium hydroxide as the eluent. The eluent from the column is ionized using an electrospray interface to generate and transmit negative ions into the mass spectrometer. Comparison of relative response factors (ratio of native analyte to stable isotope labeled internal standard) with known standard concentrations yields individual analyte concentrations.

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

This is a new component in the 2014 survey cycle.

Laboratory Method Files

Urinary Perchlorate, Nitrate, and Thiocyanate Laboratory Procedure Manual (July 2020)

Laboratory Quality Assurance and Monitoring

Urine 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 24-Hour Urine Study Procedures Manual. Vials were stored under appropriate frozen (-30°C) conditions until they were 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 Laboratory Procedures Manual (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 QC 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 QC 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 Laboratory Sciences’ QA/QC 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

Variables with data from 24-hour urine first collection and second collection specimens are denoted with a “UR1” and “UR2” prefix, respectively.

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

There are over 800 laboratory tests performed on NHANES participants. However, not all participants provided biospecimens or enough volume for all the tests to be performed. The specimen availability can also vary by age or other population characteristics. Analysts should evaluate the extent of missing data in the dataset related to the outcome of interest as well as any predictor variables used in the analyses to determine whether additional re-weighting for item non-response is necessary.

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

NHANES participants were selected on the basis of a national probability design. In order to increase the number of participants for specific demographic groups, a multi-stage, unequal probability of selection design was implemented. In 2014, the sample design included an oversample of certain demographic groups: persons 80 years and older, non-Hispanic black, non-Hispanic Asian, Hispanic, and low income white and other persons. Sample weights are constructed that encompass the unequal probabilities of selection, as well as adjustments for non-participation by selected sample persons. In order to produce national, representative estimates, the appropriate sample weights must be used.

The 24-hour urine collection was conducted in a random one-half subsample of 1,103 persons 20-69 years examined in the mobile examination center in 2014. A special one-year urine sample weight (WT1YUR) is provided for the 827 participants who provided a complete 24-hour urine specimen to obtain representative national estimates based on this first 24-hour urine collection. As with other NHANES subsamples, the 24-hour urine sample weights account for the additional probability of selection into the subsample component as well as the additional nonresponse. This sample weight, along with strata (VSTRA) and PSUs (VPSU) are used to calculate variance estimates based on the Taylor Series Linearization method. In addition, 16 Fay-adjusted balanced repeated replication (Fay’s BRR) weights (WT1YUB01 – WT1YUB16), along with their corresponding strata (VSTRABRR) and PSUs (VPSUBRR), and 15 Jackknife replicate weights (WT1YUR01 – WT1YUR15) that can be used with VSTRA and VPSU are included in the files to obtain variance estimates based on a replication method. The Fay’s BRR weights were created with an adjustment factor of 0.3. There is no separate sample weight provided for use with the data collected for the second 24-hour urine specimen. These data were collected for the purpose of estimating within-person variability and not for obtaining nationally representative estimates based on the second 24-hour urine sample. New sample weights would need to be calculated by the user if any additional analytical efforts were planned for the second collection 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 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.

Please see Appendix 1 for the list of data files produced from the 24-hour urine collection.

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 “1LC” (ex., URDUP8LC) 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., URDUP8LC=1), an imputed fill value was placed in the analyte results field. This value is the lower limit of detection divided by the square root of 2 (LLOD/sqrt[2]). The other variable prefixed UR2 (ex., UR2UP8) provides the analytic result for that analyte.

The lower limit of detection (LLOD in ng/mL) for 24-Hour Urinary Perchlorate, Nitrate, and Thiocyanate –First and Second Collections:

References

• Caudill, S.P., Schleicher, R.L., Pirkle, J.L. Multi-rule quality control for the age-related eye disease study. Statist. Med. (2008) 27(20):4094-40106.
• Westgard J.O., Barry P.L., Hunt M.R., Groth T. A multi-rule Shewhart chart for quality control in clinical chemistry. Clin Chem (1981) 27:493-501.

Codebook and Frequencies