• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Data Processing and Editing
• Laboratory Quality Assurance and Monitoring
• Analytic Notes
• Codebook
  • SEQN - Respondent sequence number
  • WTSA2YR - Environmental A 2 year weights
  • URXUP8 - Urinary perchlorate (ng/mL)
  • URDUP8LC - Urinary perchlorate comment code
  • URXNO3 - Urinary nitrate (ng/mL)
  • URDNO3LC - Urinary nitrate comment code
  • URXSCN - Urinary thiocyanate (ng/mL)
  • URDSCNLC - Urinary thiocyanate comment code
  • URXUCR - Urinary creatinine (mg/dL)

National Health and Nutrition Examination Survey

2009-2010 Data Documentation, Codebook, and Frequencies

Perchlorate, Nitrate & Thiocyanate - Urine (PERNT_F)

Data File: PERNT_F.xpt

First Published: April 2014

Last Revised: NA

Component Description

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 methemeglobinemia, 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 US.

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.

Eligible Sample

Participants aged 6 years and older, who are eligible for the one_third subsample, were tested.

Description of Laboratory Methodology

Perchlorate, Urinary Nitrate, and Thiocyanate: 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.

Data Processing and Editing

Urine specimens from urinary perchlorate, nitrate, and thiocyanate were processed, stored, and shipped to the Division of Environmental Health 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 LPM. Vials are stored under appropriate frozen (–20°C) conditions until they are shipped to National Center for Environmental Health for testing.

Detailed instructions on specimen collection and processing can be found on the NHANES website.

Laboratory Quality Assurance and Monitoring

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/Medical Technologists Procedures Manual (LPM). Read the LABDOC file for detailed QA/QC protocols.

A detailed description of the quality assurance and quality control procedures can be found on the NHANES website.

Analytic Notes

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

Subsample Weights

Data for Urinary perchloriate, thiocyanate and nitrate were obtained in a 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.”

Variance Estimation

The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The NHANES Demographic Data File contains demographic and 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.

Links to NHANES Data Files

This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier SEQN.

Detection Limits

The lower detection limits were 700 ng/mL for urinary nitrate, and 20 ng/mL for urinary thiocyanate.

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 two.

Two variables are provided for each of these analytes. The variable named URD___LC indicates whether the result was below the limit of detection. There are two values: “0” and “1””. “0” means 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 named URX___ provides the analytic result for that 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.

 

Codebook and Frequencies