• 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
  • WTSA2YR - Subsample A weights
  • URXUCM - Chromium, Urine (ug/L)
  • URDUCMLC - Chromium, Urine Comment Code

National Health and Nutrition Examination Survey

2017-2018 Data Documentation, Codebook, and Frequencies

Chromium - Urine (UCM_J)

Data File: UCM_J.xpt

First Published: October 2020

Last Revised: NA

Component Description

Chromium is considered both an essential element in trace amounts for carbohydrate metabolism and toxic in larger amounts (Cefalu et al., 2004). Chromium can be introduced into the human body via consumption of plants or supplements, degradation of metal-on-metal implants, and industrial exposure. For example, inhalation of chromium (VI) can damage the nose and cause lung cancer, and in drinking water has led to increased stomach ulcers (ATSDR, 2012).

Eligible Sample

All examined participants aged 3 to 5 years and a one-third subsample of examined participants aged 6 years and older were eligible.

Description of Laboratory Methodology

The method described in this document is for assessing multi-element exposure by analyzing urine using inductively coupled-plasma mass spectrometry (ICP-MS) (Tanner et al., 2002). This method achieves rapid and accurate quantification of urinary chromium. This method is used to screen urine when people are suspected to be acutely exposed to this element or to evaluate chronic environmental or other non-occupational exposure (Quarles et al., 2014).

Liquid samples are introduced into the ICP through a nebulizer and spray chamber carried by a flowing argon stream. By coupling radio-frequency power into flowing argon, a plasma is created in which the predominant species are positive argon ions and electrons and has a temperature of 6000-8000 K. The sample passes through a region of the plasma and the thermal energy atomizes the sample and then ionizes the atoms. The ions, along with the argon, enter the mass spectrometer through an interface that separates the ICP (at atmospheric pressure, ~760 torr) from the mass spectrometer (operating at a pressure of 10^-7 torr). In the NexION® ICP-MS, ions then pass through a focusing region, the Universal Cell Technology (UCT), the quadrupole mass filter, and finally are counted in rapid sequence at the detector allowing individual isotopes of an element to be determined.

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

There were no changes to the lab site or lab equipment for this component in the NHANES 2017-2018 cycle. There were changes to the lab method.

Laboratory Method Files

Arsenic, Chromium, and Nickel Urine Lab Procedure Manual (October 2020)

Laboratory Quality Assurance and Monitoring

Urine samples 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 (–30°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 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 on “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

Refer to the 2017-2018 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

The analytes included in this dataset were measured in all examined participants aged 3-5 years, and in a one-third subsample of participants 6 years and older. Special sample weights are required to analyze these data properly. Variable (WTSA2YR) encoding of the specific sample weights for this subsample is included in this data file and should be used when analyzing these data. These special sample weights were created to account for the subsample selection probability, as well as the additional nonresponse to these lab tests. Therefore, if participants were eligible for the subsample, but did not provide a urine specimen, they would have the sample weight value assigned as “0” in their records.

Demographic and Other Related Variables

The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2017-2018 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.

This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).

The variable URXUCR (urine creatinine) will not be reported in this file. URXUCR can be found in the data file titled Albumin & Creatinine – Urine.

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., URDUCMLC) indicates whether the result was below the limit of detection: “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 prefixed URX (ex., URXUCM) provides the analytic result for that analyte.  For analytes with analytic results below the lower limit of detection (ex., URDUCMLC=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 lower limit of detection (LLOD, in µg/L) for urinary chromium is:

Variable Name	Analyte Description	LLOD
URXUCM	Urinary Chromium	0.19

 

References

• Agency for Toxic Substances and Disease Registry (ATSDR), 2012. Toxicological profile for chromium. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
  
• Caudill S.P., Schleicher R.L., Pirkle J.L., Multi-rule quality control for the age-related eye disease study. Statist. Med. (2008) 27(30):4094-4106.
  
• Cefalu, W.T. and F.B. Hu, Role of chromium in human health and in diabetes. Diab. Care, 2004. 27: p. 2741-2751.
• Quarles Jr, C. D., Jones, Deanna R., Jarrett, Jeffery M., Shakirova, Gulchekhra., Pan, Yi.,Caldwell, Kathleen L., Jones, Robert L. (2014). "Analytical Method for Total Chromium and Nickel in Urine using an Inductively Coupled Plasma-Universal Cell Technology-Mass Spectrometer (ICP-UCT-MS) in Kinetic Energy Discrimination (KED) Mode." Journal of Analytical Atomic Spectrometry 29(2): 297-303.
• Tanner, S.D., V.I. Baranov, and D.R. Bandura, Reaction cells and collision cells for ICP-MS: a tutorial review. Spectrochimica Acta Part B-Atomic Spectroscopy, 2002. 57(9): p. 1361-1452.
  
• 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