National Health and Nutrition Examination Survey

Trace metals have been associated with adverse health effects in occupational studies or laboratory studies, but have not been monitored in general population groups.

This method is used to achieve rapid and accurate quantifications of three elements of toxicological and nutritional interest. The method is sensitive and rapid enough to screen serum specimens from subjects suspected to be exposed to a number of important toxic elements, or to evaluate environmental or other nonoccupational exposure to these same elements.

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

Serum 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).

Inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) is a multi-element analytical technique capable of trace level elemental analysis. This ICP-DRC-MS method is used to measure the entire panel of the 3 elements, or any subgroup of these. 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, plasma is created, in which the predominant species are positive argon ions and electrons, and has a temperature of 6,000-8,000 °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 10-5 torr). The ions pass through a focusing region, the dynamic reaction cell (DRC), the quadrupole mass filter, and finally are counted in rapid sequence at the detector allowing individual isotopes of an element to be determined. In this method, the instrument is operated in ‘DRC’ mode where the cell is pressurized with 99.99+% ammonia gases, which collides or reacts with the incoming ions to eliminate interfering ions and leave the ion of interest to be detected. After leaving the DRC cell, the ions are focused with ion optics into a quadrupole mass analyzer with a nominal mass resolution of 0.7amu. The quadrupole is sequentially scanned to specific mass to charge ratio of each analyte and intensity is detected with a pulse detector. Electrical signals resulting from the detection of ions are processed into digital information that is used to indicate first, the intensity of the ions and second, the concentration of the element. This method was originally based on the methods by Piraner and Walters and the DRC portions of the method are based on work published by Tanner et al. The isotopes measured by this method include zinc (m/z 64), copper (m/z 65), and selenium (m/z 78) and the internal standard gallium (m/z 71). Serum samples are diluted 1+1+28 with water and diluent containing gallium (Ga) for multi-internal standardization.

Serum copper, selenium, and zinc were first tested in NHANES in 2011-2012.

Refer to NHANES 2011-2012 Lab Methods for Zinc, Copper and Selenium for detailed description of the laboratory method used.

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

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES Laboratory Procedures Manual (LPM)

Refer to the 2011-2012 Laboratory Data Overview for general information on NHANES laboratory data.

The analysis of NHANES 2011-2012 laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2011-2012 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample weight variables. The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture. The demographics and fasting questionnaire files may be linked to the laboratory data file using the unique survey participant identifier (i.e., SEQN).

Subsample Weights

Serum copper, selenium, and zinc were measured in a one third subsample of participants aged 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

All the data was above the lower limit of detection (LLOD) for all three tests. The LLODs are as follows: serum copper 2.5 µg/dL; serum selenium 4.5 µg/L; serum zinc 2.9 µg/dL.

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.