The objectives of this component are: 1) to provide data for monitoring secular trends in measures of nutritional status in the U.S. population; 2) to evaluate the effect of people's habits and behaviors such as dietary supplements on people's nutritional status; and 3) to evaluate the effect of changes in nutrition and public health policies including welfare reform legislation, food fortification policy, and child nutrition programs on the nutritional status of the U.S. population.
These data will be used to estimate deficiencies and toxicities of specific nutrients in the population and subgroups, to provide population reference data, and to estimate the contribution of diet, supplements, and other factors to serum levels of nutrients. Data will be used for research to further define nutrient requirements as well as optimal levels for disease prevention and health promotion.
Examined participants aged 1 year and older were eligible.
Serum is prepared for analysis by first combining the specimen 1:1 with a 5% solution of metaphosphoric acid to precipitate proteins out of the sample. After vortex mixing and centrifuging, the sample supernatant is combined with an approximately equivalent amount of dichloromethane to extract lipids from the sample, and vortex mixed and centrifuged a second time. The top (aqueous) layer from the sample is then filtered through a syringe and ready for high-performance liquid chromatographic (HPLC) HPLC analysis.
Vitamin B6, in the form of PLP, and the metabolite 4-PA are measured by reversed-phase HPLC using fluorometric detection at 325 nm excitation and 425 nm emissions. Post-column introduction of a sodium chlorite derivatization reagent is incorporated into the HPLC system to improve the PLP signal. Quantitation is based on analyte peak area interpolated against a five-point calibration curve obtained from aqueous standards.
Vitamin B6 (October 2015)
Serum specimens are processed, stored, and shipped to the 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 Amendments 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 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 National Center for Environmental Health’s quality control and quality assurance performance criteria for accuracy and precision, similar to the Westgard rules (Caudill, et al., 2008).
The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation. There are no derived variables, fill values, or recoding of data.
Read the Analytic Note in the Documentation from 2007-2008 for VITB6_E. Refer to the 2009-2010 Laboratory Data Overview for general information on NHANES laboratory data.
The analysis of NHANES 2009-2010 laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2009-2010 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).
Detection Limits
The detection limits were constant for this analyte in the data set.
Exam sample weights should be used for analyses. 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.
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 0.5 to 12200 | Range of Values | 8432 | 8432 | |
| . | Missing | 1403 | 9835 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 3.4 to 1320 | Range of Values | 8431 | 8431 | |
| . | Missing | 1404 | 9835 |