The objectives of this component are to:
1) Provide data for monitoring secular trends in measures of nutritional status in the U.S. population;
2) Evaluate the effect of people's habits and behaviors such as physical activity and the use of alcohol, tobacco, and dietary supplements on people's nutritional status; and
3) 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 Whole Blood 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.
Participants aged 1 year and over were tested.
Description of Laboratory Methodology
Blood specimens were measured at the NHANES Mobile Examination Centers (MECs). Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).
The methods used to derive CBC parameters are based on the Beckman Coulter method of counting and sizing, in combination with an automatic diluting and mixing device for sample processing, and a single beam photometer for hemoglobinometry. The WBC differential uses VCS technology. See Chapter 7 of the NHANES Laboratory/Medical Technologists Procedures Manual (LPM) for details.
The Beckman Coulter MAXM instrument in the MECs produces a complete blood count on blood specimens and provides a distribution of blood cells for all participants.
There were no changes to the lab methods, or lab site from the previous 2 years.
A detailed description of the laboratory method used can be found on the NHANES website.
Data Processing and Editing
Read the Laboratory Data Overview file for detailed data processing and editing protocols. The analytical methods are described in the Description of the Laboratory Methodology section.
Five derived variables were created in this data file. The formula for their derivation is as follows:
LBDLYMNO = LBXWBCSI * LBXLYPCT/100 (round to 1 decimal)
LBDMONO = LBXWBCSI * LBXMOPCT/100 (round to 1 decimal)
LBDNENO = LBXWBCSI * LBXNEPCT /100 (round to 1 decimal)
LBDEONO = LBXWBCSI * LBXEOPCT/100 (round to 1 decimal)
LBDBANO = LBXWBCSI * LBXBAPCT/100 (round to 1 decimal)
Laboratory Quality Assurance and Monitoring
The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed quality control and quality assurance instructions are discussed in the NHANES LPM. Read the Laboratory Data Overview file for detailed QA/QC protocols.
A detailed description of the quality assurance and quality control procedures can be found on the NHANES website.
Refer to the 2011-2012 Laboratory Data Overview for general information on NHANES laboratory data.
Several CBC tests have shown trends since NHANES 2005-2006. These trends were seen in the total sample and across gender and age groups indicating possible method issues. The weighted mean platelet count was approximately 290000 in NHANES 2005-2006 and decreased to 245000 in NHANES 2011-2012. This trend in decreasing platelets has been acknowledged by the manufacturer (Beckman Coulter, Inc.) and is being actively being investigated by the manufacturer. The weighted mean hematocrit decreased from 42.1% in NHANES 2005-2006 to 40.6% in NHANES 2011-2012. This was most likely due to a change in the anticoagulant EDTA. K3 EDTA shrinks the red blood cells more than K2 EDTA resulting in lower hematocrit. The weighted mean red blood count decreased from 4.7x106 cells/uL in NHANES 2005-2006 to 4.57x106 cells/uL in NHANES 2011-2012. This may also be due to the change in EDTA. The weighted mean MCHC has increased from 33.9 g/dL in NHANES 2005-2006 to 34.3 g/dL in NHANES 2011-2012. This was the result of the decrease in hematocrit since MCHC=hemoglobin/hematocrit. The weighted mean white blood count has decreased from 7.40 103 cells/uL in NHANES 2005-2006 to 7.03x103 cells/uL in NHANES 2011-2012. This was not seen by the manufacturer and will be investigated.
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).
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.