The phlebotomy component of NHANES involved the collection of blood specimens. Prior to blood collection, the MEC phlebotomist administered a questionnaire to screen for conditions that would exclude participants from the blood draw. At this time, fasting status was determined. Blood specimens for basic hematology, nutritional biochemistry, and special studies were obtained.
Blood specimens were collected on participants aged one year and older in the Mobile Examination Center (MEC).
Participants aged 1 year and older were tested.
Description of Laboratory Methodology
The MEC phlebotomist drew blood from the participant’s arm. Participants with hemophilia or who received cancer chemotherapy in the past four weeks or will receive it in the future four weeks were excluded from the venipuncture.
Detailed phlebotomy collection and processing instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM). See Analytic Notes section for a general description of the fasting questions and calculation of fasting time in hours and minutes since the survey participant last ate or drank anything and the time of venipuncture draw.
Data Processing and Editing
Phlebotomy data were recorded directly into a computerized database; all forms used in the MEC were automated.
Laboratory Quality Assurance and Monitoring
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 theNHANES Laboratory/Medical Technologists Procedures Manual (LPM).
The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The Demographic file contains: Status Variables providing core information on the survey participant including examination status, Recoded Demographic Variables including age, gender, race etc., and Interview and Examination Sample Weight Variables and Survey Design Variables. The Questionnaire Data Files contain socio-economic data, health indicators, and other related information collected during household interviews. The Phlebotomy Examination file includes auxiliary information on duration of fasting, the time of day of the venipuncture, and the conditions precluding venipuncture. The Demographic, Questionnaire and Phlebotomy Examination files may be linked to the laboratory data file using the unique survey participant identifier SEQN.
Use PHAFSTHR and PHAFSTMN to determine the duration of fasting in hours and minutes, respectively. When calculating a fasting time in hours and minutes, pay careful attention to the other times in hours and minutes. For example, the survey participants were asked: "When was the last time you ate or drank anything other than plain water? Do not include diet soda or black coffee or tea with artificial sweeteners like Sweet'N Low, NutraSweet, Equal, or Splenda." Survey participants were then asked questions PHQ020 to PHQ060: "Have you had any of the following since the last time you ate or drank anything other than plain water? Coffee or tea with cream or sugar (Include milk or non-dairy creamers); Alcohol, such as beer, wine, or liquor; Gum, breath mints, lozenges, cough drops, or cold remedies; Antacids, laxatives, or anti-diarrheal; Dietary supplements such as vitamins and minerals."
If you are using fasting status in any of your analyses, please consider the answers to PHACOFHR/PHACOFMN, PHAALCHR/PHAALCMN, PHAGUMHR/PHAGUMMN/ PHAANTHR/PHAANTMN, and PHASUPHR/PHASUPMN with the times in hours and minutes in addition to the PHAFSTHR and PHSFSTMN times.
Use PHDSESN to determine the session in which the participant was examined.
MEC 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.