The NHANES program suspended field operations in March 2020 due to the coronavirus disease 2019 (COVID-19) pandemic. As a result, data collection for the NHANES 2019-2020 cycle was not completed and the collected data are not nationally representative. Therefore, data collected from 2019 to March 2020 were combined with data from the NHANES 2017-2018 cycle to form a nationally representative sample of NHANES 2017-March 2020 pre-pandemic data. These data are available to the public. Please refer to the Analytic Notes section for more details on the use of the data.
The fasting questionnaire is administered to determine the fasting status of the survey participant. Questions include but are not limited to: length of “food” fast, whether the participant had gum or mints, coffee or tea, or alcohol or dietary supplements prior to their laboratory examination.
All examined participants 1 year and older in the NHANES 2017-March 2020 pre-pandemic sample were eligible.
Description of Laboratory Methodology
The MEC phlebotomist administered the questionnaire to determine the fasting status of the survey participant.
Laboratory Quality Assurance and Monitoring
Detailed instructions on specimen collection and processing are discussed in the NHANES 2017-2018 and 2019-2020 NHANES Laboratory Procedures Manuals (LPM). 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 LPM.
Data Processing and Editing
Fasting questionnaire data were recorded directly into a computerized database; all forms used in the MEC were automated.
pandemic required suspension of NHANES 2019-2020 field operations in March 2020
after data were collected in 18 of the 30 survey locations in the 2019-2020
sample. Data collection was cancelled for the remaining 12 locations. Because
the collected data from 18 locations were not nationally representative, these
data were combined with data from the previous cycle (2017-2018) to create a
2017-March 2020 pre-pandemic data file. A special weighting process was applied
to the 2017-March 2020 pre-pandemic data file. The resulting sample weights in
the demographic data file should be used to calculate estimates from the
combined cycles. These sample weights are not appropriate for independent
analyses of the 2019-2020 data and will not yield nationally representative
results for either the 2017-2018 data alone or the 2019-March 2020 data alone.
Please refer to the NHANES website for additional information for the NHANES
2017-March 2020 pre-pandemic data, and for the previous 2017-2018 public use
data file with specific weights for that 2-year cycle.
Refer to the 2017-2018 and 2019-2020 Laboratory Data Overview documents for general information on NHANES laboratory data.
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-March 2020 Pre-Pandemic Demographics File contains demographic data, health
indicators, and other related information collected during household interviews
as well as the sample weight variables. The recommended procedure for variance
estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU,
respectively) in the demographic data file.
Questionnaire File includes auxiliary information such as fasting status, length
of fast, and the time of venipuncture.
This laboratory data file can be linked to the other NHANES
data files using the unique survey participant identifier (i.e., 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.
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.