• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Laboratory Method Files
• Laboratory Quality Assurance and Monitoring
• Data Processing and Editing
• Analytic Notes
• References
• Codebook
  • SEQN - Respondent sequence number
  • LBXWFL - Fluoride, water (mg/L)
  • LBDWFLLC - Fluoride, water comment code

National Health and Nutrition Examination Survey

2019-March 2020 Data Documentation, Codebook, and Frequencies

Fluoride - Water (FLDW_K_R)

RDC Only Data File: FLDW_K_R.xpt

First Published: December 2021

Last Revised: NA

Due to disclosure issues, this dataset is not available publicly. Access may be obtained through the NCHS Research Data Center (https://www.cdc.gov/rdc).

Component Description

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.  Data collected in 2019-March 2020 can be accessed as convenience samples through the NCHS Research Data Center (RDC). Any analyses based solely on the 2019-March 2020 data would not be generalizable to the U.S. civilian non-institutionalized population. Please refer to the Analytic Notes section for more details on the use of the data

The mineral fluoride is naturally occurring element in the earth that is released from rocks into the soil, water, and air. Fluoride levels in water are typically not enough to prevent tooth decay. Fluoride has been proven to protect teeth from decay (CDC, 2020).

Tooth decay is caused from bacteria in the mouth that produces acid when eating certain foods and drinks. This acid eats away at minerals on the tooth’s surface making the tooth weaker, which increases the chances of developing cavities. Fluoride helps to strengthen and even rebuild the enamel on the tooth’s surface. Water fluoridation helps prevent tooth decay by providing frequent and consistent contact with low levels of fluoride (CDC, 2020).

Community water fluoridation is the process of adjusting the amount of fluoride in drinking water to a level recommended for preventing tooth decay at safe consumption levels (CDC, 2020).

Toothpaste, mouth rinses, and dietary supplements containing fluoride are available and help with the prevention of tooth decay, community water fluoridation has been identified as the most cost-effective method of delivering fluoride to all, reducing tooth decay by 25% in children and adults (Griffin, et al. 2007).

Eligible Sample

All examined participants aged birth to 19 years who had a water sample collected from their household in the NHANES 2019-March 2020 convenience sample were eligible.

Description of Laboratory Methodology

Fluoride concentrations in water samples and appropriate aqueous standards are measured potentiometrically using the ion-specific electrode (ISE). The ISE is calibrated using fluoride solutions with known concentrations, such as calibrators.  Both calibrators and water samples are diluted with a total ionic strength adjustment buffer (TISAB) and measured under the same conditions. The TISAB contains an acetic acid/acetate buffer that adjusts the pH of the solution to approximately pH 5. At this pH the formation of HF is negligible and the concentration of OH-, the only other anion that the electrode responds to, is insignificant. It also contains NaCl to establish a high and constant ionic strength and a complexing agent that inhibits cations that could interfere by forming complexes with fluoride.

Refer to the Laboratory Method Files section for a detailed description of the laboratory methods used.

This is a new component in the 2019-2020 survey cycle.

Laboratory Method Files

Fluoride - Water (December 2021)

Laboratory Quality Assurance and Monitoring

Water samples are processed, stored, and shipped to the Division of Laboratory Sciences, 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 refrigerated (2-8°C) conditions until they are shipped to the 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 competency assessment evaluation during visits to evaluate both the quality of the laboratory work and the QC procedures. Each laboratory staff member is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff member. 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% of all specimens.

NCHS developed and distributed a QC protocol for all CDC and contract laboratories, which outlined the Westgard rules (Westgard et al., 1981) when testing 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 Division of Laboratory Sciences QA/QC performance criteria for accuracy and precision, similar to the Westgard rules (Caudill, et al. 2008). 

Data Processing and Editing

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

Analytic Notes

The COVID-19 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. Calculation of survey weights for this partial cycle is not possible due to incomplete data collection. Therefore, data from survey components that were only collected in 2019-March 2020 are made available as convenience samples through NCHS's Research Data Center (RDC) because unbiased estimates for the NHANES target population cannot be produced with these samples.

For survey components conducted in both 2017-2018 and 2019-2020 cycles, data collected from 2019 to March 2020 were combined with data from 2017 to 2018 to form a nationally representative sample of NHANES 2017-March 2020 pre-pandemic data. Please see the NHANES 2017-March 2020 pre-pandemic data page for detailed information on this combined sample.

Refer to the 2019 - 2020 Laboratory Data Overview for general information on NHANES laboratory data.

There are over 800 laboratory tests performed on NHANES participants. However, not all participants provided biospecimens or enough volume for all the tests to be performed. The specimen availability can also vary by age or other population characteristics. For example, in 2019-2020, approximately 71% of children aged 1-17 years who were examined in the MEC provided a blood specimen through phlebotomy, while 94% of examined adults age 18 and older provided a blood specimen. Analysts should be aware of this and evaluate the extent of missing data in the dataset related to the outcome of interest as well as any predictor variables used in the analyses as needed.

Demographic and Other Related Variables

The analysis of NHANES laboratory data may require additional demographic variables. The NHANES 2019- March 2020 Demographics File contains demographic data, health indicators, and other related information collected during household interviews.

The laboratory data file can be linked to the Demographics file and other NHANES data files in the 2019-March 2020 convenience sample  using the unique survey participant identifier (i.e., SEQN).

Detection Limits

The detection limits were constant for the analyte in the data set. Two variables are provided for each of these analytes. The variable name ending “LC” (ex., LBDWFLLC) indicates whether the result was below the limit of detection: the value “0” means that the result was at or above the limit of detection, “1” indicates that the result was below the limit of detection. The other variable prefixed LBX (ex., LBXWFL) provides the analytic result for that analyte.  For analytes with analytic results below the lower limit of detection (ex., LBDWFLLC=1), an imputed fill value was placed in the analyte results field. This value is the lower limit of detection divided by the square root of 2 (LLOD/sqrt[2]).  The lower limit of detection (LLOD, in mg/L) for fluoride:

Analyte	Analyte Description	LLOD
Fluoride, water	LBXWFL	0.024

References

• Caudill, S.P., Schleicher, R.L., Pirkle, J.L. Multi-rule quality control for the age-related eye disease study. Statist. Med. (2008) 27(20):4094-40106.
• CDC. Community Water Fluoridation: Water Fluoridation Basics. 2020. Accessed on September 23, 2020 from https://www.cdc.gov/fluoridation/basics/index.htm
• Griffin SO, Regnier E, Griffin PM, Huntley VN. Effectiveness of fluoride in preventing caries in adults. J Dent Res. 2007;86(5):410–414.
• Westgard J.O., Barry P.L., Hunt M.R., Groth T. A multi-rule Shewhart chart for quality control in clinical chemistry. Clin Chem (1981) 27:493-501.

Codebook and Frequencies