In 2010, a panel of federal scientists representing CDC/Division of Oral Health and National Institute of Dental (DOH) and Craniofacial Research (NIDCR) participated in the development of a new HHS recommendation for optimal fluoride level in drinking water (community water fluoridation), as well as development of guidelines for maximum fluoride levels in naturally fluoridated water. One of the recommendations of the federal panel was to strengthen the surveillance of dental caries and dental fluorosis with emphasis on determining fluoride exposures.
Examined participants aged birth to 19 years who had a water sample collected from their household were eligible.
Fluoride in Water:
Fluoride concentrations in water samples and appropriate aqueous standards are measured electrometrically using the ion-specific electrode. The limit of detection (LOD) of the electrode is ~1 µmole/L (0.019 mg/L), a concentration far below the concentration typically found in water. The linear portion of the standard curve extends from 0.1 mg/L to 19,000 mg/L at the electrode.
Refer to the Laboratory Method Files section for a detailed description of the laboratory methods used.
There were no changes to the lab method, lab equipment, or lab site for this component in the NHANES 2015-2016 cycle.
Fluoride - Water (September 2017)
Water samples are processed, stored, and shipped to the College of Dental Medicine, Georgia Regents University, Augusta, 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 Georgia Regents University for testing.
The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act 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
quality-control 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 quality control protocol for all CDC and contract
laboratories, which outlined the Westgard rules (Westgard et al., 1981) 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 College of Dental Medicine at Georgia Regents University’s quality control and quality assurance performance criteria for accuracy and precision, similar to the Westgard rules.
The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.
Refer to the 2015 - 2016 Laboratory Data Overview 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 2015-2016 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.
The laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).
Water fluoride was measured in duplicate, using the same sample. Since the variability between test results A and B is not statistically significant, the average of the two results are being released.
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., LBAWFLLC) 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. For analytes with analytic results below the lower limit of detection (ex., LBAWFLLC=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 other variable prefixed LBX (ex., LBXWFL) provides the analytic result for that analyte.The lower limit of detection (LLOD, in mg/L) for fluoride:
| Variable Name | SAS Label | LLOD |
|---|---|---|
| Fluoride, water, (Averaged) | LBDWFL | 0.10 |
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.