Water Fluoride Laboratory Proficiency Testing Program

CDC’s national Water Fluoride Laboratory Proficiency Testing (PT) Program verifies analytical accuracy of state laboratories’ fluoride testing by comparing their results with those of reference laboratories.

Measuring the fluoride content of drinking water requires precision and attention to detail, because the low fluoride concentration in most water is near the lower limit of measurement methods used by many laboratories.

A laboratory verification program is important to validate analytical methodology and to identify errors so laboratories can correct them. Participating state laboratories provide a reference on quality control for water treatment facilities in their states or service jurisdictions. CDC’s PT program verifies that the methodology of the state laboratory achieves a quality standard.

State Split-Sample Programs

While managers of community water systems test fluoride content daily, they also periodically collect a sample, typically every month, split the sample into two parts, test one part on site, and send the other to a state laboratory for verification testing. This comparison allows the water system to know if its laboratory technique is correct and if the results it is reporting are accurate.

The aim of the PT Program is to verify the quality of these state laboratories and to monitor their continuing performance in fluoride testing.

Laboratory Proficiency Testing Basics

Proficiency testing is the use of inter-laboratory comparisons to determine the performance of individual laboratories for specific tests and to monitor laboratory’s continuing performance. CDC’s Laboratory PT program is consistent with the requirement of ISO 43-1:1997E published by the International Organization for Standardization.* The U.S. Environmental Protection Agency (EPA) also has a laboratory quality assurance for potable water testing criteria for regulatory compliance reporting based on associated ISO criteria. CDC has operated the PT Program for more than 20 years.

The PT Program assesses a laboratory’s performance by its ability to determine an accurate fluoride measurement against a known standard sample. This is an important quality assessment scheme that assures public health staff and citizens that drinking water fluoride levels are safe and properly monitored on a daily basis. If a laboratory is found to lack proficiency, this means that there is opportunity for improvement.

CDC Reference Rounds

Each calendar quarter, CDC prepares nine samples of reference solutions (36 samples annually) with known concentrations of fluoride and provides these to state and reference laboratories. Six laboratories are designated as reference laboratories, and analyze each reference solution twice a day for four sequential days for a total of eight times. The 48 individual results for each sample (6 laboratories measure each sample eight times over four sequential days) are statistically compared with the known solution concentration to establish a “reference round” solution quality standard.

Each month, the state laboratories analyze three of the reference samples and report the fluoride concentration measurements to CDC. At the end of a reference round, CDC provides the state laboratories with a report of the submitted results (mg/L), target fluoride concentrations (mg/L), and whether the results were in the acceptable range for accuracy (yes/no). Comparison data from other state laboratories also are provided.

This overview of the PT Program (PDF–276K) explains the basic sequence of activities in the process.

The CDC Data Management System

CDC uses a Web-based submission and reporting system. Program data are handled by a CDC database known as the Proficiency Testing System (PTS). In addition to serving as a data submission and reporting tool, it notifies participating laboratories of the initiation of a round when samples are mailed, notifies them when results must be submitted, and generates reports to users. Participating laboratories must qualify as a state laboratory for their jurisdiction and if accepted into the program, users must register for access privileges. See the PowerPoint presentation on the use of the PTS. (PPT–483K)  (PDF–456K)

Program Reports

The program report is a unique report on the results of that particular state laboratory, and data from other laboratories included for comparison purposes are anonymous. The PTS automatically generates the discrete reports to the state laboratories and state dental directors. Parties that may have an interest in the data must request the data from each state individually. States normally release information through the state dental director, in accordance with the policies of their state information management protocols.

CDC cannot issue the results through channels other than the state dental directors,* since the reports are automatically generated and sent to the laboratories and state dental director.

One or more documents on this Web page is available in Microsoft PowerPoint (PPT). You will need PowerPoint Viewer to view and print these documents.

One or more documents on this Web page is available in Portable Document Format (PDF). You will need Acrobat Reader to view and print these documents.

* Links to non-Federal organizations are provided solely as a service to our users. Links do not constitute an endorsement of any organization by CDC or the Federal Government, and none should be inferred. The CDC is not responsible for the content of the individual organization Web pages found at this link.

Page last reviewed: December 26, 2007
Page last updated: January 3, 2008
Content source: Division of Oral Health, National Center for Chronic Disease Prevention and Health Promotion