Reference values and participant means as targets in proficiency testing

Regulatory agencies will be placing greater reliance on the results of proficiency testing (PT) for determining licensing status of individual laboratories. This has caused a renewed interest in the process used by proficiency test providers for determining the correct result for each proficiency test challenge. Three general techniques have been proposed and would be allowed under the regulations: (1) participant-derived targets (means from a specific group of participants); (2) targets from a set of "reference" laboratories, from either a subset of participants or a selected group of experts using a rigorous experimental protocol; or (3) definitive values from a single source. The College of American Pathologists (CAP) has used all three techniques at different stages and for different purposes in the history of the CAP Surveys programs. This article reviews the early experiences of the CAP, the evolution of the current protocol, and activities to monitor the accuracy of target values. Participant-derived "consensus" results have been shown to be highly accurate and reliable. The CAP uses definitive methods at the National Institute for Standards and Technology and certified reference materials to monitor the validity of targets used in proficiency testing.