By Jane Gun-Munro, Director, EQA
External Quality Assessment (EQA) and Proficiency Testing (PT) providers are required to periodically review allowable limits of performance (ALPs) set for quantitative schemes to confirm appropriate evaluation of participant performance. Most performance limits are based on achievable performance of methods being used; a few, such as hemoglobin A1c (HbA1c) or cholesterol, are based on clinical needs.
A review of the current Quality Management Program—Laboratory Services (QMP–LS) limits was undertaken in 2011. The review included comparison of EQA limits with those established for other EQA providers (CLIA, Royal College of Pathologists of Australasia [RCPA]) as well as limits based on biological variation data. Participant result data for analytes from previous EQA surveys were used to evaluate achievable performance with the different limits using Per cent Allowed Difference (PAD) scores as well as Z scores. This information was presented to the chemistry and hematology committees for decisions regarding establishment of revised performance limits. For some analytes, the current performance limits were confirmed as being acceptable; for others it was agreed that the limits should be altered. These new limits will be published in updated versions of the chemistry and hematology program information documents and implemented in April 2012.
The comparison of PAD scores with Z scores also provided an opportunity to review their effectiveness in determining when laboratories need to investigate and take action. PAD scores were introduced as a tool for performance evaluation of quantitative EQA surveys in 2008. It therefore seemed timely to review their use in 2011. Since the QMP–LS limits were found to be similar to other EQA provider performance limits, it follows that investigation and corrective action should be required when the PAD score is 100% or greater, and yet our current action point (A1) is 150%.
For these reasons, QMP–LS has determined that starting in April 2012, the action limit for quantitative surveys will be revised to 100% and a new code (A0) will replace the warning code (W1). This will appear on the participant survey report and trigger the generation of the online discordant finding investigation form. Participants will be expected to submit a completed form. The discordant finding investigation form will then become a permanent record of each laboratory’s investigation and will be available for committee review when required.