Proficiency Testing/External Quality Assessment: Current Challenges and Future Directions

Abstract

BACKGROUND: Proficiency testing (PT), or external quality assessment (EQA), is intended to verify on a recurring basis that laboratory results conform to expectations for the quality required for patient care.CONTENT: Key factors for interpreting PT/EQA results are knowledge of the commutability of the samples used and the process used for target value assignment. A commutable PT/EQA sample demonstrates the same numeric relationship between different measurement procedures as that expected for patients' samples. Noncommutable PT/EQA samples frequently have a matrix-related bias of unknown magnitude that limits interpretation of results. PT/EQA results for commutable samples can be used to assess accuracy against a reference measurement procedure or a designated comparison method. In addition, the agreement of the results between different measurement procedures for commutable samples reflects that which would be seen for patients' samples. PT/EQA results for noncommutable samples must be compared to a peer group mean/ median of results from participants who use measurement procedures that are expected to have the same or very similar matrix-related bias. Peer group evaluation is used to asses whether a laboratory is using a measurement procedure in conformance to the manufacturer's specifications and/or in conformance to other laboratories using the same technology. A noncommutable PT/EQA sample does not give meaningful information about the relationship of results for patients' samples between different measurement procedures.

Strategies to define performance specifications in laboratory medicine: 3 years on from the Milan Strategic Conference

“…In agreement with Infusino et al [25], the addition of PS derived from Milan models to the EQAS categorization previously published by Miller et al [26] as criteria to evaluate the performance of laboratories participating to EQAS should be promoted. Miller's categories 1 and 2, which fulfil the metrological requirements (commutable samples, valueassigned with reference measurement procedure), should be each split in two sub-categories: 1/2A, in which Milan models 1 and 2 for PS are applied, and 1/2B, in which other low-order models to establish PS are employed [25].…”

The quest for equivalence of test results: the pilgrimage of the Dutch Calibration 2.000 program for metrological traceability

“…With the above described approach and toolbox for standardization/harmonization of measurands, the Dutch EQA scheme organization SKML established a Category 1 EQA system [8,16], according to the criteria described in the 'Roadmap to Harmonization' paper [17,18]. According to the definition of a Category 1 EQA scheme [18] the SKML scheme uses commutable native sera with value assignment by reference methods and allows for verification of trueness and precision of IVD tests based on predefined tolerance limits of measurement errors to evaluate whether medical tests are fit-for-purpose [19].…”

“…According to the definition of a Category 1 EQA scheme [18] the SKML scheme uses commutable native sera with value assignment by reference methods and allows for verification of trueness and precision of IVD tests based on predefined tolerance limits of measurement errors to evaluate whether medical tests are fit-for-purpose [19]. It incorporates the following: 1.…”

“…Many papers address the issue and several initiatives were taken to improve the differences seen. In particular the AACC harmonization initiative [17,18], initiatives of IFCC and EFLM [24][25][26][27][28] and the installation of the JCTLM contributed significantly, as did the Calibration 2.000 project.…”

“…The need for sophisticated EQA was clearly indicated [18]. In Calibration 2.000 a Category 1 EQA scheme was developed using commutable samples that were value assigned with reference methods and covering the concentration range of interest, and using biological variation based trueness and imprecision tolerance limits including Six Sigma metric [8,16].…”