The correlation of laboratory performance in proficiency testing with other QA characteristics

Although it seems self-evident that proficiency testing (PT) and accreditation can be expected to improve quality, their relative benefits remain uncertain as does their efficacy. The study reported here examines the following issues: (a) Why do laboratories take part in PT schemes? (b) How does participation in PT fit in with a laboratory's overall quality assurance (QA) system? (c) Is there a link between a laboratory's performance in specific PT and it's QA system? (d) How does PT performance change with time and how do laboratories respond to poor performance? The overall conclusion is that there is no evidence from the present study that laboratories with third-party assessment (accreditation and certification) perform any better in PT than laboratories without. The validity of this conclusion and its significance for the future design and operation of such schemes requires further investigation. In particular, study is required of the degree to which good performance in open PT correlates with blind PT performance, where laboratories are not aware that the samples being analysed are part of a quality assessment exercise.     

Information system and qualifying criteria for proficiency testing schemes

Since October 1998 the European Commission has financed a concerted action on Information System and Qualifying Criteria for Proficiency Testing Schemes within the 4th framework program. As a major result of this project EPTIS, the European Information System on Proficiency Testing Schemes which is available on the Internet since March 2000, is presented in this paper. Today EPTIS contains comprehensive information on approximately 640 proficiency testing schemes from 16 European countries providing information on the state of the art in proficiency testing in Europe. Finally some possible approaches for interlinkages and recognition of proficiency testing schemes are discussed.     

Statistical treatment of proficiency testing data

 There are three stages to evaluating a laboratory's results in an interlaboratory proficiency test: establishing the correct result for the test item, determining an evaluation statistic for the particular result, and establishing an acceptable range. There are a wide variety of procedures for accomplishing these three stages and a correspondingly wide variety of statistical techniques in use. Currently in North America the largest number of laboratory proficiency test programs are in the clinical laboratory field, followed by programs for environmental laboratories that test drinking water and waste water. Proficiency testing in both of these fields is under the jurisdiction of the federal government and other regulatory and accreditation agencies. Many of the statistical procedures are specified in the regulations, to assure comparability of different programs and a fair evaluation of performance. In this article statistical procedures recommended in International Organization for Standardization Guide 43, Part 1, are discussed and compared with current practices in North America. Received: 22 April 1998 · Accepted: 12 May 1998     

The rational use of proficiency tests and intercomparisons

 Interlaboratory comparisons (in the following abbreviated as intercomparisons) regarding tests, analyses or measurements are among the most worthwhile measures a laboratory can take in order to confirm that its services to clients include the provision of correct results within a stated uncertainty. They give a picture of the whole performance of the laboratory, and they should be used much more than at present. Unfortunately such intercomparisons are, and are made, expensive and prestigious by the formalisms employed in many cases. The connection between intercomparisons and proficiency tests and their use for different purposes is briefly discussed. Some suggestions are made on how to improve the present state of the art, i.e. how to increase the use of intercomparisons, how to perform them efficiently and how to make optimal use of the results. Received: 6 December 1997 · Accepted: 30 January 1998     

Benefits arising from proficiency testing schemes: The comparison of analytical methods

 The primary objective of proficiency testing (PT) is in the provision of information and support to participating laboratories, to enable them to monitor and improve the quality of their measurements. However, other benefits can be obtained from PT. These include the comparison of data for a given measurement by different methods, the validation of new methods, and the provision of information for laboratories' customers and accreditation bodies. This paper considers the subject of method comparison, and highlights some of the approaches which can be followed, as well as the practical use to which this can be put, to benefit the analytical community more widely. This is illustrated by a case study concerning the measurement of haze in beer. In this study the United Kingdom Institute of Brewing (IoB) conducted a survey of participants in the Brewing Analytes Proficiency Scheme (BAPS). From the survey data taken together with data from the BAPS scheme, the IoB is now in a position to give guidance on the use of particular instruments and procedures, as well as consider changes to the scope of the BAPS scheme to provide greater benefits for participants concerned with measuring haze. Received: 3 March 1998 · Accepted: 9 June 1998     

Experiences from the assessment of proficiency testing providers

Following a pilot project in 2001–2002, UKAS accredited nine PT providers. During the course of the pilot and at subsequent surveillance visits, UKAS has gained experience in assessing organisations against the criteria detailed within ISO/IEC Guide 43-1:1997 and ILAC G13:2000. This article explores some of the key aspects that arose during the pilot and how UKAS has accommodated the addition of the accreditation of PT providers in to its range of services.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Quality issues in proficiency testing

 Proficiency testing is a means of assessing the ability of laboratories to competently perform specific tests and/or measurements. It supplements a laboratory's own internal quality control procedure by providing an additional external audit of their testing capability and provides laboratories with a sound basis for continuous improvement. It is also a means towards achieving comparability of measurement between laboratories. Participation is one of the few ways in which a laboratory can compare its performance with that of other laboratories. Good performance in proficiency testing schemes provides independent evidence and hence reassurance to the laboratory and its clients that its procedures, test methods and other laboratory operations are under control. For test results to have any credibility, they must be traceable to a standard of measurement, preferably in terms of SI units, and must be accompanied by a statement of uncertainty. Analytical chemists are coming to realise that this is just as true in their field as it is for physical measurements, and applies equally to proficiency testing results and laboratory test reports. Recent approaches toward ensuring the quality and comparability of proficiency testing schemes and the means of evaluating proficiency test results are described. These have led to the drafting of guidelines and subsequently to the development of international requirements for the competence of scheme providers. Received: 2 January 1999 · Accepted: 7 April 1999     

The practice of proficiency testing in China

This paper briefly summarises the current situation for proficiency testing (PT) in China, outlines the policy for PT of China’s national accreditation committee for laboratories (CNACL), and exemplifies activities of the CNACL’s metal working group. Received: 9 December 2000 Accepted: 14 December 2000     

Economy of proficiency testing: reference versus consensus values

Many proficiency tests are operated with a consensus value derived from the participants’ results. Apart from technical issues, one of the reasons often mentioned is that proficiency tests operated with consensus values would be cheaper than those using reference values obtained from a priori characterisation measurements. The economy of a proficiency test must of course be balanced by the need of the participants, and the quality of the comparison in general. The proficiency tests selected in this study had both a reference value and a consensus value, one of which was used for assessing the performance of the participating laboratories. In this work, both a technical and an economical assessment of how the comparisons were operated is made. From the evaluation, it follows that usually the use of consensus values does not necessarily reduce the costs of a proficiency test. However, frequently it may be observed that the quality of the assessment of the laboratories is better with a reference value. Received: 11 October 2000 Accepted: 3 January 2001     

Definition of assigned values for proficiency tests in water analysis

The definition of an assigned value is usually achieved by calculating mean values from the data (with different methods) or by designating reference laboratories. Neither method is completely satisfactory. In this paper a new method is presented for the definition of the assigned value for spiked samples with an unknown content of the analyte in the matrix. The method consists of two parts. The first is the estimation of the assigned values from the spiked amounts and the content in the matrix, based on the results of reference laboratories. The other is the designation of these reference laboratories by comparing their results with the assigned values. Because each of these parts requires the other, an iterative procedure is necessary. As an example, the results of a proficiency test for the analysis of copper in wastewater are used to compare the calculated values with those from other methods, e.g., the Huber estimation. Received: 25 September 2000 Accepted: 9 December 2000     

Reliability of food measurements: the application of proficiency testing to GMO analysis

This paper reviews the experience of the Food Analysis Performance Assessment Scheme (FAPAS^®) in operating a proficiency testing scheme for the analysis of genetically modified (GM) food. Initial rounds of proficiency testing have shown a tendency for laboratories to over-estimate GM levels, results obtained by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) detection methods to be significantly different and that data are skewed and not normally distributed until log-transformed. During the initial rounds, it was found that for analysis and quantification of GM material, it was not possible to assign a target value for standard deviation external to the round data, from which performance could be assessed. However, when working in a log scale, the internally derived, robust standard deviation (^σ) was found to be constant and could be used directly to predict a target value (σ) for performance assessment. Results from the first four rounds have provided valuable information and a general overview of laboratory ability. Choosing a target value for standard deviation which reflects current best practice has enabled laboratory performance to be assessed. Issues surrounding the assessment of performance are discussed which highlight some of the implications raised as a result of this initial assessment, regarding the enforcement of European labelling legislation.     

Proficiency testing in analytical chemistry, microbiology, and laboratory medicine – working group discussions on current status, problems, and future directions

Working group (WG) discussions on proficiency testing (PT) held at the joint Eurachem/ EQALM workshop, Borås, Sweden, 24–26 September 2000 are summarized. The discussions focused on aspects of PT and accreditation (WG 1), general aspects of PT in analytical chemistry (WG 2), microbiology (WG 3), and laboratory medicine (WG 4), incorporation of measurement uncertainty into PT schemes (WG 5), international harmonization of PT schemes (WG 6), and the role of PT in the international structure of chemical measurement (WG 7). Current status, problems and future directions are identified. Each WG contained a majority of participants experienced in the subject being covered by that WG, and a few participants with different expertise. This was done to promote cross-fertilization of ideas between sectors, a key objective of the workshop. The WG issues reflected the content of the keynote lectures and some issues were covered from different perspectives by more than one group.     

Advances for proficiency testing for genetic laboratory science

Nucleic acid based clinical genetic testing has undergone explosive growth in recent years due in large part to the human genome project. Characterization of the human genome has led to a molecular understanding of the pathogenesis of many human diseases, and ultimately to clinical molecular tests becoming routinely used to diagnose a wide diversity of diseases. This rapid growth in clinical molecular genetic testing coupled with the complexity of the analytical procedures underscores the necessity for proficiency testing (i.e. external quality assessment) to allow laboratories offering such services the ability to evaluate their analytical procedures via inter-laboratory comparisons. The American College of Medical Genetics (ACMG) in partnership with the College of American Pathologists (CAP) have been offering proficiency testing for clinical molecular genetics laboratories since 1995, and presently have more than 230 laboratories from 11 countries enrolled in this program. This paper describes the evolution of this program and several challenges encountered in the delivery of a proficiency testing program for laboratories offering clinical molecular genetic services. Received: 13 April 2002 Accepted: 18 July 2002     

An error model for evaluation and interpretation of proficiency testing

Data from proficiency testing can be used to increase our knowledge of the performance of populations of laboratories, individual laboratories and different measurement methods. To support the evaluation and interpretation of results from proficiency testing an error model containing different random and systematic components is presented. From a single round of a proficiency testing scheme the total variation in a population of laboratories can be estimated. With results from several rounds the random variation can be separated into a laboratory and time component and for individual laboratories it is then also possible to evaluate stability and bias in relation to the population mean. By comparing results from laboratories using different methods systematic differences between methods may be indicated. By using results from several rounds a systematic difference can be partitioned into two components: a common systematic difference, possibly depending on the level, and a sample-specific component. It is essential to distinguish between these two components as the former may be eliminated by a correction while the latter must be treated as a random component in the evaluation of uncertainty. Received: 20 November 2000 Accepted: 3 January 2001     

Uncertainty evaluation in proficiency testing: state-of-the-art, challenges, and perspectives

The evaluation of measurement uncertainty, and that of uncertainty statements of participating laboratories will be a challenge to be met in the coming years. The publication of ISO 17025 has led to the situation that testing laboratories should, to a certain extent, meet the same requirements regarding measurement uncertainty and traceability. As a consequence, proficiency test organizers should deal with the issues measurement uncertainty and traceability as well. Two common statistical models used in proficiency testing are revisited to explore the options to include the evaluation of the measurement uncertainty of the PTRV (proficiency test reference value). Furthermore, the use of this PTRV and its uncertainty estimate for assessing the uncertainty statements of the participants for the two models will be discussed. It is concluded that in analogy to Key Comparisons it is feasible to implement proficiency tests in such a way, that the new requirements can be met. Received: 29 September 2000 Accepted: 3 December 2000     

Microbiological proficiency testing: a personal perspective

The author considers the fundamental differences between analyses in microbiology and those in chemistry and physics, deducing special issues for microbiological proficiency testing. He concludes that the variability and uncertainty implicit in microbiological analysis requires a broader range of proficiency scheme providers providing a broader range of services than in chemistry and physics. Received: 10 November 2000 Accepted: 3 December 2000     

Requirements vs acceptability in proficiency testing schemes and other interlaboratory comparisons

Many laboratories take part in proficiency testing schemes, external quality assessment programmes and other interlaboratory comparisons. These have many similarities but also important differences in their modus operandi and evaluation of performance of participating laboratories. This paper attempts to highlight both the similarities and differences. It also puts particular emphasis on requirements called ”target values for uncertainty” and their meaning. Received: 24 January 2001 Accepted: 25 January 2001     

Evaluation of proficiency testing results taking into account their uncertainties

A new composite score for the evaluation of performance of proficiency testing participants is proposed. The score is based on a combination of the z-score, uncertainty of a participant’s measurement result and uncertainty of the proficiency testing scheme’s assigned value. The use of such a composite score will allow evaluation not only of the participant’s ability to determine an analyte in corresponding matrix, but also their understanding of the uncertainty in the obtained analytical result. The score may be helpful for the laboratory’s quality system and for laboratory accreditation according to ISO 17025.     

Proficiency testing as tool for ISO 17025 implementation in National Public Health Laboratory: a mean for improving efficiency

Public Health Laboratories (PHL) as part of Public Health Services are involved in law enforcement and ensuring food and water quality. The laboratories had to go through an organizational and monetary change imposed by the growing and changing needs of the state of Israel. The laboratories had to become more modern and to implement new and more sophisticated testing methods. Another requirement was to perform a steadily increasing number of tests and to be more flexible towards customers’ demands. Yet, the budget was not changed accordingly, as the Public Service to which the laboratories belong to do not respond to changing needs. Management realization was that the accreditation process could be used as a tool to achieve organizational and cultural change. Understanding and transformation were required throughout the organization, including management. Proficiency testing is performed for all testing methods in all areas even for non-accredited tests such as clinical tests. Proficiency testing was used as a tool for organizational culture change. It is a great index with game elements, that gives employees and managers the possibility for comparison, fixing problems and corrective action. The demands of ISO 17025 made it necessary to change peoples’ attitudes and views on both professional and communication levels. Laboratory quality consists now on the four main principles, described in the 5M&E model which is typical to small organizations and which ensures a constantly improving system: ”Policy statement”, ”Machine”, ”Material”, ”Measurement”, ”Method”, ”Manpower”, and ”Environment” targeted to achieve ”Quality upgrade”. Slowly we succeeded in providing better and more reliable services and have increased our income on what would hopefully become our way to financial independence. We hope this process would provide the Ministry of Health with a better chance to public health using the same financial sources. Received: 25 October 2000 Accepted: 12 December 2000     

Quality in clinical laboratory measurements

 Clinical chemistry deals with measurements and observations using samples from patients in order to supply clinicians with information to support their decisions in diagnosis and treatment. The discipline utilizes advanced chemical and biochemical methods and also sophisticated instrumentation which allows a high throughput. Clinical chemistry has a long tradition of quality assessment and improvement. The major tools have been proficiency testing or external quality assessment and internal quality control. Nowadays, total quality management has become widely recognized, and accreditation according to international, regional or national schemes has contributed to the design of quality systems and improvement of the reliability of results from clinical laboratories.