Proficiency testing importance

As the use of RMs increases and international trade in these materials becomes established, it has become clear that they can be subject to high levels of import duty and delay when clearing customs. In 1998 ISO/REMCO established Task Group 6 to investigate the problems involved in shipping reference materials (and materials that are in the process of being made into reference materials, such as proficiency testing materials) across national boimdaries. 

Table 14 can be regarded as providing a reasonable overall picture, even if the results cannot applied to any particular case. However, if the underlying principle is accepted, it becomes clear that improvements in a single stage, for example the reduction of instrument variation, has a negligible beneficial effect (if this variation was not outside the normal range ). Even if the contribution of repeatability is re-duced to zero, the cumulative uncertainty is reduced by 10% only, i.e. from 2.2 to y(0.0)2 (0.8)2 (1.0)2 + (1.5)2 = 2.0. This statistical view of errors should help to avoid some unnecessary efforts to improve, e.g., calibration. Additionally, this broad view on all sources of error may help to detect the most important ones. Consequently, without participation in proficiency tests, any method validation will remain incomplete. 

This chapter deals with handling the data generated by analytical methods. The first section describes the key statistical parameters used to summarize and describe data sets. These parameters are important, as they are essential for many of the quality assurance activities described in this book. It is impossible to carry out effective method validation, evaluate measurement uncertainty, construct and interpret control charts or evaluate the data from proficiency testing schemes without some knowledge of basic statistics. This chapter also describes the use of control charts in monitoring the performance of measurements over a period of time. Finally, the concept of measurement uncertainty is introduced. The importance of evaluating uncertainty is explained and a systematic approach to evaluating uncertainty is described. 

All proficiency testing schemes should have a statistical protocol which states clearly how the data will be processed and how laboratory performance will be evaluated. This protocol should also describe how the assigned value for any parameter in a test sample is estimated. This is an important consideration, as the performance of individual laboratories is gauged by comparison with the assigned value. 

This chapter has considered two of the types of interlaboratory comparison exercise in which your laboratory may participate. It is important to remember that proficiency testing schemes and collaborative studies have different aims. The former is a test of the performance of the laboratory, whereas the latter is used to evaluate the performance of a particular analytical method. Laboratories should participate in proficiency testing schemes (where an appropriate scheme is available) as this provides an independent check of the laboratory s performance. This chapter has described the key features of proficiency testing schemes and explained how the results from participation in a scheme should be interpreted. 

The need for laboratories carrying out analytical determinations to demonstrate that they are doing so competently has become paramount. It may well be necessary for such laboratories not only to become accredited and to use fully validated methods but also to participate successfully in proficiency testing schemes. Thus, proficiency testing has assumed a far greater importance than previously. 

There are different reasons for interlaboratory tests. One is method validation, e.g. prior to the standardization of characterization of reference materials, which have to be certified. The third and most important for quahty assurance is proficiency testing of laboratories. There are different requirements for each type of interlaboratory test. 

There are some guidelines on the requirements for proficiency testing schemes. The most important is the new ISO/IEC 17043 Conformity assessment - General requirements for proficiency testing . It describes the development and operation of a PT scheme with all quality management requirements related to that. The first version of the International Harmonized Protocol for the Proficiency Testing of (Chemical) Analytical Laboratories was a result of a joint workshop of lUPAC, ISO and AOAC and was published in 1993. A 2nd, revised version was published in 2006. This protocol also sets out the requirements for the provider and for the PT scheme itself. 

Traditionally, the education that chemists and chemistry laboratory technicians receive in colleges and universities does not prepare them adequately for some important aspects of the real world of work in their chosen field. Today s industrial laboratory analyst is deeply involved with such job issues as quality control, quality assurance, ISO 9000, standard operating procedures, calibration, standard reference materials, statistical control, control charts, proficiency testing, validation, system suitability, chain of custody, good laboratory practices, protocol, and audits. Yet, most of these terms are foreign to the college graduate and the new employee. 

Radiation monitoring laboratories seeking to achieve optimum proficiency test results with an accreditation standard must use calibration methods that duplicate or at least closely approximate the irradiation protocols described in the accreditation standard. This requirement is particularly important for calibrations using photons with energies below 200 keV where irradiation conditions must recreate the scattered radiation that contributes significantly to the response of the monitoring device. 

Participation in proficiency tests is not a prerequisite or an absolute substitute for IQC measures or vice versa. However, participance in proficiency tests is meaningless without a well-developed IQC system. IQC underlies participance in PT schemes, while IQC and participance in PT schemes are both important substitutes of AQA (Figure 6). It is shown that laboratories with the strongest QC procedures score significantly better in PT schemes [8,50]. Participance in PT can to a certain extent improve the laboratory s performance however unsatisfactory performance in schemes (up to 30% of all participants) has been reported. This means that there... 

Some important assays commonly used in biochemical genetics laboratories do not provide quantitative data (e.g. MPS-EP, qualitative urinary organic acid analysis, AA-TLC). In addition, all successful investigations depend heavily upon selection of the correct analytes to measure and the appropriate interpretation of the quantitative or qualitative results in their clinical context. These challenges suggest a requirement for external quality assessment or proficiency testing schemes that can inform participants about their performance in these areas when compared with other centres. 

There are proficiency testing programs that are geared toward clinical sensitivity or specificity by seeking to determine whether a disease can be detected versus other types of controls that are use to test sensitivity, selectivity, and most importantly, reproducibility and precision. With mass spectrometry, the controls are and should be no different than those used for other assays, with one interesting exception. Quality assurance materials prepared for MS/MS may not be useful in other assays that are less selective. The example is newborn screening where quality assurance/control QA/QC materials have a mixture of compounds present in the blood specimens. However, in less selective immunoassays, the mixture creates interferences. In addition, material is used to spike a blood sample is key and one should ensure there is no enzyme activity. We have encountered such a problem with a d/1 mixture of metabolites where one form was degraded in the prepared blood. 

Proficiency Testing of (Chemical) Analytical Laboratories .11 That protocol is recognised within the food sector of the European Community and also by the Codex Alimentarius Commission. The protocol makes the following recommendations about the organisation of proficiency testing, all of which are important in the food sector. 

Quality control of laboratories depends on the availability of CRMs, round-robin studies, intercomparisons and proficiency tests between methods and between laboratories. Of special importance is a full knowledge of the complex analytical process and the painstaking pursuit of the true value by defining all sources of errors and the application of an adequate error source budget. The application of Poisson and Bayesian statistics could have some advantage. 

More and more decisions based on chemical measurement are having global effects. Reference materials are important tools to obtain global comparability of results of chemical measurement. However, the use of validated analytical methods and the proof of personal skills by proficiency testing are other tools of the same rank (Fig. 1) [1],... 

In the U.S., proficiency testing has been held to be of utmost importance in accreditation programs and is typically mandated wherever it is possible to conduct. European systems of accreditation have been slower to include proficiency testing as an integral part of accreditation, but, in recent years, have begun to make greater use of proficiency testing. 

To conduct a proficiency test, a reference laboratory will prepare a quantity of material appropriate for distribution to all the laboratories under test. Requirements for the material will include that it is well characterized, and that it is sufficiently stable and homogeneous that no tested laboratory will be put at disadvantage by receiving a sample not representative of the lot. Further, the material should be typical of that of interest, and have constituents with concentrations within the ranges of interest. Additionally, it is important that concentration values be kept confidential during the period of the test, so that no participant will have an unfair advantage. 

An important objective of this project was to provide elements of method validation by estimating the bias, that is to say the difference between the measured value and the true value of measurands in samples. This can be underlined through a proficiency testing analysing either a spiked pure water or a matrix sample (drinking water), according to the diagram represented in Fig. 3. 

The ISO/IEC GUIDE 25 [1] stresses, in paragraphs 5.6 and 9.3, the importance of participation in proficiency testing programs or other interlaboratory comparisons, as appropriate and when suitable programs are available. This would imply that such activities are an important part of a laboratory s quality control procedures. 

According to ISO/IEC GUIDE 43-1 [2] traceability is The property of a result of a measurement or the value of a standard whereby it can be related to appropriate standards, generally international or national standards, through an unbroken chain of comparisons, all having stated uncertainties . It is thus quite clear that traceability is deemed important also in the field of proficiency testing. 

The model for an analysis and reporting strategy presented emphasizes the importance of a structured plan of work in combination with team s commitment, in the attempt to complete participation in the OPCW proficiency-testing scheme successfully. However, teamwork among laboratory staff may not be enough successful participation requires full support from management too. After all, management must understand that participation requires full devotion from the laboratory other tasks preferably have to wait for a later point in time. 

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