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Why participate in a PT scheme?

The International Organisation for Standardization defines proficiency testing (PT) as “the evaluation of participant performance against pre-established criteria, by means of inter-laboratory comparisons.” Simply put, participating in a PT scheme provides a laboratory with objective evidence to monitor competence, in order to improve performance and give both the laboratory and its customers confidence in their ability to perform specific measurements.


It’s important to note that PT is just one of a number of tools available to laboratories as part of a quality management system. To establish and maintain its measurement system, a laboratory will need to validate and verify its methods, calibrate its instruments, ensure the competence of its staff, and put in place internal quality control. These ‘input measures’ are best managed with the use of reference materials.


However, it's also essential for a laboratory to assess the quality of its measurement results, i.e. the ‘output’, via an independent and external comparison with other laboratories. Participation in a PT scheme provides the mechanism for a laboratory to do just this.


Role of a PT scheme in quality assurance


In order to understand the role of a PT scheme in quality assurance it’s necessary to familiarise oneself with the three-phase measurement cycle, illustrated in the graphic below. There are many different PT scheme designs and structures, and different schemes may address individual aspects or phases of the measurement cycle, or address the cycle in its entirety.


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The Pre-Measurement Phase consists of the identification of a problem to be solved. Once the problem has been identified, a decision is reached between the client and the laboratory as to what measurements are required to address the issue. Suitable samples are then collected from which to undertake the necessary measurements.


Participation in a PT scheme can assess this decision making process as well as the actual sampling. To take the LGC AXIO toy testing PT scheme (TOYTEST) as an example, participating laboratories assess the toys they receive from LGC against national/international standards to decide on what tests need to be carried out. During the Measurement Phase, the laboratory makes necessary measurements on the samples using validated measurement procedures. This testing may consist of quantitative or qualitative analysis. This is perhaps the phase in which PT has been more traditionally used by laboratories to assess and monitor their performance.


Any measurements made are to address specific issues, and thus decisions are required about the measurement results. This is the Post-Measurement Phase, when the results are interpreted by the laboratory or the client. 


Again, PT can play an important role is assessing the quality of the interpretations made. To take the LGC AXIO forensic toxicology scheme (QUARTZ) as an example, the test materials are provided along with a case study, based on which the laboratory provides an interpretation of the measurements they make. This is an example of a PT scheme that covers both the measurement and post-measurement phases.


A multitude of benefits


Participating in a PT scheme offers a laboratory an efficient means of identifying opportunities for systemic and continuous improvements.


Brian Brookman is LGC’s Chief Scientific Officer for Proficiency Testing, with over 25 years experience in the field of analytical quality. “The ability to pinpoint measurement problems – either by comparing measurement methods/instruments used across different locations, or comparing two or more methods/instruments used within a single laboratory – means that, whether a client is operating hundreds of laboratories or just the one, participating in a PT scheme is sure to add value,” he says.


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PT’s utility extends beyond methodology and equipment, of course – it also functions as a means of assessing the capabilities of individual analysts, thereby helping laboratory managers to identify inconsistencies in the application of a particular measurement procedure, and figure out where additional training may be needed. “Whilst analysts may be proficient at detecting routine contaminants, the significant majority of measurement errors happen when less routine samples are received by the laboratory,” says Brookman. “PT helps expose analysts to unusual or atypical challenges, to ensure they can recognise and respond to concerns outside of the routine.”


The relationship between participants of a PT scheme and the PT scheme’s providers should be a two-way street. Feedback provided by participants regarding issues encountered during participation in the PT scheme is utilised by the PT provider to develop further and improve the PT schemes provided. Equally, participants should treat the PT test materials as they would routine  samples and review all the information provided to them in the PT report, with an attitude of openness and honesty, in order to identify and implement necessary improvements.


There has long been a debate about whether PT providers are best classified as educators or enforcers – as ‘teachers’ or ‘police officers’. The truth lies somewhere in between these two descriptions. “Like any good educational system, a degree of regulatory oversight is necessary for a PT scheme to flourish,” says Brookman. “But it’s important to reflect on the necessity of an honest assessment of a laboratory’s performance insofar as this pertains to its output – without sufficient monitoring and feedback, the end users of all kinds of products, from children’s toys to ready meals, could be put at risk.”


A new vision for PT


LGC is proud to announce the launch of our rebranded proficiency testing offering to the market: AXIO Proficiency Testing. Drawing on forty years of PT experience, AXIO Proficiency Testing is built on the pillars of Leadership, Influence, Partnership, Evolution and Trust, offering our customers ‘Confidence in Your Continuous Improvement’ with our PT schemes, test materials, performance reports and customer service. The quality of our PT provision is well reflected through our scope of accreditation to ISO/IEC 17043.

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