Proficiency testing (PT) is an important approach to ensure the lab delivers accurate and high-quality results to key stakeholders. PT is often required under different types of accredited quality programs, but is valuable to any lab delivering quantitative testing results.
Unsatisfactory assessments
The most obvious common PT challenge is the so-called “unsatisfactory” assessment. This is a challenge on many levels, not just for the laboratory but for the analyst whose job performance review is under scrutiny and the quality manager who must defend this to company directors, their accreditation body, customers, and potential clients. No one likes to be in that position. However, this must be taken in context, which in turn can mitigate these business pressures. What is the magnitude of that unsatisfactory score? Is it a one-off error? More importantly, what is the long-term trend of performance scores, and do these meet the expectation of a normal distribution and an absence of bias?
Common errors
The most common error that we see is one of calculation, evidenced by a result that is almost exactly 2x, 10x, or 100x out. Was that pipette set to 100 µl or 200 µl? Was the formula in the spreadsheet set to 0.1 or 0.01? Was the analytical balance tared to one disposable weighing boat, and did the next measurement have two weighing boats stuck together without taring the balance? These are all easily traceable and explainable, if slightly embarrassing for the person owning up to it. Or to put a positive spin on it, it’s an opportunity for learning and improvement.
Importance of training
Some controls are more nuanced and might be slightly less obvious, especially in a high-pressure business environment. It’s common practice for new staff to be trained by existing staff, but if the laboratory has high staff turnover, how experienced are those existing staff? Are we at risk of propagating a process that is itself in error? When was the last time that someone performed the method with the SOP in front of them? One thing I always say to new staff is to check the SOP and let me know if you’ve been trained differently. There is a very real risk of someone previously taking a shortcut to fix a method problem, which then becomes embedded by word of mouth, and no one has checked the SOP.
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Requirements of the proficiency testing provider
Two further considerations for “unsatisfactory” performance are the nature of the interlaboratory comparison and potential for method-dependency in the results. If the PT provider is accredited to ISO 17043, then homogeneity and stability of the PT samples should not be a major consideration; these will already be under scrutiny by the PT provider, as required by the ISO 17043 standard. The standard also requires the PT provider to consider method-dependency. These (homogeneity, stability, method) are common challenges to the PT provider, but in the majority of cases distract from internal investigations within the participant laboratory. A PT is an interlaboratory comparison, and the majority of PTs are also inter-method comparisons. Any method dependency (or any other trend) should be evident within the PT data and explored by the PT provider. Most of the time, there are no observable (i.e., statistically significant) dependencies that would impact a participating lab.
Designing an effective PT program
Taking part in a PT tends to be a short-term activity for those directly involved; receive sample, do the analysis, submit result, receive assessment report. It does pay, however, to consider the longer-term cycle of PT participation and how that benefits both accreditation and the needs of the laboratory (whether that is economic, resource management, or business development). Primarily, PT is a measure of laboratory performance and should be targeted to those analyses that are being undertaken routinely in established processes. Crisis management demands that a new method be validated and implemented very quickly, and PT can meet that demand, but this is unusual. It’s the everyday laboratory processes that are generally subjected to PT. This, in turn, raises a number of questions. What frequency of PT matches the frequency of routine sample analysis? What is the cycle of accreditation for that method? Are you using PT as verification of training for new staff? What is the annual program cycle of your chosen PT provider, and is that aligned with your annual cycle? If there is no exact match of a PT, what is the next best PT available, and what does the PT provider advise?
Addressing PT challenges
Finally, there is plenty of support for laboratories to help address their PT challenges. This is unlikely to be from the accreditation body, however. They generally have to remain neutral and not provide a consultancy service. PT providers are a good starting point, but also the networks that PT providers are involved in, especially internationally. The Eurachem and ILAC networks, in particular, provide guidance documentation for both PT providers and users of PT. The IUPAC Harmonized Protocol of 2006 is not only still relevant but largely unsurpassed as the international guidance document for all things PT.
Ultimately, it’s the responsibility of the participant laboratories to make the most of the PT opportunities and use that PT to help themselves. Perhaps the biggest challenge for laboratories is actually inward-facing, to use the PT results as platforms for learning and improving their standard testing methods.
