Participation in proficiency testing (PT), is a key tool for demonstrating the technical competence of a laboratory. It allows performance to be compared with that of other laboratories, helps assess the validity of results and supports the detection of possible deviations before they affect the quality of the service provided.
However, a common question is: how often should a laboratory participate in proficiency testing?
The answer should not be limited to “once a year” or to a generic frequency applied to all activities. Participation in PT should form part of a planned, reviewed and justified strategy, taking into account the accreditation scope, the type of test, the associated risk, staff experience and other available quality control measures.
This approach is aligned with the principles of ISO/IEC 17025, which requires laboratories to monitor the validity of their results and to plan quality assurance activities in a way that is consistent with their technical scope. In this context, ISO/IEC 17043 is also a key reference for proficiency testing schemes and for the competence of the providers that organise them.
At SHAPYPRO, we understand proficiency testing as a practical tool to strengthen confidence in analytical results. For this reason, correctly defining the level and frequency of participation is essential so that laboratories can integrate PT into their quality system in a coherent and useful way.
What is meant by level of participation in PT
The level of participation refers to the specific activities within the laboratory’s scope that should be covered by proficiency testing.
It is not always feasible to participate in a different PT for every method, microorganism, matrix, product or parameter. In many cases, this would be difficult from an economic, logistical and technical point of view.
For this reason, the laboratory should analyse its scope and group together activities that can be considered technically equivalent. This grouping must be justified and based on objective criteria.
For example, in a microbiology laboratory, there may be different standards, matrices or microorganisms. The decision to group or separate activities will depend on factors such as:
- The method used.
- The microorganism analysed.
- The matrix or product under test.
- Sample preparation.
- Staff experience.
- Method validation or verification.
- The criticality of the result.
The objective is not to artificially reduce participation in PT, but to define coherent technical areas. In other words: it is not about participating less, but about participating with criteria.
What is meant by frequency of participation
The frequency of participation indicates how often the laboratory participates in proficiency testing for a given activity or technical area.
This frequency should not be decided in isolation. It must take into account the risk associated with the activity and the other quality control measures implemented by the laboratory.
An appropriate frequency can vary greatly between activities. Some areas may require more frequent participation, while others may be sufficiently controlled with a lower frequency, provided that there is a sound technical justification.
For example, an activity with a high sample volume, new staff, a complex methodology or critical results may require a higher frequency. In contrast, a stable activity, with low risk, experienced staff and robust internal controls, may require a lower frequency.
How to define a proficiency testing strategy
The first step in defining a proficiency testing participation strategy is to review the laboratory’s technical scope.
The laboratory must identify which activities it performs and how they relate to each other. To do this, it is useful to analyse three main elements:
- Measurement or testing process
The measurement process includes the method used, sample preparation, the equipment employed and the working conditions.
Two activities may appear similar in the scope, but require different competences if they use different methods or if sample preparation changes significantly.
- Characteristic or parameter evaluated
The characteristic is what is measured, identified or quantified. In microbiology, it may be a specific microorganism. In chemistry, it may be a compound or group of compounds. In other fields, it may be a physical property, a concentration or a functional response.
The laboratory should assess whether several parameters can be grouped within the same technical area or whether they should be treated separately.
- Product, matrix or sample
The matrix can have a direct impact on the result. Working with a liquid sample, a surface, a cosmetic product, a biocidal formulation or a complex matrix with interferences is not the same.
When matrices are technically equivalent and the method has been validated for them, grouping may be justified. When they are not, they should be treated as different areas.
Factors that influence the frequency of participation
The frequency of participation in PT should be defined using a risk-based approach. To do this, the laboratory may consider factors such as the following:
Workload
Activities that are performed very frequently may require regular participation in PT to confirm that performance remains stable.
The opposite may also be true: an activity that is only performed a few times a year may require specific monitoring, as lack of practice may increase the risk of error.
Method complexity
Complex methods, with several critical steps or demanding sample preparation, may require a higher frequency of participation.
In these cases, PT helps verify that the whole process is working correctly, not just an isolated part of the method.
Staff experience
Training, experience and the stability of the technical team are important factors. If there is staff turnover, new analysts join the team or task assignments change, it may be advisable to increase the frequency of participation.
Proficiency testing can also be used as a tool to verify the competence of different analysts within the laboratory.
Changes in equipment, methods or procedures
When new equipment is introduced, a method is modified, a procedure is updated or a critical test condition changes, it may be necessary to review the PT strategy.
The laboratory should assess whether the defined frequency remains appropriate or whether participation in an additional exercise is advisable to confirm performance.
Importance of the final result
Not all results have the same impact. Some tests may have relevant regulatory, commercial, health or legal consequences.
The greater the importance of the result, the higher the level of confidence required from the quality control system.
Availability of other quality controls
Participation in PT is not the only mechanism for controlling the validity of results. It can be complemented by internal controls, reference materials, blind samples, internal comparisons, periodic checks and trend reviews.
When these controls are robust, documented and effective, they can help justify the defined frequency. When they are limited, participation in PT becomes even more important.
Frequency should not be seen as an isolated requirement
One of the most common mistakes is to treat participation in PT as a one-off action to comply with an audit.
A proficiency test should not be seen as a simple annual registration. It should form part of an overall quality assurance strategy.
This involves:
- Planning participation in advance.
- Selecting programmes that are appropriate for the technical scope.
- Reviewing the results obtained.
- Investigating unsatisfactory results.
- Applying corrective actions when necessary.
- Evaluating trends over time.
- Reviewing the strategy during management review.
Participation in PT has value when its results are used for improvement. If the laboratory simply files the report away and hopes nobody asks too many questions, it becomes a purely administrative exercise with very limited technical value.
How to justify a PT participation strategy
A well-defined PT strategy must be documented. This is not only a matter of good technical practice, but also of demonstrating, in line with ISO/IEC 17025, that the laboratory systematically plans and reviews how it ensures the validity of its results.
A good justification may include:
- The relationship between the selected programmes and the accredited scope.
- Criteria used to group technical areas.
- Frequency assigned to each area.
- Risk assessment.
- Complementary quality controls.
- History of results.
- Recent technical changes.
- Annual review of the strategy.
- Actions taken in response to unsatisfactory results.
This documentation helps the laboratory demonstrate that its participation is not arbitrary, but part of coherent technical planning.
Proficiency testing in biocidal efficacy laboratories
In the field of biocidal efficacy, participation in proficiency testing is particularly important. Laboratories work with standardised methods, specific microorganisms and test conditions that must remain under control.
The results may be related to the evaluation of the efficacy of disinfectants, antiseptics or other products with antimicrobial activity. Therefore, it is essential for the laboratory to demonstrate that its results are comparable, reliable and technically consistent.
In this context, SHAPYPRO’s programmes allow laboratories to assess their performance in tests related to European efficacy standards, using microorganisms and conditions that are relevant to their activity.
Regular participation in these programmes can help to:
- Confirm the technical competence of the laboratory.
- Detect deviations in the method.
- Compare performance with other participants.
- Strengthen confidence in the results.
- Provide objective evidence within the quality system.
- Prepare audits and internal reviews with greater confidence.
2026 agenda: ongoing programmes
As part of SHAPYPRO’s planning for 2026, several proficiency testing exercises have already been scheduled. To view the full calendar, the 2026 agenda can be downloaded at the following link:
https://shapypro.com/2026-agenda/
The programmes currently in progress are:
- EN1656 – P. aeruginosa
- EN1657 – C. albicans
- EN1276 – S. aureus
- EN1650 – A. brasiliensis
- EN13704 – B. cereus
Integrating this type of calendar into the PT participation strategy is important because frequency is not defined only in abstract terms. It also depends on planning ahead, allocating resources and making use of available programmes in a way that is consistent with the laboratory’s areas of technical competence.
For many laboratories, having an annual agenda makes it easier to organise participation, distribute workload and ensure that the relevant technical areas are covered within the planned period.
Reviewing the PT strategy: an ongoing task
The proficiency testing participation strategy should not remain unchanged for years without review.
The laboratory should review it periodically, especially when relevant changes occur. Examples include:
- Introduction of new methods.
- Extension of the accreditation scope.
- Changes in technical staff.
- Unsatisfactory results in previous PT exercises.
- Changes in workload frequency.
- New requirements from clients or authorities.
- Changes in equipment or facilities.
- Availability of new proficiency testing programmes.
This review allows the frequency of participation to be adjusted to the laboratory’s actual situation. It also helps avoid two undesirable extremes: insufficient participation or participation without a clear strategy.
What to do in the event of an unsatisfactory result
An unsatisfactory result in PT should not be seen only as a problem. It can also be an opportunity to identify weaknesses and strengthen the quality system.
When a result falls outside the established criteria, the laboratory must analyse the cause. The investigation may include a review of:
- Sample preparation.
- Test conditions.
- Strains or materials used.
- Equipment and calibrations.
- Calculations performed.
- Technical records.
- Staff training.
- Interpretation of programme instructions.
Afterwards, appropriate corrective actions should be defined and their effectiveness verified. In some cases, it may be advisable to participate in a new exercise to confirm that the problem has been resolved.
The key is to treat the result as a source of technical information, not as a simple administrative incident.
Conclusion
Defining the level and frequency of participation in proficiency testing requires technical analysis, not an automatic response.
Each laboratory must review its scope, identify its areas of competence, assess the associated risks and select appropriate programmes to demonstrate the validity of its results.
A robust PT strategy should be proportionate, planned, documented and reviewed periodically. It should also be integrated into the laboratory’s quality system, together with other internal controls and assurance tools.
At SHAPYPRO, we work to offer proficiency testing programmes that help laboratories assess their performance, strengthen their technical competence and plan their participation in a way that is consistent with their real needs.
Participation in PT is not only a requirement within a quality system. It is a tool for improvement, comparison, risk detection and confidence in results. And in a laboratory, confidence should never be improvised.