Selecting the right proficiency testing scheme for my laboratory

Significance of the topic

Proficiency testing (PT) participation is a cornerstone of laboratory quality assurance, providing independent verification of analytical performance, comparability of results and confidence for customers and regulators. Choosing the most appropriate PT schemes reduces unnecessary cost and effort, targets meaningful assessments for the laboratory's actual workload, and supports accreditation and regulatory compliance.

Objectives and overview of the guidance

This leaflet aims to help laboratories select PT schemes that best match their testing scope. It outlines key questions and decision criteria so laboratories can prioritise schemes that are relevant, statistically robust and aligned with customer, accreditation and regulatory expectations. The guidance highlights areas to evaluate: test parameters, PT provider strategies, performance evaluation methods, trustworthiness of providers and communication quality.

Parameters included in the PT

Assess whether PT items mirror routine sample characteristics in terms of matrix, analyte identity and concentration ranges. If PT materials differ substantially from routine samples, the chosen scheme may only assess parts of the analytical process (e.g. sequencing vs. whole-test competence) or may be inappropriate. Examples from the guidance illustrate this: PT for drinking water contaminants will typically present much lower concentration ranges than industrial waste samples; DNA PTs may supply either intact tissue or purified extracts, changing which steps of the workflow are challenged. Laboratories should therefore decide whether to participate with clear understanding of the limitations or to select alternative schemes better aligned with their matrices and analyte ranges.

Strategies for data collection and analysis

Laboratories should review the PT provider’s statistical design and logistical procedures to ensure they fit the lab’s needs. Relevant factors include:

• Description of statistical design and performance scoring methods
• Number of test items and required replicates
• Data submission channels and formats (web portal, email, fax)
• Procedures for comparing results across different measurement procedures
• Participant population size and diversity, including how many use the same method
• Methods and criteria for performance assessment

In cases where operationally defined methods are used (example: fat determination in various matrices using distinct extraction procedures), it is essential that the PT scheme recognises such method-dependent biases or treats each method separately in the evaluation so that comparisons are fair and meaningful.

Evaluation of performance

Verify that the PT provider clearly documents the performance assessment method (for example, z-scores), and that the laboratory understands how those metrics are derived and applied. Consider whether measurement uncertainty reported by the laboratory will be accommodated in the provider’s evaluation. Additionally, ensure the provider’s acceptability criteria align with the laboratory’s role: confirmatory testing may justify stricter performance thresholds than screening-level analyses.

Trust in the PT provider

Assess the provider’s competence and suitability by considering:

• Compliance with ISO/IEC 17043 and related accreditation
• Provider experience and track record
• Reliability and traceability of assigned values for PT materials
• Fitness-for-purpose of performance criteria and evaluation approaches

Accreditation and transparent documentation of value assignment methods are strong indicators of provider quality.

Communication

Effective two-way communication is crucial. Laboratories should evaluate the provider’s:

• Language and clarity of documentation
• Timeliness and completeness of reports
• Accessibility and responsiveness of support
• Opportunities for engagement (e.g. user meetings) and flexibility to accommodate customer needs

Good communication reduces misunderstandings about scope, deadlines and interpretation of results.

Main results and discussion (practical implications)

The guidance synthesises practical decision points rather than experimental results. Key implications for laboratories are:

• Choose PT schemes whose matrices, analyte forms and concentration ranges exercise the same steps and challenges as routine testing
• Confirm the PT provider’s statistical approach and participant mix are suitable for fair comparisons, especially when multiple operationally different methods exist
• Ensure performance scoring methods are transparent and compatible with declared measurement uncertainty and regulatory expectations
• Prefer providers with recognised accreditation and clear documentation of assigned values and evaluation criteria

Applying these criteria helps laboratories obtain meaningful proficiency evidence, avoid misleading assessments and prioritise PT participation cost-effectively.

Benefits and practical uses of the approach

Selecting PT schemes using the described criteria delivers multiple practical benefits:

• More relevant assessment of laboratory competence for routine work
• Improved alignment with accreditation and regulatory requirements
• Efficient allocation of resources by avoiding unsuitable or redundant schemes
• Enhanced ability to interpret PT outcomes and to implement corrective actions where needed

Future trends and potential applications

Anticipated developments that will influence PT selection and design include:

• Greater use of method-specific subschemes to address operationally defined procedures and emerging techniques
• Increased transparency and sophistication in statistical evaluation, including approaches that integrate participant-reported measurement uncertainty
• Digitalisation of data submission, reporting and interactive result analysis platforms
• Growth in tailored and specialist PT programmes for niche matrices or high-complexity analyses (e.g. molecular methods, contaminants at ultra-trace levels)

These trends will improve the relevance and utility of PT for diverse laboratory types but will require laboratories to engage more actively with providers on scheme design and reporting expectations.

Conclusion

Thoughtful selection of PT schemes is essential to obtain meaningful, cost-effective external verification of laboratory performance. Laboratories should systematically evaluate PT parameters, statistical design, performance evaluation methods, provider competence and communication quality. Aligning scheme choice with routine practice, accreditation needs and regulatory obligations maximises the value of PT participation and supports continual improvement.

References

The summary is based on guidance from the Eurachem Proficiency Testing Working Group and cites the Eurachem Guide: Selection, Use and Interpretation of Proficiency Testing (3rd ed., 2021). Further information on PT providers and schemes is available from national accreditation bodies and international PT information services.