Pre- and post-analytical proficiency testing

Importance of the topic

Routine chemical and microbiological analyses comprise multiple stages beyond the analytical measurement itself: selection of procedure, sampling, sample preparation, measurement, result calculation, uncertainty estimation and reporting. Steps that occur before and after the instrument measurement—pre- and post-analytical processes—can introduce substantial variability and uncertainty that affect decisions based on laboratory results. Proficiency testing (PT) and external quality assessment (EQA) schemes that explicitly include pre- and post-analytical elements therefore play a critical role in assessing and improving total process quality, harmonising practice across laboratories, and informing accreditation and regulatory frameworks.

Objectives and overview of the document

The primary aim is to illustrate the value and practical design of PT/EQA schemes that incorporate pre- and post-analytical aspects. The document provides examples showing how such schemes can reveal problems not detectable by conventional proficiency tests that focus solely on measurement performance. It also intends to inspire PT providers to extend their external quality control activities to include scenario-based and interpretative assessments that cover the full laboratory process.

Methodology and practical design of pre- and post-analytical PT/EQA

• Concept: Design PT/EQA exercises that simulate real-life sample contexts and workflow choices so participants must apply pre-analytical decisions (e.g., sampling strategy, analyte selection, sample handling) and post-analytical actions (e.g., result interpretation, reporting, communication to stakeholders).
• Assessment: Use expert panels or predefined model answers to evaluate both technical outputs (results and uncertainties) and non-technical outputs (interpretation, communication, adherence to standards and legislation).
• Reporting: Provide feedback that compares participant responses with provider recommendations, highlights deviations in procedure or interpretation, and gives educational commentary to support improvement.
• Examples used to demonstrate design: clinical interpretation exercises, microbiology sampling requests, toy safety testing against standards, and drinking-water compliance assessments close to regulatory limits.

Main results and discussion

• Pre- and post-analytical schemes reveal errors and variability not captured by measurement-focused PT. Examples include inconsistent adherence to guidance, divergent sample preparation choices, and variable interpretation of results.
• Scenario-based exercises (clinical case histories, food-poisoning simulations) expose differences in decision-making, organisms tested, or public-health reporting procedures, enabling assessment of the total testing pathway including communication to external stakeholders.
• Standard-based testing exercises (toy safety using EN 71 clauses) test laboratories’ ability to select applicable clauses and perform the corresponding tests, thereby identifying gaps in understanding of normative requirements.
• Regulatory-type exercises (drinking-water samples near parametric limits) assess participants’ abilities to report results with uncertainties and to provide pass/fail recommendations consistent with legislation, supporting regulator–laboratory dialogue.
• By documenting common deviations and patterns, pre/post PT/EQA supports harmonisation: it provides evidence for updating guidelines, improving training, and refining national or international standards.

Benefits and practical applications

• Quality assurance across the entire laboratory process: helps ensure that sampling, preparation, measurement, interpretation and reporting are all fit for purpose.
• Support for accreditation: aligns with accreditation requirements (e.g., ISO 15189) that call for EQA to address the entire testing process, including pre- and post-examination procedures.
• Training and competence assessment: scenario-based PT serves as an educational tool to expose weaknesses in decision-making and interpretation.
• Harmonisation and guideline development: aggregated results identify common issues that can inform updates to SOPs, standards and best-practice guidance.
• Regulatory engagement: PT data from post-analytical exercises can be used to inform regulators about laboratory practices and potential needs for regulatory clarification or intervention.

Used instrumentation

The source document does not prescribe specific analytical instruments. The focus is on exercise design, decision-making and conformity assessment rather than on the technical instrumentation used for measurements. Individual PT schemes would specify required analytical methods or instruments where relevant to the tested clauses or analytes.

Future trends and potential applications

• Expansion of scenario-based PT across sectors: greater adoption in clinical chemistry, microbiology, environmental and consumer-product testing to evaluate the full testing pathway.
• Digital and hybrid exercises: use of electronic case simulations, virtual datasets and remote submission systems to simulate pre- and post-analytical decisions at scale.
• Metadata and interoperability: inclusion of richer pre-analytical metadata (sampling conditions, chain-of-custody, handling times) to enable root-cause analysis and benchmarking.
• Advanced analytics for feedback: use of statistical and machine-learning tools to classify common error modes, cluster participant behaviours, and tailor educational feedback.
• Regulatory integration: stronger links between PT outcomes and regulatory bodies to inform surveillance priorities and harmonise interpretation of legislative limits.
• Standardisation of exercise design: development of guidance documents and consensus templates for pre/post PT to improve comparability across providers.

Conclusion

Pre- and post-analytical PT/EQA fills a critical gap in quality assurance by assessing the non-measurement parts of the laboratory workflow that strongly influence the value of reported results. Well-designed schemes provide actionable feedback, support accreditation requirements, improve harmonisation across laboratories, and enable better regulatory engagement. PT providers are encouraged to develop scenario-based and interpretative exercises to drive improvements in the total testing process and to support ongoing professional education.

References

• ISO 15189 Medical laboratories — Requirements for quality and competence.
• Directive 98/83/EC on the quality of water intended for human consumption.
• Eurachem Proficiency Testing Working Group, Second English edition, July 2022.
• EPTIS (European Proficiency Testing Information System) — information source for PT providers and schemes.