Proficiency testing schemes and other interlaboratory comparisons

Importance of the topic

Proficiency testing (PT) and other interlaboratory comparisons are central quality tools for laboratories performing routine and specialized measurements. They provide an independent external check on analytical performance, help validate methods and measurement systems, and support accreditation, regulatory compliance and trade confidence. By benchmarking laboratories against peers and reference values, PT schemes reveal systematic and random errors that internal controls alone may not detect, and they contribute to the overall reliability of environmental monitoring, public health testing, food safety and industrial quality control.

Objectives and overview of the study

This document outlines the types of interlaboratory comparisons, with emphasis on proficiency testing schemes as the predominant means to assess routine measurement quality. It clarifies different comparison objectives (certification trials, collaborative method validation, key comparisons) and highlights practical considerations for laboratories when selecting and interpreting PT schemes. The aim is to describe the role of PT in measurement quality, summarize advantages and limitations, and indicate uses in accreditation, education and regulatory contexts.

Methodology and practical elements of proficiency testing

• Types of comparisons: interlaboratory exercises range from certification trials used to assign reference material values, to collaborative trials for method validation, to key comparisons for top-level metrology.
• PT scheme design: schemes are defined by the materials used, analytes and concentration ranges, sample preparation (often processed for stability), delivery frequency and statistical evaluation protocols. No single protocol fits all needs, and providers vary in how results are assessed.
• Sample considerations: ideal PT samples mimic routine matrices and are homogeneous and stable. Practical constraints often require stabilization (e.g., chemical treatment, freeze-drying), which can affect commutability and interpretation of participant results.
• Evaluation metrics: schemes commonly use consensus or assigned values to judge participants, with statistical tools to quantify trueness and precision compared to peers or reference standards.

Main results and discussion

• Value of participation: PT provides objective, external evidence of routine analytical quality, enabling laboratories to compare results, identify problems and prioritize corrective actions.
• Educational and developmental role: many PT providers offer user meetings and feedback that support technical improvement and operator training. Virtual PT—using digital images or datasets—offers immediate feedback, scalability and repeat assessments.
• Impact on accreditation and regulation: PT outcomes are increasingly used by accreditation bodies and regulators to assess laboratory competence. Participation strengthens the case that procedures are fit for purpose and supports compliance with quality management requirements.
• Limitations and sources of uncertainty: variation in provider protocols, non-commutable or processed PT materials, and differing statistical treatment can lead to inconsistent judgments across schemes. Laboratories must therefore understand scheme design, sample preparation, and reporting conventions before relying on results for critical decisions.

Benefits and practical applications of proficiency testing

• Regular external benchmarking against peers and reference values.
• Objective evidence for internal quality assurance, accreditation dossiers and customer confidence.
• Comparative insight into method and instrument performance across a sector, region or country.
• Tool to detect systematic errors, evaluate method transfer and validate routine procedures beyond internal controls.

Selecting and using PT schemes: practical guidance

• Match scheme scope to routine practice: ensure test materials, analytes and concentration ranges reflect the laboratory’s workload.
• Assess sample commutability and note any processing used for stability; factor this into result interpretation.
• Check frequency and the level of detail provided in provider reports to ensure they support corrective action and documentation requirements.
• Prefer providers or schemes that follow recognized international guidance and, where possible, those accredited for PT provision.

Future trends and potential uses

• Digital and virtual PT: expanded use of digital images, simulated data and remote assessments will increase accessibility, allow high-frequency testing and rapid feedback loops.
• Harmonization and transparency: efforts to standardize evaluation protocols and reporting formats across providers will reduce inconsistent judgments and improve comparability.
• Advanced analytics: application of statistical learning and AI to large PT datasets can reveal systemic patterns, instrument- or method-specific biases, and opportunities for harmonization.
• Broader coverage: PT for emerging analytes and complex matrices will expand as analytical fields (e.g., genomics, nanomaterials, novel contaminants) evolve.
• Real-time quality monitoring: integration of PT-like external checks with continuous monitoring systems and laboratory information management systems will shorten corrective cycles.

Conclusion

Proficiency testing is a versatile, widely used external quality tool that complements method validation, internal quality control and accreditation processes. While PT schemes are not without limitations—sample commutability, protocol variability and provider differences can complicate interpretation—careful selection of appropriate schemes and informed use of results allow laboratories to substantially improve measurement reliability, demonstrate competence and support regulatory and trade requirements. Continued innovation in digital PT, harmonized evaluation and advanced data analysis will increase the value and reach of interlaboratory comparisons.

Reference

Produced by the Eurachem Proficiency Testing Working Group, Second English edition, July 2022