Demonstrating technical competence is a fundamental requirement for any testing or calibration laboratory. Customers, regulators, and accreditation bodies expect laboratories to produce results that are accurate, repeatable, and comparable with those of other competent laboratories. Two important tools used to establish and maintain this confidence are Inter-Laboratory Comparison (ILC) and Proficiency Testing (PT). While these terms are sometimes used interchangeably, they serve different purposes and operate at different levels of formality.
What Is Proficiency Testing (PT)?
Proficiency Testing is a structured, formal, and externally organized activity in which multiple laboratories test the same or similar samples under defined conditions. PT programs are typically conducted by independent third-party providers, ensuring impartiality and consistency. Each participating laboratory submits its test results, which are then statistically evaluated against pre-established performance criteria or assigned reference values.
The outcome of PT is objective and measurable. Laboratories receive performance scores that clearly indicate whether their results fall within acceptable limits. Because of this structured evaluation, PT is a mandatory requirement under ISO/IEC 17025 for laboratories to demonstrate ongoing technical competence. Accreditation bodies closely review PT participation and performance during assessments, making PT a critical element of compliance, risk control, and credibility.
What Is Inter-Laboratory Comparison (ILC)?
Inter-Laboratory Comparison is a broader and more flexible concept that includes PT but is not limited to it. ILCs can be formal or informal and may be organized directly between two or more laboratories without the involvement of a third-party provider. The objective of an ILC is often technical learning rather than compliance scoring.
ILCs are commonly used to compare test methods, validate new equipment or test setups, verify consistency between sites, investigate result deviations, or build confidence in measurements where formal PT schemes are not available. Unlike PT, ILCs may not involve statistical grading or pass/fail criteria. Instead, the focus is on understanding differences, improving methods, and aligning measurement practices.
Key Differences Between ILC and PT
The main distinction lies in purpose and structure. PT is formal, standardized, externally evaluated, and compliance-driven. ILC is flexible, collaborative, and improvement-driven. PT answers the question: Is the laboratory technically competent according to defined criteria? ILC answers: Do our methods and results align with others, and how can we improve them?
Why Laboratories Need Both
A strong laboratory quality system uses both PT and ILC strategically. PT satisfies accreditation and regulatory requirements, while ILC supports continuous improvement, technical development, and confidence-building. Together, they help laboratories move beyond minimum compliance toward sustained technical excellence.
Envitest’s Approach to ILC and PT
At Envitest Laboratories, PT participation is treated as a compliance baseline, while ILCs are leveraged as a learning tool. We actively use both to validate methods, strengthen measurement confidence, and continuously improve technical performance across testing domains.
Conclusion
Proficiency Testing is a formal subset of Inter-Laboratory Comparison, essential for accreditation and external assurance. Inter-Laboratory Comparisons, however, offer flexibility and depth that extend beyond mandatory requirements. Laboratories that understand and apply both effectively build not just compliance—but credibility, consistency, and long-term trust.
Quality is not proven once; it is demonstrated continuously.