Proficiency Testing – What It Really Tells You About Your Laboratory

For many laboratories, proficiency testing (PT) is a routine part of maintaining accreditation. A PT sample arrives, testing is completed, the results are submitted, and the laboratory waits to see whether its performance is satisfactory.

If the results are acceptable, the PT study is closed and everyone moves on to the next project.

While this approach satisfies part of the requirement, it also misses one of the greatest benefits of proficiency testing.

PT is much more than an accreditation requirement.

When used effectively, it becomes one of the most valuable tools for evaluating laboratory performance, identifying opportunities for improvement, and building confidence in reported results.

Why Proficiency Testing Matters

Laboratories generate data that customers use to make important decisions.

Depending on the type of laboratory, those decisions may involve:

• Environmental compliance
• Product quality
• Public health
• Industrial operations
• Research and development

Customers trust that reported results are technically valid.

Proficiency testing provides independent evidence that the laboratory can produce reliable results using its normal methods, equipment, and personnel.

For this reason, participation in PT is an important element of both ISO/IEC 17025 and, for many environmental laboratories, TNI 2016.

Passing a PT Study Is Not the Only Goal

One observation I’ve made over the years is that many laboratories focus almost exclusively on one question:

“Did we pass?”

Of course, satisfactory performance is important.

However, even successful PT results can provide valuable information.

For example:

• Were the results close to the assigned value or just within the acceptance limits?
• Have similar trends appeared in previous PT studies?
• Did different analysts produce consistent results?
• Were there any unusual observations during testing?

Looking beyond a simple pass/fail outcome often provides valuable insight into laboratory performance.

A PT study should be viewed as an opportunity to learn—not simply as another accreditation requirement.

PT Results Should Lead to Questions

Whether the outcome is satisfactory or unsatisfactory, every PT study presents an opportunity for evaluation.

Questions worth asking include:

• Were all quality control checks acceptable?
• Did the analyst encounter unexpected challenges?
• Were calculations independently verified?
• Could equipment performance have influenced the results?
• Are similar trends appearing in routine quality control data?

These discussions help laboratories understand not only what happened, but also why it happened.

Unsatisfactory Results Are Not Failures

Receiving an unsatisfactory PT result is never pleasant.

However, it should not automatically be viewed as evidence of poor laboratory performance.

Even well-managed laboratories occasionally experience unexpected PT results.

The important question is how the laboratory responds.

An effective investigation should consider factors such as:

• Sample preparation
• Instrument performance
• Calibration
• Analyst technique
• Calculations
• Data transcription
• Method application

The objective is not simply to identify a mistake.

It is to determine whether the issue could also affect routine customer samples and whether improvements are necessary.

A thoughtful investigation often strengthens the laboratory’s overall quality system.

PT Is One Part of Demonstrating Competence

Proficiency testing is an important tool, but it is not the only evidence of laboratory competence.

Strong laboratories also rely on:

• Quality control samples
• Certified reference materials
• Equipment calibration
• Method validation or verification
• Internal audits
• Competency evaluations
• Data review processes

Together, these activities provide confidence that reported results are technically valid.

No single quality tool should be viewed in isolation.

One Observation from Internal Audits

One characteristic I’ve consistently observed in high-performing laboratories is that they treat PT results as opportunities for continual improvement rather than simply accreditation records.

Management discusses trends.

Technical staff review lessons learned.

Corrective actions are implemented when appropriate.

Most importantly, PT results become part of broader conversations about laboratory quality rather than isolated reports filed away after submission.

This approach helps create a culture where learning is valued as much as compliance.

Questions to Consider

Take a moment to reflect on your own laboratory.

• How are PT results discussed after each study?
• Do you analyze trends over time or focus only on pass/fail outcomes?
• Could PT data be used to improve training, methods, or quality control?
• Are lessons learned shared with the entire laboratory?

These simple questions often reveal opportunities to strengthen both technical competence and the laboratory management system.

Key Takeaway

The true value of proficiency testing is not demonstrated by receiving a satisfactory score.

It is demonstrated by how effectively the laboratory uses PT results to evaluate performance, identify improvement opportunities, and continually strengthen confidence in its data.

Conclusion

Proficiency testing is much more than an accreditation requirement.

It provides laboratories with independent evidence of technical competence while also creating valuable opportunities to learn, improve, and build confidence in reported results.

Laboratories that treat PT as part of their continual improvement process—not simply as a compliance activity—are often better prepared for accreditation assessments and better positioned to deliver reliable results to their customers.