Decoding Quality: A Guide for Interpreting Proficiency Testing Results Effectively

Proficiency testing or PT is a critical tool for laboratories to ensure the quality and reliability of their analytical processes. However, the real value of PT lies not just in participation but in being able to effectively interpret or decode the PT results. PT is not about “passing” or “failing” a measurement; it is about learning from the results.

Here’s how you can understand your PT results:

Understanding the basics:

Before interpreting, ensure you’re familiar with key statistical terms used in PT reports, such as z-scores and standard deviations. This is a crucial step for accurate interpretation.

Review Your Performance Indicators:

Most PT schemes use performance indicators like z-scores or En numbers. For z-scores, generally:

|z| ≤ 2 is considered satisfactory

2 < |z| < 3 is questionable

|z| ≥ 3 is unsatisfactory

Look Beyond Pass/Fail:

While meeting the acceptable criteria is important, don’t stop there. Even satisfactory results can reveal trends or improvement opportunities. Analyze patterns across multiple PT rounds and different analytes to gain comprehensive insights.

Comparative Analysis:

Compare your results with those of other participants given in the report. This allows you to assess your performance relative to similar laboratories. Consistent deviations need investigation.

Monitoring performance over time:

Track your performance over time to identify any drifts or shifts in your analytical processes. This view can reveal subtle issues before they become significant problems.

Investigations of Unsatisfactory or Questionable Results:

All laboratories will occasionally have unsatisfactory or questionable PT results. When this occurs, the laboratory should clearly identify and document them. The key issue is that unsatisfactory performance needs to be investigated and trends should be examined.

Correlate with your internal Quality Control Checks:

Compare your PT results with your internal quality control data. Discrepancies between the two might indicate issues with your quality control processes or highlight the need for more frequent or rigorous internal checks.

Holistic Approach:

Interpret PT results within the broader context of your quality management system. Consider how these outcomes align with your overall quality objectives and what they reveal about your laboratory’s strengths and areas for development.

Strategic Corrective Actions:

When corrective measures are necessary, approach them strategically. Avoid hasty changes that might disrupt well-functioning processes. Instead, implement a structured approach to improvements, ensuring each change is verified and validated.

Communicate results effectively:

Share PT results and their implications with all relevant staff. This promotes a culture of quality and ensures understanding throughout the organization.

Documentation of the Interpretation Process:

Maintain clear records of how PT results were interpreted, including any discussions, decisions, and actions taken. This documentation is crucial for traceability and can be valuable for future reference or during audits.

PT and Regulatory Compliance:

Proficiency testing is often a key requirement for maintaining laboratory accreditation and meeting regulatory standards. Effective interpretation and use of PT results demonstrate your lab’s commitment to quality and continuous improvement to accreditation bodies and regulators.

Remember, PT participation and results are tools for continuous improvement, not a tick-mark exercise. Use insights gained from PT to refine processes, enhance training, and ultimately improve the quality of your laboratory’s output.

Are you extracting maximum value from your PT participation? Consider implementing these strategies in your next PT round and observe the positive impact on your laboratory’s performance and quality assurance processes.