Ensuring the Validity of Results (ISO 17025 Clause 7.7)

Introduction

A laboratory must have a procedure for monitoring the validity of its results. This monitoring must be planned and reviewed.

Internal Monitoring (7.7.1)

This involves regular checks within the lab. Examples include:

• Reference materials: Using RMs or CRMs as check standards.
• Retaining samples: Re-testing retained items.
• Intermediate checks: Verifying equipment status between calibrations.
• Blank checks: Testing blanks to check for contamination.
• Replicate tests: Testing the same sample multiple times (repeatability).
• Blind tests: Testing samples where the analyst doesn’t know the expected value.

External Monitoring (7.7.2)

This involves comparing your results with other laboratories.

• Proficiency Testing (PT): Participation in organized interlaboratory comparisons.
• Interlaboratory Comparisons (ILC): Organizing a comparison with one or more other capable labs (if commercial PT is not available).

Analyzing the Data (7.7.3)

Data from monitoring activities must be analyzed.

• Control Charts: Use Shewhart charts (X-bar, R charts) to detect trends or shifts.
• Action Limits: Define criteria for when to take action (e.g., if a result is > 3 SD from the mean).