Proficiency Testing vs Internal Quality Control: Why Many ISO/IEC 17025 Laboratories Get This Wrong

Understanding the critical differences between proficiency testing and internal quality control in ISO/IEC 17025 laboratories.

By Ashley Dennis • Laboratory Quality Systems Expert
Published 2026
Category: Laboratory Accreditation | ISO/IEC 17025
Reading time: ~4 minutes

Introduction

Laboratories operating under ISO/IEC 17025 must demonstrate that their testing activities produce technically valid and reliable results. Two critical tools used to monitor analytical performance are proficiency testing and internal quality control.

Although these processes both evaluate laboratory performance, they serve very different purposes. Many laboratories mistakenly treat proficiency testing and internal quality control as interchangeable activities. This misunderstanding can lead to gaps in quality system implementation and potential nonconformities during accreditation assessments.

Understanding the distinct roles of proficiency testing and internal quality control helps laboratories maintain compliance with ISO/IEC 17025 and ensures confidence in reported analytical results.

What Is Proficiency Testing?

Proficiency testing evaluates a laboratory’s analytical performance by comparing its test results with those of other laboratories analyzing the same sample.

Proficiency testing programs are typically organized by independent providers that distribute test samples to participating laboratories. After performing the analysis, laboratories submit their results to the provider for statistical evaluation.

The results allow laboratories to determine how their analytical performance compares with other laboratories performing the same test method.

Purpose of Proficiency Testing

Participation in proficiency testing programs helps laboratories demonstrate technical competence and verify that analytical methods are producing accurate results.

• compare analytical results with other laboratories
• evaluate method performance
• identify potential analytical issues
• demonstrate competence to accreditation bodies

ISO/IEC 17025 requires laboratories to monitor the validity of their results, and proficiency testing is one of the primary ways laboratories demonstrate this requirement.

What Is Internal Quality Control?

Internal quality control refers to routine monitoring activities performed within the laboratory to ensure that analytical processes remain stable and reliable during daily testing operations.

These activities help laboratories detect analytical problems before test results are reported.

• analysis of control samples
• use of reference materials
• calibration verification checks
• monitoring instrument performance

Key Differences Between Proficiency Testing and Quality Control

Proficiency testing

• external evaluation of laboratory performance
• comparison with other laboratories
• performed periodically
• typically organized by independent providers

Internal quality control

• routine monitoring during testing
• evaluates day-to-day analytical performance
• performed using internal control materials
• detects issues before results are reported

Why Both Are Necessary

ISO/IEC 17025 laboratories rely on both proficiency testing and internal quality control to demonstrate the reliability of their analytical results.

Internal quality control provides continuous monitoring of laboratory performance, while proficiency testing offers periodic independent evaluation of analytical accuracy.

Together, these activities help laboratories identify issues early and maintain confidence in their testing results.

Conclusion

Proficiency testing and internal quality control serve distinct but complementary roles within laboratory quality management systems. While proficiency testing evaluates laboratory performance relative to other laboratories, internal quality control ensures that analytical processes remain stable during routine operations.

Understanding these differences helps laboratories maintain compliance with ISO/IEC 17025 and strengthens confidence in the reliability of reported results.

Related Resources

• 7 Common ISO/IEC 17025 Nonconformities Found During Assessments
• What Happens When a Laboratory Fails Proficiency Testing?
• Why Compendial Methods Require Verification — Not Validation — in ISO/IEC 17025 Laboratories

About Lab Accreditation & Quality Partners

Lab Accreditation & Quality Partners (LabAQP) provides consulting services to help laboratories develop strong quality systems and successfully achieve ISO/IEC 17025 accreditation.