Difference Between IQC and EQA in Laboratory Quality Assessment

Laboratory quality assessment is essential for ensuring that diagnostic testing for patient samples in one or more analytes is accurate, consistent, and clinically reliable. Within this framework, Internal Quality Control (IQC) and External Quality Assessment (EQA) play complementary but distinct roles in monitoring performance and maintaining standards.

While IQC focuses on real-time control of testing processes within the laboratory, EQA provides an independent, external evaluation of performance across many laboratories. Understanding the difference between these two approaches is key to building a robust and effective laboratory quality assessment strategy.

In this article, we explore how IQC and EQA differ, how they work together, and why both are critical to high-quality laboratory practice.

What is Laboratory Quality Assessment?

Laboratory quality assessment refers to the structured processes used to monitor, evaluate, and improve the accuracy and reliability of laboratory testing. It encompasses both internal and external approaches to quality management, ensuring that results are consistent, reproducible, and fit for clinical decision-making.

Two of the most important components of laboratory quality assessment are Internal Quality Control (IQC) and External Quality Assessment (EQA). Together, they provide a comprehensive view of laboratory performance — both within the testing environment and in comparison with other laboratories.

What is EQA?

External Quality Assessment involves an independent, external service provider that assesses a laboratory's testing abilities. This involves the analysis of identical samples in many laboratories and the comparison of the results with other testing sites in relation to a target result. The main purpose of EQA is to benchmark the laboratory against other laboratories to ensure the consistency and reliability of test results. 

In an ideal world, a test result would be the same regardless of the testing location. EQA identifies where laboratories might need improvement, especially across disciplines such as Autoimmunity, Allergy & Immunodeficiency, Immunochemistry, and Oncology. It provides an objective evaluation, offering reassurance to both staff and service users by affirming that the testing conducted at their laboratory yields precise and dependable results.

A laboratory might undergo EQA for a variety of reasons, including to gain accreditation or certification, or because it is a mandatory legal requirement from local and national bodies. For a more detailed explanation of how EQA works in practice, see our guide to External Quality Assurance.

What Does a Good EQA Scheme Look Like?

A good EQA scheme should offer the following:

• Provide an assessment of performance of an assay (precision/bias) with respect to other test sites at a particular moment in time or cumulatively across time
• The range and number of samples should ensure assessment of the assay performance across the entire measuring range and clinically relevant decision points
• The frequency of sample cycles should be sufficient to detect any assay performance issues
• Consistent reporting and a quick turnaround time to ensure assay performance issues don’t go unnoticed 
• Comparing performance between laboratories and different assays and providing support and feedback to participating laboratories
• Involving a large number of participants to provide statistically robust data 
• Accreditation to ISO 17043 to enable confidence to users of the high standard of service provided

Key Responsibilities of EQA

Key responsibilities of EQA are to:

• Identify poorly performing assays or tests within laboratories in a timely manner
• Provide advice and guidance on how to improve
• Assist with harmonisation and standardisation, working towards minimising variation between patient results obtained at different test sites

What is IQC?

On the other hand, Internal Quality Control (IQC) is conducted by the laboratory itself. IQC monitors reproducibility and assesses whether the performance of an individual test is sufficiently similar to its previous performance. Most IQC procedures employ analysis of IQC materials and compare the results with predetermined limits of acceptability.

IQC focuses primarily on maintaining and improving the quality of testing processes and results within the testing site. Its goal is to ensure ongoing accuracy, precision, and reliability of test results within the laboratory. IQC aims to deal with issues in real time, in order to strive for continuous improvement and compliance with internal standards. 

IQC can also serve as a preparatory event for an external quality audit. It helps identify any non-conformances, allowing labs the opportunity to address them before the more critical EQA.

Key Responsibilities of IQC

The main responsibilities of IQC are to:

• Monitor assay performance on a regular basis
• Identification of any trends or shifts in IQC results that may impact patient test results 
• Assess reproducibility 
• Provide reassurance to the service provider that the testing systems are performing adequately

What Does a Good IQC Process Look Like?

For a successful IQC process, the laboratory should consider the following:

• How many IQCs are required
• How often do the IQCs need to be tested
• Where should the IQCs be located in the assay run
• What predetermined limits are in place to detect any unsatisfactory performance
• Use of independent IQC materials i.e different to the assay/test manufacturer
• How will any findings from the IQC process be shared with the management and staff 

How IQC and EQA Work Together in Laboratory Quality Assessment

IQC and EQA are not interchangeable — they serve different but complementary roles within a laboratory quality assessment framework.

EQA uses proficiency testing, which is where external providers send unknown samples to participating laboratories, and then perform tests and report their results back. The provider compares these results against expected values or results from multiple laboratories.

With IQC, laboratories conduct internal audits, where they evaluate the laboratory's procedures, equipment and performance against internal predetermined limits or standards. 

EQA provides an independent assessment of the performance of an assay (precision/bias) with respect to other test sites at a particular moment in time, or cumulatively across time. EQA is done periodically and retrospectively, while in comparison, IQC results are performed internally in real time and provide a measure of assay performance on a more frequent basis.

What are the Benefits of Quality Assurance?

IQC and EQA hold many benefits, including:

• Improving national and local standards
• Providing management with insights into their performance
• Revealing areas of difficulty
• Demonstrating a commitment to quality to customers
• Providing evidence of performance for accreditation bodies
• QA measures can decrease the need for retesting, reduce errors, and lower operational costs associated with repeat analyses

Strengthening Laboratory Quality Assessment Through IQC and EQA

Effective laboratory quality assessment depends on both internal monitoring and external validation. IQC ensures that testing remains stable and consistent day to day, while EQA provides independent assurance that results are comparable across laboratories and methods.

By integrating both approaches, laboratories can strengthen diagnostic accuracy, support accreditation requirements, and maintain confidence in their results.

To learn more about how external quality assessment supports laboratory performance, explore UK NEQAS IIA’s independent EQA programmes or read our guide to External Quality Assurance. We also offer a range of educational resources within our Digital Academy.