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Quality Control in the NHS Lab: EQA, IQA, and IQC Explained for Trainees

11 min read · Published: 2025-01-08 · Updated: 2026-03-12

Quality Control in the NHS Lab: EQA, IQA, and IQC Explained for Trainees

Quality control is one of the most important aspects of laboratory practice, yet it is also one of the areas that trainees often find confusing. Understanding the difference between IQC, IQA, and EQA — and how they work together to protect patients — is essential knowledge for any Biomedical Scientist. It is also a common topic in NHS interviews and IBMS portfolio assessments.

Why Quality Control Matters

Every result that leaves an NHS laboratory has the potential to influence clinical decisions. An incorrect potassium result could lead to unnecessary treatment. A falsely normal troponin could mean a patient with a myocardial infarction is sent home. Quality control exists to ensure that laboratory results are accurate, precise, and clinically reliable.

The three pillars of quality assurance in the laboratory — IQC, IQA, and EQA — work at different levels to provide a comprehensive safety net. Together, they form the quality management system that underpins ISO 15189:2022 accreditation, assessed by the United Kingdom Accreditation Service (UKAS).

Internal Quality Control (IQC)

What Is IQC?

Internal Quality Control is the day-to-day monitoring of analytical performance. It involves running control materials — samples with known target values — alongside patient specimens to check that the analyser is producing accurate and consistent results.

IQC materials are typically run at the start of each shift, after maintenance, after reagent changes, and at regular intervals throughout the day. Most laboratories use at least two levels of control (low and high) to check performance across the clinically relevant range.

Westgard Rules

The interpretation of IQC results is guided by Westgard rules, a set of decision criteria that help laboratory staff determine whether an analytical run is acceptable or whether action is needed. The most commonly applied rules include:

When a Westgard rule violation occurs, patient results from that run must not be reported until the issue is investigated and resolved.

What Happens When IQC Fails?

When IQC fails, the standard response follows a structured approach. First, rerun the control material to rule out a one-off error. If the failure persists, check for obvious causes: expired reagents, maintenance due, temperature issues, or sample problems. Escalate to a senior member of staff if the cause is not immediately apparent.

All IQC failures must be documented, including the action taken and the outcome. Patient results affected by the failure should be reviewed and, if necessary, repeated. This documentation is essential for UKAS inspections and demonstrates good laboratory governance.

Internal Quality Assurance (IQA)

What Is IQA?

Internal Quality Assurance is a broader process than IQC. While IQC focuses on analytical performance, IQA encompasses auditing and monitoring the entire laboratory process — from sample receipt through to result reporting. It is about ensuring that the laboratory's quality management system is working effectively.

IQA activities include:

Who Is Responsible?

While the quality manager or quality lead typically coordinates the IQA programme, every member of staff has a role. Trainees are expected to follow SOPs, participate in competency assessments, and report any deviations or non-conformances they observe. Understanding this shared responsibility is important for interview success.

External Quality Assessment (EQA)

What Is EQA?

External Quality Assessment involves an independent organisation sending samples to participating laboratories for analysis. The laboratory processes these samples using their routine methods and reports the results back. The EQA provider then compares results across all participating laboratories and issues a performance report.

EQA provides an objective, external check on laboratory performance that IQC alone cannot deliver. It identifies systematic biases, method-related differences, and performance outliers. Participation in EQA is a mandatory requirement for ISO 15189 accreditation.

UK EQA Providers

The principal EQA providers in the United Kingdom are:

What Happens When EQA Results Are Poor?

An unsatisfactory EQA result triggers a structured investigation. The laboratory must determine whether the poor result reflects a genuine analytical problem or a pre-analytical issue (such as sample handling). A root cause analysis is carried out, corrective actions are documented, and the outcome is monitored.

Persistent poor EQA performance is a serious concern. UKAS assessors review EQA reports during inspections, and repeated failures can lead to conditions being placed on a laboratory's accreditation. In extreme cases, accreditation for a specific test or discipline can be suspended.

How QC Links to UKAS and ISO 15189 Accreditation

ISO 15189:2022 is the international standard for medical laboratory quality and competence. In the UK, laboratories are assessed against this standard by UKAS. Accreditation is not legally mandatory, but it is a commissioning requirement — NHS England expects accredited laboratory services.

The standard requires laboratories to have a comprehensive quality management system that includes IQC, IQA, and participation in EQA. Specifically, laboratories must demonstrate:

Trainee Responsibilities

As a trainee Biomedical Scientist, your responsibilities in quality control include:

These are activities you should be recording in your IBMS registration portfolio as evidence of competence and professional practice.

Key Points

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