Quality control vs quality assurance is the difference between checking whether day-to-day testing is performing as expected and managing the wider system that makes laboratory results reliable. Quality control (QC) includes activities such as running control materials, reviewing shifts and trends and deciding whether an analytical run is acceptable. Quality assurance (QA) is broader: it includes policies, staff competence, document control, audits, risk management, external assessment, accreditation and continual improvement across the whole testing pathway.
What Is Quality Control?
Quality control is the practical, routine monitoring used to detect problems in the analytical process.
In a clinical laboratory, an analyser can produce a number even when something has gone wrong. Reagent deterioration, calibration drift, pipetting issues, temperature problems and instrument faults can all affect results.
QC is designed to identify this type of problem before patient results are released.
Typical QC activities include:
- analysing control material with known expected behaviour
- plotting control results over time
- reviewing whether results fall within established limits
- looking for shifts, trends or sudden errors
- checking calibration and reagent performance
- taking corrective action when control performance is unacceptable
- documenting what happened and how it was resolved
QC is therefore closely connected to the question: Can the laboratory trust today’s analytical process?
Internal Quality Control
Internal quality control (IQC) is performed within the laboratory, often every day or at defined intervals depending on the test and analyser.
A control material is analysed in a similar way to a patient sample. Because the laboratory has an established target and acceptable variation for the control, unexpected movement can signal a problem.
For a quantitative test, staff may monitor control results across different concentration levels. An analyser measuring glucose, for example, might use more than one control level to check performance across clinically important parts of the measuring range.
The exact frequency and rules depend on the assay, risk, manufacturer instructions and laboratory procedure.
IQC is not about “making the control pass”. If the control is outside acceptable limits, staff investigate why before deciding whether patient results can be safely released.
Levey-Jennings Charts
A Levey-Jennings chart is a common way to visualise QC performance.
The chart plots control values against time around a target mean and standard-deviation limits. Looking at individual points and patterns can help laboratory staff identify:
- random error
- a gradual trend
- a sustained shift
- sudden loss of analytical stability
Laboratories may use formal decision rules alongside these charts.
The value of the chart is not the graphic itself. It is the ability to detect changes in analytical behaviour early enough to prevent unreliable patient results from being reported.
What Is Quality Assurance?
Quality assurance is broader than QC.
QA asks whether the entire laboratory service is designed, managed and monitored so that results are fit for their intended clinical purpose.
This includes the pre-analytical, analytical and post-analytical phases.
Examples include:
- sample identification and acceptance criteria
- staff training and competency assessment
- standard operating procedures
- equipment maintenance
- reagent and stock control
- internal quality control
- external quality assessment
- result authorisation
- critical-result communication
- incident management
- audit
- risk management
- document control
- corrective and preventive actions
- continual improvement
UKAS explains that ISO 15189 accreditation assesses both a medical laboratory’s quality-management system and its competence to perform specified activities.
QC vs QA: The Core Difference
| Area | Quality Control | Quality Assurance |
|---|---|---|
| Scope | Narrower, test/process focused | Whole quality-management system |
| Main question | Is this analytical process performing correctly now? | Is the service designed and operating reliably overall? |
| Typical activities | Control samples, charts, rule review, run acceptance | SOPs, training, audits, EQA, risk, accreditation |
| Time scale | Often daily or per analytical run | Continuous and system-wide |
| Problem type | Detects analytical instability or error | Prevents, identifies and manages system failures |
| Relationship | One component of QA | Includes QC plus wider processes |
QC and QA are therefore not competing systems. QC sits inside the broader QA framework.
External Quality Assessment
External quality assessment (EQA) gives a laboratory an independent comparison of its performance.
An EQA provider distributes samples to participating laboratories. The laboratories test them, submit results and receive feedback comparing performance with an assigned target or peer group.
EQA can reveal issues that local IQC may not detect easily, including systematic bias between methods or laboratories.
The IBMS has emphasised the importance of national quality-assurance structures and EQA for patient safety and public confidence in pathology.
EQA does not replace IQC. A laboratory needs both:
- IQC for frequent monitoring of day-to-day analytical stability
- EQA for independent, periodic assessment against an external standard or peer performance
Standard Operating Procedures
A standard operating procedure, or SOP, describes how a process should be performed.
A strong quality system controls SOPs so that:
- the current authorised version is available
- obsolete versions are removed from routine use
- responsibilities are clear
- changes are reviewed and approved
- staff are trained where required
- records show what version was in force at a given time
Document control sounds administrative, but it directly affects analytical consistency. If different staff follow different versions of a procedure, variation and risk increase.
Audits
Laboratory audits check whether documented processes are actually being followed and whether the system is effective.
An audit may examine:
- sample reception
- equipment records
- quality-control review
- reporting
- competency records
- incident management
- traceability
- compliance with a standard or local procedure
An audit is not simply about finding fault. A useful audit identifies gaps and creates evidence for improvement.
ISO 15189 and UKAS Accreditation
In the UK, medical laboratories commonly work within the framework of ISO 15189, the international standard covering quality and competence in medical laboratories.
UKAS is the national accreditation body that assesses laboratories against ISO 15189 requirements.
Accreditation provides independent assurance that a laboratory has a functioning quality-management system and can demonstrate competence for the activities within its accredited scope.
This is broader than passing a QC sample. A laboratory could have acceptable daily QC yet still have weaknesses in training, sample identification, document control or result communication. QA and accreditation address these wider risks.
Why QC and QA Matter for Patient Safety
Laboratory results influence clinical decisions. A small analytical or identification error can therefore have consequences beyond the laboratory bench.
Consider several examples:
- A potassium analyser drifts upward but QC does not detect it.
- A patient sample is labelled incorrectly before analysis.
- A critical result is generated correctly but not communicated.
- A new reagent lot produces bias that is not recognised.
- A staff member uses an obsolete procedure.
Only the first example is primarily an analytical QC problem. The others show why QA must cover the entire pathway.
Quality management aims to reduce the probability that an error reaches the patient.
What Biomedical Science Students Should Understand
For students, one of the most useful distinctions is:
QC checks the performance of the test. QA checks the performance of the system.
In practice, biomedical scientists participate in both.
A biomedical scientist may:
- review daily IQC
- investigate a control failure
- document corrective action
- participate in EQA
- update an SOP
- perform or support an audit
- assess a new reagent lot
- help validate or verify a method
- record incidents
- contribute to training and competency assessment
These activities are part of professional laboratory practice, not optional extras around the “real” testing work.
For wider context, see what is biomedical science and biomedical science careers.
Common Misunderstandings
“QC and QA mean the same thing”
They are related, but QA is broader.
“If QC passes, every patient result must be correct”
Passing QC increases confidence in analytical performance but cannot detect every pre-analytical, clerical or clinical-context problem.
“EQA replaces internal controls”
It does not. EQA is periodic and external; IQC is local and frequent.
“Accreditation guarantees zero errors”
No quality system can promise zero errors. Accreditation provides structured assurance of quality and competence and requires systems for identifying and managing problems.
Key Points
- QC is the routine monitoring of analytical performance.
- QA covers the entire laboratory quality system.
- IQC uses control material to detect analytical instability.
- Levey-Jennings charts help visualise control performance over time.
- EQA provides independent comparison with external targets or peers.
- SOPs, audits, competence, risk management and document control are QA activities.
- ISO 15189 and UKAS accreditation provide a wider framework for medical-laboratory quality and competence.
- Both QC and QA support patient safety.
References
- Institute of Biomedical Science. Joint statement on quality assurance issued. https://www.ibms.org/resource/joint-statement-on-quality-assurance-issued.html
- Institute of Biomedical Science. Guidance on the roles of Quality Personnel. https://www.ibms.org/resources/documents/quality-management-in-laboratories/2guidance-on-the-roles-of-quality-personnel-in-clinical-laboratories.pdf
- UKAS. Medical Laboratory Accreditation – ISO 15189. https://www.ukas.com/accreditation/standards/medical-laboratory-accreditation/
- UKAS. Quality Assurance and Control in Medical Laboratories. https://www.ukas.com/training-and-advisory/training/courses/quality-assurance-medabs/
This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional about your results.
Biomedical Science Careers: Roles, Specialisms, and How to Qualify in the UK
Frequently Asked Questions
What is the main difference between quality control and quality assurance?
Quality control focuses mainly on whether analytical testing is performing correctly, while quality assurance covers the wider system including staff competence, SOPs, audits, EQA, incidents, risk management and accreditation.
Is internal quality control part of quality assurance?
Yes. Internal quality control is one component of the broader quality-assurance and quality-management system used in a medical laboratory.
What is a Levey-Jennings chart used for?
It plots quality-control results over time around an expected target and limits, helping laboratory staff detect changes such as trends, shifts or unexpected analytical variation.
What is EQA in a medical laboratory?
External quality assessment is an independent programme in which laboratories analyse distributed samples and compare their performance with assigned values or peer groups. It complements rather than replaces internal QC.
What is ISO 15189?
ISO 15189 is an international standard specifying requirements for quality and competence in medical laboratories. In the UK, UKAS assesses medical laboratories for accreditation against the standard.
Why do biomedical scientists need to understand QC and QA?
Biomedical scientists are responsible for producing and supporting reliable laboratory results. Their work can include reviewing controls, investigating failures, following SOPs, participating in EQA, auditing processes and documenting corrective action.