Introduction
A laboratory result is useful when there is reasonable confidence that it has been produced through an appropriate and controlled process.
This is why quality control, commonly abbreviated as QC, is an important part of laboratory practice.
Quality control involves planned operational techniques and activities used to monitor laboratory processes, identify problems and help control conditions that may affect the quality of results.
For beginners, it is important to understand that quality control is not simply about checking the final result.
It involves monitoring the processes that produce laboratory results.
QC can involve control materials, equipment monitoring, process checks, trend analysis, investigation of deviations and corrective action.
This article introduces the fundamentals of laboratory quality control and explains how QC connects with equipment, personnel, reagents, documentation and the wider laboratory quality-management system.
1. What Is Laboratory Quality Control?
Laboratory quality control is the set of operational techniques and activities used to monitor whether a laboratory process is performing within established requirements.
Depending on the laboratory discipline, QC may involve:
- Control materials
- Equipment checks
- Monitoring results
- Reviewing trends
- Establishing acceptance criteria
- Identifying deviations
- Investigating problems
- Taking corrective action
- Documenting findings
The exact QC process depends on the laboratory’s activities, methods and quality requirements.
2. Why Is Quality Control Important?
Quality control can help a laboratory:
- Detect errors
- Monitor analytical performance
- Identify trends
- Detect unexpected variation
- Support confidence in results
- Identify problems early
- Trigger investigation when requirements are not met
- Support corrective action
QC therefore provides an important mechanism for monitoring laboratory processes.
It is not a substitute for a complete quality-management system.
3. Quality Control Is More Than Testing Control Samples
In some laboratory environments, QC includes the use of control materials.
However, laboratory quality also depends on many other activities.
These may include:
- Equipment maintenance
- Calibration
- Staff competence
- Sample handling
- Reagent management
- Standard Operating Procedures
- Environmental control
- Documentation
- Method control
- Data management
Quality cannot be created by one QC activity alone.
A control result may be acceptable while another part of the laboratory process has a problem.
This is why QC should be viewed as part of an interconnected quality system.
4. The Three Stages of Laboratory Work
Laboratory activities are often considered across three broad stages:
Pre-Analytical Stage
This includes activities before the actual analysis.
Examples may include:
- Sample collection
- Patient or sample identification
- Transportation
- Storage
- Sample preparation
- Acceptance or rejection of samples
Problems at this stage can affect the quality of subsequent results.
Analytical Stage
This includes activities involved in performing the test or measurement.
Examples include:
- Instrument operation
- Reagent use
- Testing procedures
- Measurement
- Quality-control checks
- Equipment monitoring
Post-Analytical Stage
This includes activities after analysis.
Examples may include:
- Result review
- Result validation where applicable
- Reporting
- Data management
- Record keeping
- Communication of results
Quality considerations can therefore apply throughout the laboratory process, not only during analysis.
5. What Are Control Materials?
Control materials are materials with defined or expected characteristics that can be used to monitor a laboratory process.
They are used according to the laboratory’s established method and QC procedure.
Control materials are not necessarily the same as routine test samples.
Depending on the laboratory discipline, control materials may be used to monitor aspects of analytical performance such as:
- Accuracy-related performance
- Precision
- Stability
- Consistency
- Changes in analytical performance
The specific control materials and acceptance criteria depend on the laboratory method.
6. Understanding QC Acceptance Criteria
A laboratory should establish appropriate criteria for determining whether QC results are acceptable.
Acceptance criteria provide a basis for deciding whether a process is operating as expected.
When a QC result falls outside an established requirement, the laboratory should follow its procedure for investigation and corrective action.
An unexpected QC result should not simply be ignored because a routine sample result appears reasonable.
The purpose of QC is to identify potential problems before they compromise laboratory work.
7. QC Charts and Trend Monitoring
Some laboratories use graphical methods to monitor QC results over time.
Charts can help laboratory personnel identify patterns such as:
- Sudden shifts
- Gradual trends
- Increased variability
- Unusual patterns
- Changes in process performance
Trend monitoring can provide an early indication that something in the laboratory process may require investigation.
The specific charting method and interpretation should follow the laboratory’s established QC procedure.
8. Sources of Quality-Control Problems
QC problems can result from many different sources.
Equipment
Examples include:
- Calibration issues
- Maintenance problems
- Instrument malfunction
- Incorrect equipment settings
- Environmental effects on equipment
Reagents and Materials
Possible issues include:
- Expired materials
- Incorrect storage
- Preparation errors
- Contamination
- Deterioration
- Incorrect material selection
Personnel
Examples include:
- Incorrect technique
- Inadequate training
- Procedural errors
- Failure to follow an SOP
- Misinterpretation of instructions
Environment
Factors may include:
- Temperature
- Humidity
- Power conditions
- Vibration
- Contamination
- Other conditions relevant to the method
A failed QC result should therefore not automatically be attributed to one cause.
9. What Should Happen When QC Fails?
The laboratory should follow its established procedure.
A general process may include:
- Identify the failed control.
- Determine the affected process or work.
- Stop or control affected work where required.
- Check obvious causes.
- Review equipment status.
- Check reagents and materials.
- Review recent maintenance or calibration.
- Review relevant procedures and records.
- Investigate the problem.
- Take appropriate corrective action.
- Repeat appropriate QC checks.
- Document the investigation and outcome.
The exact response depends on the laboratory method, quality system and significance of the deviation.
10. Quality Control and Equipment
Equipment management is closely connected to QC.
Suppose a temperature-controlled instrument begins producing unusual QC results.
The laboratory may need to consider:
- Equipment condition
- Temperature records
- Maintenance history
- Calibration status
- Equipment settings
- Environmental conditions
- Recent repairs or adjustments
This demonstrates why laboratory quality is interconnected.
An equipment problem can become a QC problem, while a QC trend may also provide evidence that equipment performance requires investigation.
11. Quality Control and Reagent Management
Reagents and other laboratory materials can have a significant effect on QC performance.
Laboratories should follow appropriate procedures for:
- Receiving materials
- Identification
- Storage
- Preparation
- Labelling
- Expiry control
- Contamination prevention
- Disposal
When QC results change unexpectedly, reagent-related causes may need to be considered alongside equipment and procedural factors.
12. Quality Control and Personnel Competence
People are an important part of laboratory quality.
QC problems may sometimes be associated with:
- Inadequate training
- Incorrect technique
- Failure to follow procedures
- Misunderstanding of equipment operation
- Poor documentation
Training and competency assessment can therefore support effective quality control.
Laboratory personnel should understand not only how to perform a procedure but also why QC checks are required.
13. Quality Control and Documentation
QC activities should be documented according to the laboratory’s record-control procedures.
QC records may include:
- Date
- Test or process
- Control identification
- QC result
- Acceptance criteria
- Operator
- Equipment identification where applicable
- Investigation findings
- Corrective action
- Final outcome
Good documentation allows the laboratory to demonstrate what was checked, what was found and what action was taken.
14. Quality Control and Corrective Action
QC is most useful when unexpected results lead to appropriate action.
Corrective action may involve:
- Correcting an equipment problem
- Replacing unsuitable reagents
- Repeating an approved procedure
- Providing additional training
- Reviewing an SOP
- Investigating environmental conditions
- Performing maintenance
- Reviewing calibration status
The action should address the identified problem rather than simply making the QC result appear acceptable.
15. Quality Control vs Quality Assurance
Quality control and quality assurance are related but different concepts.
Quality Control
QC focuses on operational techniques and activities used to monitor and control processes.
Quality Assurance
Quality assurance is broader and involves planned and systematic activities intended to provide confidence that quality requirements will be fulfilled.
QC is therefore one component of a broader quality-management system.
A laboratory needs both effective operational controls and a wider system for managing quality.
16. Quality Control vs Quality Management
Quality management encompasses the broader system through which a laboratory plans, controls, assures and improves the quality of its activities.
This may include:
- Quality policy
- Procedures
- Staff competence
- Equipment management
- QC
- QA
- Internal audits
- Corrective action
- Document control
- Risk management
- Continuous improvement
QC therefore operates within a much larger framework.
17. Common Quality-Control Mistakes
Laboratories should avoid practices such as:
Ignoring Failed Controls
A failed QC result should be investigated according to procedure.
Changing Results to Make Them Appear Acceptable
QC records should accurately reflect what occurred.
Failing to Document Investigations
An undocumented investigation creates a gap in the quality record.
Using Expired or Improperly Stored Control Materials
Control materials should be managed according to their applicable requirements.
Ignoring Equipment Problems
Equipment problems can affect QC performance and may require investigation.
Repeating Tests Indefinitely Without Investigating
Repeatedly obtaining an unexpected QC result without addressing its possible cause does not solve the underlying problem.
Treating QC as Only the QC Officer’s Responsibility
Quality control depends on the activities of laboratory personnel throughout the workflow.
18. Practical Example: Failed QC Result
Imagine that an analytical instrument produces a QC result outside its established acceptance range.
A responsible response is not simply to continue reporting routine results.
The laboratory may need to:
- Confirm the QC result.
- Check the applicable acceptance criteria.
- Determine which work may be affected.
- Review equipment status.
- Check reagents and control materials.
- Review recent maintenance or calibration.
- Review the operating procedure.
- Investigate the likely cause.
- Take corrective action.
- Repeat appropriate QC checks.
- Document the investigation.
Only after the applicable requirements have been satisfied should affected work proceed according to the laboratory’s established procedure.
19. Developing Good Quality-Control Practices
Laboratory professionals can support effective QC by:
- Understanding applicable QC procedures
- Following SOPs
- Using appropriate control materials
- Checking equipment status
- Recording QC results accurately
- Monitoring trends
- Reporting unexpected results
- Investigating deviations
- Documenting corrective actions
- Participating in competency development
- Reviewing procedures when recurring problems occur
Effective QC is a continuous process rather than a one-time activity.
20. Quality Control and Continuous Improvement
QC records can provide useful information beyond individual test runs.
When reviewed over time, QC data may help laboratories identify:
- Recurring problems
- Equipment-related trends
- Reagent issues
- Training needs
- Process variation
- Opportunities for improvement
This makes QC an important source of information for continuous quality improvement.
The objective is not simply to collect QC records.
The objective is to use information from those records to help control and improve laboratory processes.
21. FAQs
What is laboratory quality control?
Laboratory quality control is the set of operational techniques and activities used to monitor and control laboratory processes against established requirements.
Why is QC important in a laboratory?
QC helps identify problems, monitor process performance, detect variation and trigger investigation when established requirements are not met.
Is QC the same as quality assurance?
No. QC focuses on operational monitoring and control, while quality assurance is broader and provides confidence that quality requirements will be fulfilled.
What are control materials?
Control materials are materials with defined or expected characteristics used to monitor a laboratory process according to an established QC procedure.
What should a laboratory do when QC fails?
The laboratory should follow its established procedure. This may involve controlling affected work, investigating the cause, checking equipment and materials, taking corrective action, repeating appropriate QC checks and documenting the outcome.
Can equipment problems cause QC failure?
Yes. Equipment condition, calibration, maintenance, settings and environmental factors can contribute to QC problems.
Can QC detect problems before routine results are affected?
QC is designed to monitor laboratory processes and can help identify problems or changes in performance that may require investigation.
Why should QC results be documented?
Documentation provides evidence of QC activities and allows laboratories to review results, investigate deviations and identify trends.
Is quality control only the responsibility of one person?
No. Effective quality control depends on appropriate practices throughout the laboratory workflow.
How can laboratory professionals improve their QC skills?
They can study applicable QC procedures, understand acceptance criteria, develop equipment and measurement skills, learn to recognize trends and participate in relevant laboratory training.
Conclusion
Quality control helps laboratories monitor their processes and detect problems that may affect laboratory work and results.
Effective QC involves more than producing control records.
It requires appropriate procedures, defined acceptance criteria, competent personnel, suitable equipment, controlled materials, accurate documentation, investigation of deviations and appropriate corrective action.
QC works best when integrated with equipment management, calibration, maintenance, personnel competence, SOPs and the wider laboratory quality-management system.
Knowledge Tech Hub Practical Takeaway
Think of QC as an early-warning system:
Measure → Compare → Detect → Investigate → Correct → Document
The purpose is not simply to produce QC records.
The purpose is to use those records to control laboratory processes, identify problems and support continuous improvement.
Suggested Internal Links
- Laboratory Equipment Calibration: What Every Laboratory Professional Should Know
- Calibration vs Maintenance: Understanding the Difference
- Laboratory Equipment Maintenance: A Complete Practical Guide
- Preventive Maintenance for Laboratory Equipment
- Laboratory Equipment Troubleshooting: A Practical Guide
- Laboratory Quality Assurance: Principles, Processes and Best Practices
- Laboratory Documentation and Record Keeping
- Laboratory Standard Operating Procedures (SOPs): A Practical Guide
- Common Laboratory Errors and How to Prevent Them
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References and Further Reading
- World Health Organization — Laboratory Quality Management System resources
- International Organization for Standardization — ISO 15189, where applicable to medical laboratories
- International Organization for Standardization — ISO/IEC 17025, where applicable to testing and calibration laboratories
- Applicable national laboratory quality requirements
- Laboratory quality-control SOPs and procedures
- Manufacturer equipment and QC documentation