Introduction
A laboratory depends on consistent and controlled procedures.
Different people may perform the same task at different times, but the expected process and quality requirements should remain consistent.
This is one of the main purposes of Standard Operating Procedures (SOPs).
A laboratory SOP provides documented instructions for performing a defined activity. It can cover equipment operation, sample handling, testing procedures, cleaning, maintenance, quality control, safety activities, documentation and other laboratory processes.
Good SOPs are not simply documents kept in a file or folder.
They are working tools that help laboratory personnel understand:
- What to do
- How to do it
- What to record
- What precautions to take
- What to do when something goes wrong
For an SOP to be useful, it must be appropriate for the activity, controlled, understood by users and kept current.
1. What Is a Laboratory SOP?
A Standard Operating Procedure (SOP) is a controlled document that describes how a defined laboratory activity should be performed.
Examples include SOPs for:
- Operating a centrifuge
- Using a microscope
- Operating an analyser
- Receiving laboratory samples
- Handling and storing reagents
- Cleaning laboratory equipment
- Performing a particular test
- Performing quality-control activities
- Managing nonconforming work
- Handling laboratory waste
- Responding to equipment failure
- Recording laboratory results
The exact content of an SOP depends on the activity and the laboratory’s quality requirements.
2. Why Are Laboratory SOPs Important?
SOPs contribute to laboratory quality in several ways.
They promote consistency
An SOP gives personnel a common procedure to follow.
This can reduce unnecessary variation between operators.
They support training
New personnel can use approved SOPs as part of their training and familiarization.
They support quality management
Documented procedures help demonstrate that important activities are defined and controlled.
They improve traceability
SOPs can identify what information should be recorded and what records should be retained.
They support safety
Procedures can identify hazards, precautions and responses to abnormal situations.
They preserve institutional knowledge
Experienced personnel may have developed important practical knowledge over time. Appropriate documentation helps preserve that knowledge within the laboratory.
3. What Should a Laboratory SOP Contain?
A useful SOP should contain enough information for a trained and authorized person to perform the activity correctly.
A typical SOP may contain:
| SOP Section | Purpose |
| Title | Identifies the procedure |
| SOP number/ID | Provides document identification |
| Version/revision number | Identifies the current version |
| Effective date | Shows when the procedure became active |
| Review date | Indicates when review is due, where applicable |
| Purpose | Explains why the procedure exists |
| Scope | Defines where and when it applies |
| Responsibilities | Identifies relevant roles |
| Definitions | Explains important terms |
| Safety precautions | Identifies hazards and controls |
| Materials/equipment | Lists required resources |
| Procedure | Provides instructions |
| Quality control | Describes applicable checks |
| Records | Identifies information that must be documented |
| References | Lists supporting sources |
| Revision history | Shows important changes |
| Approval | Identifies authorized approval |
Not every laboratory will use exactly the same format.
The SOP structure should follow the laboratory’s quality-management and document-control system.
4. SOP vs Policy vs Work Instruction
These terms are sometimes confused.
Policy
A policy generally states an organization’s direction, principle or requirement.
SOP
An SOP explains how a defined activity should be performed.
Work Instruction
A work instruction may provide detailed instructions for a particular task within a broader procedure.
For example:
Policy:
Laboratory equipment must be appropriately maintained.
SOP:
Procedure for Preventive Maintenance of Laboratory Centrifuges.
Work Instruction:
Detailed cleaning procedure for a specific centrifuge model.
Terminology can vary between organizations, so laboratories should follow their established document-control system.
5. How to Write a Good Laboratory SOP
Developing a useful SOP requires more than putting technical information into a document.
Step 1: Define the activity
Be specific about what the SOP covers.
Instead of:
Laboratory Equipment Procedure
use something more specific such as:
Procedure for Routine Operation of a Benchtop Centrifuge
Step 2: Identify the users
Consider who will perform the activity and what level of training or authorization is required.
Step 3: Define the scope
Make clear what the procedure covers and, where necessary, what it does not cover.
Step 4: Describe the process logically
The procedure should generally follow the actual workflow.
Step 5: Use clear language
Avoid unnecessary jargon and ambiguous instructions.
Instead of:
Operate the instrument appropriately.
provide specific instructions relevant to the equipment and procedure.
Step 6: Identify critical points
Highlight steps where an error could affect:
- Safety
- Equipment performance
- Sample integrity
- Measurement quality
- Results
Step 7: Identify required records
State what information must be documented.
Examples include:
- Equipment log
- Maintenance record
- QC record
- Sample record
- Test worksheet
- Incident report
6. SOPs Should Reflect Actual Laboratory Practice
An SOP should describe a process that the laboratory can actually perform.
A common problem occurs when an SOP is written without considering:
- Available equipment
- Personnel competence
- Laboratory facilities
- Actual workflow
- Applicable requirements
- Manufacturer instructions
- Required records
This can result in a procedure that looks complete on paper but is difficult or impossible to implement.
SOP development should therefore involve people who understand the activity and, where appropriate, those who will actually perform it.
7. Manufacturer Instructions and Laboratory SOPs
For equipment-related procedures, manufacturer documentation can be an important source of technical information.
Laboratory SOPs should take applicable manufacturer instructions into account.
However, a laboratory should not simply copy a manufacturer’s manual and call it an SOP.
The laboratory SOP should address the laboratory’s own:
- Workflow
- Responsibilities
- Safety requirements
- Records
- Quality controls
- Equipment identification
- Authorization requirements
The procedure should also remain consistent with applicable requirements.
8. Document Control Is Essential
An SOP should be controlled so personnel can identify which version is currently approved.
Important controls can include:
- SOP identification number
- Version or revision number
- Effective date
- Approval status
- Controlled distribution
- Revision history
- Review process
- Withdrawal of obsolete versions
Using an outdated SOP can create inconsistencies and quality problems.
A laboratory should therefore have a clear process for replacing or withdrawing obsolete documents.
9. SOP Approval
Before an SOP becomes an approved working procedure, it should normally pass through the laboratory’s established review and approval process.
Depending on the organization, this may involve:
- Drafting
- Technical review
- Quality review where applicable
- Approval by an authorized person
- Document registration
- Controlled distribution
- Implementation
The person who writes an SOP is not necessarily the person authorized to approve it.
Responsibilities should be clearly defined by the laboratory’s quality system.
10. Training and Competency
Simply publishing an SOP does not guarantee that personnel can perform the procedure correctly.
Training may involve:
- Introduction to the procedure
- Review of the SOP
- Demonstration
- Supervised practice
- Competency assessment where applicable
- Authorization to perform the activity independently
Training and competency records should be maintained according to the laboratory’s quality system.
Competence is particularly important for activities involving:
- Complex equipment
- Safety risks
- Critical measurements
- Specialized testing
- Quality-sensitive processes
11. SOPs and Authorization
Not every person who can read an SOP should automatically be authorized to perform the associated activity.
The laboratory may establish authorization requirements based on:
- Training
- Competence
- Experience
- Risk
- Job responsibilities
This helps ensure that procedures are performed by appropriately qualified personnel.
12. Reviewing and Updating SOPs
Laboratory procedures should not remain unchanged indefinitely.
An SOP may need review when:
- Equipment is replaced
- A test method changes
- Manufacturer instructions change
- A safety issue is identified
- A quality problem occurs
- Applicable requirements change
- Laboratory workflow changes
- New technology is introduced
- A review identifies outdated information
The purpose of review is to determine whether the procedure remains suitable and appropriate.
A review does not necessarily mean that the SOP must change. Sometimes review may confirm that the existing procedure remains appropriate.
13. What Happens When a Procedure Changes?
A controlled change process can help prevent confusion.
A typical process may be:
Identify change → Assess impact → Revise SOP → Review → Approve → Train affected personnel → Implement → Monitor
For example, if a laboratory replaces a centrifuge with a different model, the laboratory may need to review:
- Operating steps
- Safety requirements
- Rotor information
- Maintenance requirements
- Records
- Training needs
- Related SOPs
The exact change-control process depends on the laboratory’s quality-management system.
14. Revision History
A revision history helps users understand what has changed between versions.
It may include:
| Version | Date | Description of Change | Approved By |
| 1.0 | Date | Initial issue | Authorized person |
| 1.1 | Date | Minor procedural update | Authorized person |
| 2.0 | Date | Major revision following equipment change | Authorized person |
The exact format will depend on the laboratory’s document-control procedure.
15. SOPs and Records
An SOP should make clear what records need to be generated when the procedure is performed.
For example, an equipment SOP may require:
- Equipment-use log
- Cleaning record
- Maintenance record
- QC record
- Fault report
A testing SOP may require:
- Sample record
- Test worksheet
- QC record
- Result record
This connection between procedure and record strengthens traceability.
16. SOPs and Quality Control
Where quality-control activities are required, the SOP should describe the relevant process.
Depending on the activity, this may include:
- QC materials
- Acceptance criteria
- Frequency
- Required records
- Actions when QC fails
The SOP should make clear what personnel are expected to do when established requirements are not met.
17. SOPs and Laboratory Safety
Safety considerations should be included where relevant.
An SOP may identify:
- Hazards
- Required PPE
- Safe operating conditions
- Emergency procedures
- Waste-disposal requirements
- Actions to take following equipment malfunction or exposure
Safety information should be appropriate to the specific activity rather than added simply as generic text.
18. Common Laboratory SOP Mistakes
1. SOPs are too vague
Personnel may still have to guess what to do.
2. SOPs are unnecessarily complicated
Excessive detail can make procedures difficult to use.
3. Old versions remain available
Personnel may accidentally use outdated instructions.
4. SOPs are not reviewed
Procedures can become inconsistent with current equipment or practices.
5. Personnel are not trained
A document cannot replace appropriate practical training.
6. Procedures do not identify required records
Important evidence of completed work may be lost.
7. Manufacturer instructions are ignored
Equipment-specific procedures should take applicable manufacturer instructions into account.
8. SOPs do not address abnormal situations
Personnel may know what to do during normal operation but not what to do when something goes wrong.
9. SOPs describe activities that are not actually performed
This can create a gap between documented procedures and laboratory practice.
19. Practical Example: Centrifuge Operation SOP
Consider a laboratory that regularly uses a centrifuge.
A suitable SOP might address the following.
Before operation
- Inspect the equipment.
- Confirm that the appropriate rotor is installed.
- Check the condition of tubes and accessories.
- Confirm required settings.
- Verify that the equipment is available for use according to its status.
During operation
- Balance samples appropriately.
- Secure the rotor or accessories.
- Select the required operating parameters.
- Start the equipment according to the approved procedure.
- Monitor for abnormal conditions.
After operation
- Allow the centrifuge to stop completely.
- Remove samples safely.
- Inspect the relevant areas.
- Clean the equipment according to the procedure.
- Record required information.
If a problem occurs
The SOP should identify the appropriate response, such as:
- Stop the activity when safe to do so.
- Follow applicable safety procedures.
- Do not continue using unsafe equipment.
- Report the fault.
- Document the event where required.
- Follow the laboratory’s equipment-fault procedure.
The actual procedure must be based on the specific centrifuge, manufacturer instructions, laboratory requirements and intended application.
20. SOPs and Laboratory Quality Assurance
SOPs are an important part of a broader laboratory quality system.
They can support:
- Quality control
- Quality assurance
- Training
- Equipment management
- Documentation
- Risk management
- Internal audits
- Corrective action
- Continuous improvement
However, having SOPs does not by itself demonstrate that a laboratory has an effective quality system.
The procedures must be implemented, understood, monitored and reviewed.
21. SOPs and Internal Audits
Internal audits can examine whether personnel are following approved procedures.
An audit may compare:
What the SOP says should happen
with
What actually happens in the laboratory.
If differences are identified, the laboratory may need to determine whether:
- Personnel need additional training
- The SOP is unclear
- The SOP is outdated
- The actual process needs correction
- A nonconformity needs to be managed
This makes audits useful for identifying gaps between documented procedures and actual practice.
22. SOPs and Continuous Improvement
SOPs should evolve when laboratory processes change or when experience identifies opportunities for improvement.
Useful sources of information may include:
- Audit findings
- Equipment problems
- QC results
- Incidents
- Nonconformities
- Staff feedback
- Changes in equipment
- Changes in methods
- Applicable requirement changes
An SOP revision should be controlled rather than made informally.
23. A Practical SOP Development Workflow
A laboratory can use a structured process such as:
Identify → Draft → Review → Approve → Train → Implement → Monitor → Review
Identify
Determine whether an SOP is needed and define its scope.
Draft
Develop the procedure using appropriate technical information.
Review
Have appropriate personnel review the content.
Approve
Obtain authorization according to the laboratory’s document-control system.
Train
Ensure affected personnel understand the revised or new procedure.
Implement
Place the approved SOP into controlled use.
Monitor
Observe implementation and identify problems.
Review
Review the SOP periodically and whenever significant changes occur.
24. How to Make Laboratory SOPs More Practical
A useful SOP should be easy for an appropriately trained user to follow.
Consider:
- Using clear headings
- Numbering steps
- Keeping instructions in logical order
- Defining technical terms where necessary
- Separating normal operation from abnormal situations
- Highlighting critical safety points
- Identifying required records
- Using tables or checklists where appropriate
- Avoiding unnecessary repetition
- Linking the procedure to related documents
The objective is not to make an SOP as long as possible.
The objective is to make it sufficiently clear and complete for its intended purpose.
25. Frequently Asked Questions
What does SOP mean in a laboratory?
SOP means Standard Operating Procedure. It is a controlled document that describes how a defined laboratory activity should be performed.
Who should write a laboratory SOP?
An SOP should normally be prepared or reviewed by personnel with appropriate knowledge and competence in the activity. It should then be approved according to the laboratory’s document-control process.
How often should laboratory SOPs be reviewed?
The review interval depends on the laboratory’s quality system and applicable requirements. SOPs should also be reviewed when significant changes occur.
Can one SOP cover several pieces of equipment?
Sometimes. However, the scope must remain clear, and significantly different equipment may require separate procedures or equipment-specific work instructions.
Are laboratory SOPs required for quality management?
Documented procedures are an important component of many laboratory quality-management systems. Exact requirements depend on the laboratory’s activities and applicable standards or regulations.
Can an SOP replace practical training?
No. An SOP provides documented instructions, but personnel may still require training, supervised practice and competency assessment appropriate to the activity.
Should an SOP include manufacturer instructions?
Relevant manufacturer instructions should be considered when developing equipment procedures. The laboratory SOP should translate applicable information into the laboratory’s own controlled workflow and responsibilities.
What should happen when an SOP becomes outdated?
It should be reviewed and revised where necessary. The obsolete version should be withdrawn or otherwise controlled according to the laboratory’s document-control procedure.
What makes an SOP effective?
An effective SOP should be clear, appropriate to the activity, technically sound, controlled, accessible to authorized users, supported by training and kept current.
Conclusion
Laboratory SOPs provide a structured way to document how important activities should be performed.
A good SOP should be:
- Clear
- Controlled
- Practical
- Current
- Technically appropriate
- Supported by appropriate training
When properly implemented, SOPs help laboratories improve consistency, support staff training, strengthen documentation, improve traceability and contribute to reliable laboratory operations.
An SOP is therefore not simply a document.
It is a practical tool within the laboratory quality system.
Knowledge Tech Hub Practical Takeaway
An SOP should help answer four basic questions:
What should be done?
How should it be done?
What should be recorded?
What should happen if something goes wrong?
A useful additional question is:
How will we know that the procedure remains current and effective?
If an SOP cannot answer these questions appropriately for its intended activity, it may need review or improvement.
Suggested Internal Links
- Laboratory Safety: Essential Rules Every Laboratory Professional Should Know
- Laboratory Equipment: Names, Functions and Uses
- How to Use Laboratory Equipment Correctly: A Beginner’s Guide
- Laboratory Equipment Maintenance: A Complete Practical Guide
- Preventive Maintenance for Laboratory Equipment
- Laboratory Equipment Troubleshooting: A Practical Guide
- Laboratory Equipment Calibration: What Every Laboratory Professional Should Know
- Calibration vs Maintenance: Understanding the Difference
- Laboratory Quality Control: A Practical Guide for Beginners
- Laboratory Quality Assurance: Principles, Processes and Best Practices
- Laboratory Documentation and Record Keeping
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References and Further Reading
- World Health Organization (WHO), Laboratory Quality Management System: Handbook
- ISO 15189 — Medical laboratories — Requirements for quality and competence, where applicable
- ISO/IEC 17025 — General requirements for the competence of testing and calibration laboratories, where applicable
- ISO 9001 — Quality management systems — Requirements
- Applicable laboratory regulations and accreditation requirements
- Applicable equipment manufacturer manuals and technical documentation
- Laboratory quality manuals and document-control procedures
Note: Laboratories should use the current editions of applicable standards, regulations and accreditation requirements when developing or reviewing SOPs.
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