Is linearity the same as calibration verification?

No. Although the two processes are closely related, they serve different purposes.

Calibration verification confirms that assay performance remains acceptable at representative points across the reportable range, typically including low, mid-range and high concentrations.

Linearity testing evaluates whether the relationship between measured response and analyte concentration remains proportional throughout the analytical measurement range using multiple concentration levels.

In many laboratories, appropriately designed multi-level linearity studies may be used to support calibration verification requirements when they demonstrate acceptable performance across the reportable range and meet laboratory-defined criteria.

Why do laboratories perform calibration verification and linearity testing together?

Many laboratories combine calibration verification and linearity assessments to:

• Verify reportable range performance
• Support AMR studies
• Demonstrate assay performance across multiple concentration levels
• Improve inspection readiness
• Streamline validation workflows

Our calibration verification and linearity materials are designed to help laboratories perform both activities efficiently while generating reliable and well-documented performance data.

Calibration versus calibration verification

Although these terms are often used together, they serve different purposes within laboratory quality management programmes.

When is calibration verification required?

Under CLIA requirements and many accreditation programmes, laboratories typically perform calibration verification at least every six months and whenever events occur that could affect analytical performance, including:

• Scheduled six-month verification intervals
• Introduction of reagent lots that could affect the reportable range
• Major instrument maintenance, repair or replacement of critical components
• Significant quality control shifts, trends or unexpected results
• Method modifications or AMR verification activities

Maintaining documented calibration verification records is an important component of laboratory quality management and inspection preparedness.

How to perform calibration verification?

1. Select appropriate materials: Choose an appropriate, ready-to-use product (such as VALIDATE®) that covers your assay's specific reportable range and closely matches the patient matrix.  
2. Verify system readiness: Confirm that instrument maintenance has been completed and quality control results are within established limits. 
3. Run and compare results: Analyse all material levels as patient samples and compare measured values with assigned concentrations and laboratory acceptance criteria. 
4. Evaluate performance across the AMR: Assess performance across the reportable range using appropriate statistical methods, such as CLSI EP06 guidance where applicable. 

5. Document and investigate: Record all results, acceptance limits, and material details. Investigate and resolve any results that fall outside established criteria before routine testing resumes. 

Setting and interpreting acceptable limits  

Acceptance limits should be established using regulatory requirements, laboratory quality goals, allowable total error specifications, manufacturer recommendations and clinical performance expectations. 

During calibration verification, measured results are compared with assigned target values across the reportable range. If results remain within predefined acceptance limits, calibration performance can be considered verified. Results outside established limits should be investigated and appropriate corrective action taken before routine patient testing resumes. 

Well-defined and documented acceptance criteria help laboratories maintain compliance and confidence in reported patient results. 

How accreditation programmes approach calibration verification?

Regulatory and accreditation organisations may use different terminology, but their overall objective is similar: ensuring laboratories can demonstrate reliable analytical performance across the reportable range and maintain documented evidence of ongoing test system accuracy.

Key areas commonly reviewed during inspections include:

• Verification of performance across the reportable range
• Appropriate use of calibration verification materials
• Established acceptance criteria
• Investigation of out-of-specification results
• Complete and traceable documentation
• Evidence of ongoing quality management activities

Laboratories should always follow the specific requirements of their accrediting organisation and internal quality procedures.

How to select calibration verification materials ?

Choosing suitable calibration verification materials can simplify workflows and support reliable assessment of assay performance. Consider the following factors when selecting materials:

• Analyte coverage: Choose materials that support the analytes within your testing menu. 
• AMR coverage: Select materials that provide multiple concentration levels across the reportable range. 
• Matrix compatibility: Use materials that closely resemble patient samples to minimise matrix-related effects. 
• Ready-to-use format: Liquid materials can reduce preparation time and minimise handling errors. 
• Documentation support: Comprehensive documentation can support compliance and inspection readiness.