This post focuses on traceability and stability of control materials in clinical laboratory quality control. Traceability ensures measurement reliability and impacts Measurement Uncertainty (MU). Key steps for traceability include using Certified Reference Materials (CRMs) and verifying performance specifications. Stability, vital for consistent results, is affected by storage conditions, handling procedures, and expiration dates. Both traceability and stability are crucial for accurate MU estimation and reliable laboratory results.

Introduction

This third part of our series focuses on the critical aspects of traceability and stability of control materials used in internal quality control (IQC) in clinical laboratories. Building on the fundamentals discussed in Part 1 and the advanced considerations in Part 2, this post will provide detailed guidance on how to ensure traceability and maintain stability, both of which are essential for accurate Measurement Uncertainty (MU) estimation. For readers interested in practical strategies to mitigate variability and utilise third-party materials effectively, stay tuned for Part 4.

What does traceability mean in the context of laboratory control materials?

Traceability refers to the ability to link measurement results back to a reference standard. It ensures that test results are accurate and comparable over time, which is essential for maintaining high-quality laboratory practices.

Why is stability important for control materials?

Stability is crucial because control materials must consistently perform within expected ranges over their shelf life. Unstable materials can lead to poor performing QC, not reflected in patient results, and therefore rendering the QC results a bit counterproductive!.

How can laboratories ensure the traceability of control materials?

Laboratories can ensure traceability by using certified reference materials (CRMs), regularly verifying performance against reference methods, and maintaining thorough documentation of all traceability processes….in an ideal world – realistically talking to your manufacturers and discussing how they have demonstrated traceability is a better first step!

What factors affect the stability of control materials?

Factors such as storage conditions, handling procedures, and “unrealistic” expiration dates can impact the stability of control materials. Laboratories must follow manufacturer guidelines for storage and handling to maintain stability.

How does the stability of control materials impact Measurement Uncertainty (MU)?

Stability affects MU because any drift or instability in control materials can introduce additional variability through short term biases…..at least in one school of thought although this isnt universally accepted, increasing MU. Consistent, stable control materials help minimise this uncertainty, ensuring more accurate and reliable test results.

Ensuring Traceability of Control Materials

Ensuring traceability of control materials is crucial for maintaining the accuracy and reliability of laboratory results. Traceability refers to the ability to link measurement results back to a standard reference material, ensuring that the results are consistent and comparable over time. While control materials do not need to be Certified Reference Materials (CRM), it is vital that they are traceable to the measurand being tested in patient samples somehow. EQA is often thought to be a check on the traceability chain – but only in schemes where reference methods are used to assign target values – be careful!

Impact of Traceability on MU

Traceability directly impacts MU because it underpins the accuracy and reliability of control materials. If control materials are not traceable, the data used for estimating MU may be compromised, leading to inaccurate or unreliable uncertainty calculations. Therefore, traceability is a cornerstone of reliable MU estimation, as highlighted in ISO/TS 20914:2019. Interestingly traceability is not considered in the total error approach, but thats an argument that rages on.

Steps to Ensure Traceability

Laboratories should follow international standards and best practices for maintaining traceability. Key steps include:

  • Using Certified Reference Materials (CRMs): When available, CRMs should be used as a benchmark to establish traceability. CRMs provide a high degree of accuracy and are essential for calibrating instruments and validating control materials. Often the best we can do are international standards provided by international societies or calibration labs
  • Verifying Performance Specifications: Laboratories should regularly verify the performance specifications of control materials using reference techniques or gold standard methods, again, in an ideal world. This could help ensure that the materials are performing as expected and are suitable for their intended use.
  • Documenting Traceability Processes: Detailed documentation of all processes related to traceability, including the use of CRMs and verification procedures, is essential for regulatory compliance and for supporting quality control efforts…..we can all do that, surely!

Challenges in Achieving Traceability

Despite its importance, achieving traceability can be challenging due to several factors:

  • Availability of CRMs: Not all assays have suitable CRMs available, making it difficult to establish traceability for certain tests.
  • Cost: CRMs and other high-quality reference materials can be expensive, which may be a barrier for some laboratories.
  • Complexity: Establishing traceability requires a thorough understanding of the assay, the control materials, and the reference standards, as well as the ability to implement complex verification procedures.

Maintaining Stability of Control Materials

A fundamental property of control materials is their ability to produce consistent results over time, known as stability. As control materials approach the end of their shelf life, performance can drift, impacting both their accuracy and reliability. Stability is crucial for ensuring that control materials continue to meet the intended specifications throughout their use.

Factors Affecting Stability

Several factors can affect the stability of control materials, including:

  • Storage Conditions: Temperature fluctuations, humidity, and light exposure can all impact the stability of control materials. Proper storage conditions are essential to maintaining stability.
  • Handling Procedures: Incorrect handling, such as improper mixing or exposure to contaminants, can affect the stability of control materials.
  • Expiration Dates: Control materials have a defined shelf life, after which their stability cannot be guaranteed. It is essential to monitor expiration dates and replace control materials as needed.

Impact of Stability on MU

Stability directly impacts MU because unstable control materials can introduce additional variability into the measurement process. This added variability can inflate MU estimates, making them less accurate. By ensuring control materials are stable and perform consistently over time, laboratories can minimise this source of uncertainty, leading to more precise MU calculations and better alignment with ISO/TS 20914:2019 guidelines.

Strategies for Maintaining Stability

To maintain stability, laboratories should implement the following strategies:

  • Regular Stability Testing: Conduct regular stability testing to monitor the performance of control materials over time. This can help identify any changes in performance that may indicate instability.
  • Proper Storage and Handling: Follow manufacturer guidelines for storage and handling to minimise the risk of instability. This includes storing control materials at the recommended temperature and humidity levels and avoiding exposure to light.
  • Lot-to-Lot Consistency: Ensure consistency between different lots of control materials by standardising reconstitution procedures and conducting regular quality checks.

Conclusion

Traceability and stability are foundational aspects of quality control in clinical laboratories. Ensuring that control materials are traceable and stable is essential for accurate MU estimation and reliable laboratory results. Stay tuned for Part 4, where we explore methods to minimise variability and leverage third-party materials to further improve MU management.

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