In part 1 of a 4 part series, this post explores selecting control materials for internal quality control in clinical laboratories. It also looks at their impact on Measurement Uncertainty (MU). The Statistical Quality Control (SQC) process is crucial for ensuring lab results meet quality standards. Control materials can be assayed, unassayed, in-house, or third-party, each with specific benefits and considerations. Choosing the right control material is critical for managing MU, with implications for clinical decision intervals/levels. Consider lab requirements, cost, validation, and documentation when selecting control materials for effective quality control.
Introduction
An appropriately designed Statistical Quality Control (SQC) process is essential. It ensures that medical laboratory results meet the intended quality standards. According to ISO 15189:2012 and more recently the 2022 version), laboratories must ensure their SQC processes are robust enough to detect when performance is stable, identify when it is becoming unstable, and minimise the risk of reporting incorrect patient results. A key component is selecting the correct control material. This first part of our series will cover the fundamental characteristics of control materials, the importance of traceability, and how these factors influence Measurement Uncertainty (MU) in clinical laboratory settings. For those interested in deeper explorations, be sure to read the subsequent parts of this series.
What is internal quality control (IQC) in clinical laboratories?
IQC refers to the procedures used by laboratories to ensure the accuracy and reliability of their test results. It involves using control materials to monitor the performance of testing systems regularly, detecting errors, and ensuring results are consistent and dependable.
Why is it important to choose the correct control materials for IQC?
Selecting appropriate control materials is crucial because they help identify issues with test accuracy and precision. Using the right materials ensures that the test results are reliable and meet the necessary clinical standards, which is vital for patient care.
What types of control materials are commonly used in clinical laboratories?
Common types of control materials include assayed controls (with known values), unassayed controls (without pre-assigned values), in-house controls (developed within the lab), and third-party controls (independent from test kit manufacturers). Each type serves different purposes based on the laboratory’s needs.
How often should control materials be tested in a laboratory setting?
Control materials should be tested according to the laboratory’s quality control plan. The frequency can vary depending on the test type, the volume of tests conducted, and regulatory requirements. Most importantly it is based on minimising the risk of clinical harm through an uncontrolled situation going undetected
How do control materials impact Measurement Uncertainty (MU)?
Control materials directly influence MU as they are the basis of determining imprecision using the top-down method. Consistent use of reliable control materials helps in accurately calculating MU.
Understanding Control Materials in Clinical Laboratories
Control materials are defined as any fresh, frozen, stabilised solution, or lyophilised preparation used to monitor a test system. These materials are central to all QC processes in pathology laboratories. However, no single control material can cover all assay types, and the same assay may require different control materials depending on the technology used. Control materials for quantitative assays often come with expected values and ranges, but these should be verified locally to ensure they reflect the specific performance of the system being tested. Qualitative controls, on the other hand, are typically assigned as either positive or negative, indicating the presence or absence of a particular measurand.
When selecting control materials, it is crucial to consider the characteristics of the assay you intend to control. Despite the variety of control materials available, all must meet certain common features to be effective. These features directly impact MU, as consistent and accurate control materials reduce variability and improve the reliability of MU estimates. By using well-characterised control materials, laboratories can better estimate MU in line with ISO/TS 20914:2019, ensuring that MU calculations accurately reflect the performance of the test systems in use.
Types of Control Materials
Control materials can be broadly categorised into assayed, unassayed, in-house, and third-party materials:
Assayed Controls
These are control materials that come with manufacturer-provided expected values and ranges. They are often used for standardisation across multiple laboratories. However, they may not always reflect the specific conditions of every lab, which is why local verification of these controls is necessary.
Unassayed Controls
These do not come with manufacturer-specified values. Instead, they must be validated within the laboratory to establish their own control ranges. This validation process allows laboratories to tailor control materials to their specific needs but requires rigorous testing and documentation.
In-House Controls
Created within the laboratory, these controls are designed to match closely with the patient samples being tested. They are often used when specific commercial controls are not available or when cost constraints prevent the purchase of commercial controls.
Third-Party Controls
These controls are developed independently of the assay’s manufacturer. They provide an unbiased assessment of assay performance and can be particularly valuable in detecting shifts in performance that might be missed with manufacturer-provided controls.
Impact of Control Material Selection on Measurement Uncertainty (MU)
Choosing the right control material is critical in managing MU in laboratory testing. MU is a parameter that describes the range within which the true value of a measurand lies, taking into account all possible sources of error in the measurement process.
| Control type | Considerations |
| Assayed Controls | Often provide a good starting point for MU estimation, but they need local verification to ensure they are appropriate for the specific instruments and conditions of the laboratory. |
| Unassayed Controls | Require extensive local validation, which can provide a more accurate representation of MU under specific laboratory conditions but demands significant resources and expertise. |
| In-House Controls | Allow for the closest match to patient samples, potentially reducing MU by aligning control materials more closely with test conditions. However, creating and validating in-house controls can be resource-intensive. |
| Third-Party Controls | Offer an independent check on assay performance, which can help identify and correct biases that might otherwise increase MU. |
Measuring Limits and Clinical Decision Intervals/Levels
Good laboratory practice dictates using at least two levels of quality control: typically representing normal and abnormal states. However, this may not always be sufficient. Assays are used for various purposes, from diagnosis to long-term treatment monitoring, and controlling them effectively means considering both clinical and analytical performance. Ideally, assays should be controlled at all clinical decision points where treatment interventions are influenced, as well as at points where analytical specifications, such as linearity limits and limits of detection, need to be met.
Controlling assays at these various points is crucial for managing MU, as it helps define the range over which the laboratory can reliably measure and report results. By implementing IQC at key decision intervals, laboratories can better manage the analytical performance and thus reduce the uncertainty associated with measurements. This approach aligns with ISO/TS 20914:2019’s recommendations for a top-down MU assessment, where data from routine IQC procedures are used to estimate uncertainty across the entire range of clinical decisions.
For a deeper dive into how different clinical decision points and assay characteristics impact MU, check out Part 2 of this series, where we explore advanced considerations for control materials.
Practical Tips for Selecting Control Materials
When selecting control materials, consider the following:
Lab Requirements
Understand the specific needs of your laboratory, including the range of tests performed and the levels of precision required.
Cost vs. Benefit
Weigh the cost of commercial control materials against the benefits of potentially lower MU and higher accuracy. In some cases, investing in high-quality controls can reduce overall costs by decreasing the need for repeat testing.
Validation Process
Ensure that control materials are validated under local conditions to provide accurate and reliable data for MU estimation.
Documentation and Compliance
Maintain thorough documentation of all validation and verification processes to comply with regulatory requirements and support quality control efforts.
Conclusion
Selecting the right control material is fundamental to ensuring quality in laboratory testing. By understanding the basics of control materials, including their characteristics and how they influence MU, laboratories can implement more effective quality control processes. Stay tuned for Part 2, where we discuss advanced considerations in choosing control materials for IQC.
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