MEASUREMENT UNCERTAINTY Role Quality manager Laboratory scientist External auditors Responsibilities


Manage compliance with quality control and ensure corrective actions are managed in an appropriate timeframe


Real-time monitoring of processes from which data are generated to inform MU calculations periodically. Implement corrective actions as necessary


Through unbiased review ensure compliance with accreditation standards and identify areas for improvement


Table 1. A summary of the different aspects of MU review that apply to different stakeholders responsible for the quality performance of the methods.


term imprecision measures, which are a central component of the combined uncertainty. External auditors, such as those


from the United Kingdom Accreditation Service (UKAS) or others depending on your geographic location, provide an objective assessment of the laboratory’s MU practices. Their audits ensure that laboratories adhere to national and international standards, offering recommendations for improvement when necessary.


When should measurement uncertainty be reviewed? This is one of the most common questions about MU, and the answer is: it depends. While this may seem like avoiding providing a definitive answer, it is the only answer that truly reflects the complexities involved. There is no one-size-fits-all solution for how often MU should be reviewed for all assays. Many publications recommend using six months of data for uncertainty of random variability (uRW) estimation. This timeframe, however, may not be appropriate for all tests. High-volume, heavily controlled tests may produce enough data to provide a robust estimate of uRW within six months, but what if the test is only run once a week or once a month? In such cases, different approaches are clearly needed. The best answer is that MU should


be reviewed regularly, with scheduled reviews that are adhered to much like audit schedules – after all, isn’t this just another form of audit? There are, of course, situations where MU must be reviewed on an ad hoc basis. These include instances when significant changes to the assay, analytical platform, or measurement method are implemented. When reviewing data, such changes should be considered as they may introduce or fail to account for significant biases that could lead to different conclusions. Additionally, any time non-conformities


are raised against assay performance, MU should be reviewed. This can provide assurance that the method being brought


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back into service is clinically appropriate. If MU performance cannot be achieved even after non-compliance closure, this should raise serious concerns. This review should be conducted promptly and signed off before patient testing resumes.


Managing excursions from acceptable performance


n Identifying the cause of increased MU


There is an argument that identifying causes of MU deviation from acceptable performance should be straightforward, assuming a full risk-based approach was implemented during the assessment of acceptable performance. This approach would ideally include identifying the likelihood and severity of process failures, a practice increasingly emphasised due to ISO 15189:2022. To determine what has caused the deviation, it is important to use all available tools, with root cause analysis being a commonly used method. However, the correct application of this tool, such as the ‘5 Whys’ methodology, is crucial. Unfortunately, human error is often seen as the root cause, but is it really? If failures are consistently attributed to human error, it may indicate a problem with the root cause analysis process rather than with the staff.


Potential causes of increased MU could include:


Equipment malfunction: Even minor deviations in equipment performance can lead to increased MU. Inadequate calibration: Failing to calibrate equipment correctly or


The challenge with MU is that it is inherently a retrospective measure, reflecting the performance during a previous period of time


frequently enough can introduce significant errors. Environmental factors: Changes in temperature, humidity, or other environmental conditions can affect assay performance.


Reagent variability: Inconsistent quality or storage of reagents can also contribute to increased MU.


n Options for reducing MU to acceptable levels 1. Equipment calibration: Ensure that all equipment is properly calibrated and maintained. Regular calibration checks can prevent discrepancies and ensure accurate results. However, don’t over calibrate to fix QC issues, this will end up altering your traceability chain to being traceable to expected QC performance rather than to higher level standards. If it needs constant recalibration there is probably something more sinister going on. 2. Procedure review: Reassess and refine testing procedures to improve precision and accuracy. Implementing standard operating procedures (SOPs) can help maintain consistent performance. 3. Training and competency: Provide ongoing training for laboratory staff to enhance their skills and ensure they follow best practices. 4. Quality control measures: Implement and review quality control measures, including internal and external proficiency testing, to monitor and improve MU. This is the source of a lot of our MU data so if it isn’t right to begin with any problems may be the processes’ fault rather than the actual assay.


The challenge with MU is that it is inherently a retrospective measure, reflecting the performance during a previous period of time. A significant body of work has focused on mitigating patient harm, prospectively through the correct design of IQC procedures. Recently, and discussed in previous articles in Pathology in Practice, the concept of risk-based QC frequency has been incorporated into laboratory practice. This approach requires a thorough understanding of the potential patient outcomes following a QC event and the period before the next QC run fails. Since we do not know precisely when the QC failure occurred, laboratories must have a local policy for managing patient results tested during the intervening period. Regardless of the approach chosen, it must be fully documented within the local quality management system to ensure that the steps indicated can be taken when required.


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