MEASUREMENT UNCERTAINTY
MU in performance characteristics for assay performance
In an ideal world, manufacturers would provide detailed performance characteristics for assays, including sensitivity, specificity, and the associated MU. We use this information to verify performance when we first put the assays into service, but also as part of our periodic review of examinations. Ideally the performance data provided should clearly state the range of MU expected in all data provided, including clinical accuracy measures and analytical performance, not just an interval CV.
Uncertainty for installation performance and return to service
Upon installation of new equipment, manufacturers must specify the acceptable uncertainty limits for installation performance. These limits should be verified before the equipment is approved for clinical use. Additionally, after preventive or corrective maintenance, manufacturers need to provide clear guidelines on the acceptable MU when returning the equipment to service, so we can accept it. This ensures that the device or instrument remains compliant both with ISO standards and internal quality controls, minimising the risk of patient harm due to instrument errors.
Managing measurement uncertainty and the risk of patient harm ISO 15189:2022 requires laboratories to implement a risk-based approach to quality management. Moving forward application of MU should have mitigating the risk of patient harm as its focus. There are many different risk-based strategies to evidence that this is being considered. For example, using the Failure Mode and Effects Analysis (FMEA) framework, laboratories can assess the potential risks associated with MU in all relevant steps in their processes. FMEA involves identifying failure modes (eg temperature variations in a refrigerator), determining their causes (eg calibration drift), and evaluating the effects on laboratory operations and patient outcomes. By assigning a risk
Digital solutions for IQC management are commonplace, and many integrate MU estimation to automate much of the MU assessment process.
priority number (RPN) based on the severity, occurrence, and detection of each failure, laboratories can prioritise corrective actions. As a simple example, a laboratory identifies that a ±1°C MU limit was not applied to the temperature monitoring of a reagent refrigerator storing critical reagents. Persistently running high at the limit of the range caused reagent degradation, ultimately propagating to patient results. Through FMEA, the laboratory determines that the risk of patient harm is high, and the priority is set to recalibrate the refrigerator more frequently and implement more comprehensive temperature-monitoring systems including incorporating MU into alarm settings.
Another valuable tool is Fault Tree Analysis (FTA), which allows laboratories to map out the potential pathways leading to failure in a process, such as a temperature control system in a freezer. By identifying the root causes of these failures and their potential impacts on patient outcomes, laboratories can develop targeted strategies to reduce risk. In a future series, we will explore how these risk management tools – FMEA and FTA, and others – can be applied more extensively in medical laboratories, providing a structured approach to
An often-overlooked aspect of managing MU in non-assay processes is the requirement for many laboratory devices to be calibrated externally by services accredited to ISO standards
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identifying and controlling measurement uncertainty at every stage of the process.
Increasing use of automation and digital tools One of the key future developments in managing MU is the integration of automation and digital tools. Laboratories are moving toward automated systems to track and control environmental variables like temperature and humidity, as well as to handle calibration processes more effectively. Digital solutions for IQC management are also commonplace, and many integrate MU estimation to automate much of the MU assessment process.
Conclusions Measurement uncertainty is not limited to assay performance in medical laboratories. It extends to various aspects of laboratory operations, from temperature monitoring to environmental controls. By addressing MU in these areas and ensuring external calibration by ISO-accredited services, laboratories can enhance their compliance with ISO 15189 and safeguard patient outcomes. Effectively managing MU, particularly through risk management frameworks like FMEA and FTA, reduces the risk of patient harm and supports the continuous improvement of laboratory processes.
Dr Stephen MacDonald is Principal Clinical Scientist, The Specialist Haemostasis Unit, Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0QQ.
+44 (0)1223 216746. OCTOBER 2024
WWW.PATHOLOGYINPRACTICE.COM
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