MEASUREMENT UNCERTAINTY
Even slight variations in temperature or exposure to light can cause degradation. Reagents stored at 2–8°C, for example, may degrade faster if the refrigerator’s temperature fluctuates due to uncertainty in the monitoring system. If a constant high or low temperature is present at the limits of the range, but not exceeding the limits, this may cause problems with reagent performance. For example, a reagent stored in a refrigerator with a temperature set at 4°C but with an MU of ±1°C degrades more quickly than anticipated. Excess troubleshooting of IQC performance may result. Of course, commutability of IQC to patient samples may also not be consistent, so patient results may be worst affected. The same could happen with environmental conditions such as humidity and air pressure that can affect the performance of sensitive instruments or reagents. High humidity can damage electronic components, and air pressure fluctuations can impact incubators or other pressure- sensitive equipment. Monitoring these environmental aspects is less well established in laboratories, but is something that should be risk assessed if it is considered important.
Pipette calibration
Calibration of pipettes takes into account both the accuracy of the dispensed volume but also the variability between measurements. If making up reagents or IQC and the dispensed volume is either inaccurate or too variable, we will be introducing variability into final results that is not inherent to the method, but rather the preparation method.
Measurement uncertainty is frequently discussed in the context of assays, but laboratories often overlook its importance in non-assay processes
This has consequences particularly if making up quality-control material (lyophilised material being reconstituted, for example) when patient samples are being tested without preparation. IQC will give a falsely high MU estimate, potentially affecting clinical interpretation and confidence in results, or worse… the laboratory itself. It is now an established best practice to regularly have all pipettes serviced by an accredited calibration service, and performing small- scale reviews of performance locally between these calibrations. Once this is performed, don’t forget acceptability criteria for bringing the equipment back into service as well.
External calibration of laboratory equipment
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. These external services provide laboratories with confidence that their equipment meets the necessary precision and accuracy required under ISO 15189. Many laboratories are unfamiliar with the specific ISO standards governing the calibration services they rely on. It is crucial that any service
providers performing calibration on laboratory equipment are accredited to the appropriate standard. This external verification helps ensure that the MU associated with equipment, such as thermometers or pipettes, is adequately managed. Neglecting to use accredited services can introduce uncontrolled sources of uncertainty into laboratory processes, increasing the risk of compromised results and patient harm. Therefore, external calibration by accredited bodies is not only a compliance requirement but also a safeguard against risk.
What does the future hold for MU?
Although the following are considerations of MU in assay performance they are aspects that largely are out of the laboratory’s control, for now. Manufacturers play a pivotal role in ensuring that medical laboratories can effectively manage MU throughout various stages of equipment and assay use. For compliance to ISO 15189 we require manufacturers to provide clear and precise information about MU to assist laboratories in maintaining accurate and reliable operations. This is a work in progress as far as it being provided to us in the laboratory.
WWW.PATHOLOGYINPRACTICE.COM OCTOBER 2024
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