EDUCATIONAL GUIDE How to Measure Uncertainty QUALITY CONTROL

How to Measure Uncertainty “The laboratory shall determine measurement uncertainty for each measurement procedure, in the examination phases used to report measured quantity values on patients’ samples. The laboratory shall define the performance requirements for the measurement uncertainty of each measurement procedure and regularly review estimates of measurement uncertainty.” ISO 15189:2012 - Section 5.5.8.3 What is Measurement Uncertainty? Measurement Good Practice Guide No. 11 It relates to the doubt that exists for the result of any measurement. For every measurement there is always a margin...

AACB recommend labs use at least 6 months QC data to calculate uncertainty. When measuring uncertainty we look at two things intra assay precision and inter assay precision. Intra precision refers to precision within a run; it is normally measured by running 20 or more replicates of the same sample at the same time.This process will help to identify any random uncertainties within a test system. Inter precision on the other hand refers to precision over a number of different runs, it is normally measured by running 20 or more replicates of the sample over several days e.g. one replicate every...

Other Factors Affecting Uncertainty It is important to consider bias when calculating uncertainty. Bias must be measured and if it is significant removed or minimised. If bias is not removed the uncertainty of the bias correction must be calculated and included in the overall uncertainty measurement. To calculate the uncertainty of bias we must first determine uRef and uRep. uRef – Uncertainty value of the analyte assigned to the reference material/EQA. This can be obtained from the reference material or EQA report. uRep – Uncertainty value of the analyte in the reference material/EQA when measured...

Conclusion The uncertainty of a measurement relates to the doubt that exists for the result of any measurement. If uncertainty is measured it is no longer uncertainty, but the confidence interval within which the result falls. Uncertainty should be assessed regularly and attempts made to improve the value. Glossary Error – The difference between the measured value and the true value. Uncertainty – A quantification of the doubt relating to a measured value. Standard Deviation (SD) – A measure of how spread out a set of numbers are. Approximately two thirds of all readings will fall between ± one...

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