Uncertain about Measurement Uncertainty? Dr Rachel Carling Viapath - - PowerPoint PPT Presentation

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Uncertain about Measurement Uncertainty? Dr Rachel Carling Viapath Guys & ST Thomas NHSFT March 2016

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Uncertain about Measurement Uncertainty?

Dr Rachel Carling Viapath Guys & ST Thomas’ NHSFT March 2016

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  • “Measurement uncertainty is a parameter,

associated with the result of a measurement, (e.g. a test) that defines the range of values that could reasonably be attributed to the measured quantity“ MU for Serum ALP is 300 ± 3 u/L

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  • “The laboratory shall determine measurement uncertainty for each

measurement procedure in the examination phase used to report quantity values on patient's samples. The laboratory shall define the performance requirements for the measurement uncertainty of each measurement procedure and regularly review estimates of measurement uncertainty”

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Qualitative assessment

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* Desirable specification for imprecision which is derived from within subject biological variability Scand J.Clin Lab Invest 1999;59:491-500

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> 2.9#3

Intra batch Inter batch Intermediate precision Inter lab precision Increasing %CV

Minimal variations

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assay technique Variation when the assay is performed on different days As many changes as reasonably possible

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technique Maximum variations

  • n the assay

technique including different laboratories and methods

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> 2.9#3

Intra batch Inter batch Intermediate precision Inter lab precision Increasing %CV 12.5% 4.1% 8.4% 30%

Minimal variations

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technique Maximum variations

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technique including different laboratories and methods

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MU derived from long term in-house IQC data from 2 instruments (n= >100 over 6 month period, MU=2SD) How do we know if this is acceptable? Analytical cut off value is 20% below clinical cut off value No published guidance exists for Target MU EQA scheme of limited utility due to number of participants No traceability

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Acceptable HorRat is 0.3 – 1.3 Data shown for one level of IQC only

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