VDSP Reference Measurement System: The Role of Accuracy ... · Mean inter-laboratory imprecision...
Transcript of VDSP Reference Measurement System: The Role of Accuracy ... · Mean inter-laboratory imprecision...
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VDSP Reference Measurement System: The Role of Accuracy-Based EQA/PT
Schemes
Graham Carter Imperial College Health Care NHS Trust
www.deqas.org
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DEQAS and the VDSP
• The ODS has funded NIST to assign values to DEQAS samples.
• DEQAS is an ‘accuracy’ based Proficiency
Testing scheme (from April 2013)
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The Role of Accuracy based 25-OHD EQA/PT Schemes
To monitor over time: • The accuracy of individual results • Inter-laboratory imprecision • Trueness of 25-OHD methods EQA/PT samples must be commutable
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Accuracy of results: DEQAS sample 440 (July 2013)
Target value 48.4 nmol/L (ALTM 51.3 nmol/L)
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DEQAS October 2012; Effect on Mean % Bias of Switching Performance target from ALTM to NIST assigned values
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DEQAS results; October 2012 –July 2013
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ALTM vs NIST; October 2012 –July 2013
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Mean inter-laboratory imprecision (CV%) of 25OHD results; distribution cycles since 1995
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Use of a common standard by LC-MS/MS users; effect on inter-laboratory imprecision (CV%)
Total 25-OHD
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Use of a common standard in LC-MS/MS assays – effect on inter-laboratory imprecision (CV%)
25-OHD3
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326 327 328 329 330 C1 C2
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In-house standards Chromsystems standard
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Suggested Assay Performance Limits Based on Biological Variation*
*Stöckl D et al. Clin Chim Acta 2009;408:8-13
Measurements CV (%) Bias (%) Reference Labs ≤ 5% ≤ 1.7% “Routine” Labs ≤ 10% ≤ 5%
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25-OHD Methods; % of users submitting results within the suggested bias limits of ± 5% (Sample 436, July 2013)
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Trueness (%Bias) of automated Competitive Binding Assays for 25-OHD (1)
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Trueness (% Bias) of automated Competitive Binding Assays for 25-OHD (2)
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Trueness (% Bias) of LC-MS/MS and HPLC/UV
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Imprecision of automated Competitive Binding Assays for 25-OHD (1)
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Imprecision of automated Competitive Binding Assays for 25-OHD (2)
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Imprecision of LC-MS/MS and HPLC/UV
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Summary • The VDSP is designed to standardize 25-OHD
results to the true value (RMP) • Accuracy based PT schemes can (should?) be
used to monitor: • Accuracy of individual 25-OHD results • Inter-laboratory imprecision • Trueness of 25-OHD methods
But can we ever guarantee the accuracy of an
individual result?
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Thank you!
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Acknowledgements
• DEQAS: Jayne Shannon, Julia Jones
• ODS: Christopher Sempos, Paul Coates
• NIST: Johanna Camara, Lane Sander, Karen Phinney, Stephen Wise,
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DEQAS: an accuracy based Proficiency Testing Scheme for 25-OHD assays
Aim of DEQAS is to monitor/improve performance of 25-OHD assays through:
• Quarterly distribution of unadulterated human serum samples (from haemochromatosis patients).
• Calculation of %Bias from a Target value (ALTM until January 2013, NIST values from April 2013)
• Educational/investigative exercises