Abstract
Standardisation of laboratory medicine and clinical chemistry applications enables the comparison of measurements that are performed at two different laboratories, in different locations and at different times. Therefore, it allows hospital laboratories to improve the accuracy of results and consequently provide better patient care. The first step to measurement standardisation of small molecules in biological samples is having a higher-order reference measurement procedure (RMP) and higher-order certified reference materials (CRMs) to achieve traceability to the SI unit. This research investigates the sources of variability and uncertainty in the development and application of higher-order RMPs and CRMs for two clinical applications. These two applications provide an extensive evaluation of the standardisation approach because 1) of the molecular weight up to about 1000 Da, these molecules cover the two ends of the molecular weight range of small molecules,2) and the nature of the compounds is rather different; being endogenous polar vs. exogenous non-polar 3) additionally they are measured in two different matrices. These case study applications are metanephrines (m/z 167-197) in plasma and tacrolimus (m/z 804) in whole blood. Both applications in this research need standardisation because they suffer from high variability among laboratories as demonstrated by external quality assurance schemes (EQAS).The key characteristics of reference measurements are traceability to the SI unit and low measurement uncertainty estimates. In this work, novel candidate higher-order RMPs and CRMs were developed to provide the cornerstone for the standardisation of these two applications. The work described developed candidate higher-order RMPs using liquid chromatography tandem mass spectrometry (LC-MS/MS) with the double exact-match isotope dilution (DEM-IDMS) calibration approach. This thesis investigates the sources of variability and uncertainty along with the challenges to developing RMPs and CRMs to the level of accuracy, precision and traceability required to achieve higher-order reference measurements. These RMPs were applied to assign reference values to a candidate higher-order CRM, underpinning the comparison of hospital laboratories’ measurements of tacrolimus. The tacrolimus in pooled patient blood CRM that is characterised in this work is the first higher-order CRM to be produced where tacrolimus is incurred rather than spiked onto blank blood as is the case of other commercially available materials. Similarly, the RMP of plasma metanephrines is the first candidate higher-order RMP that will be submitted for listing on the Joint Committee for Traceability in Laboratory Medicine and Clinical Chemistry (JCTLM) database. Furthermore, the developed RMPs and CRMs were used for the assessment of a novel micro-sampling technique to demonstrate other areas of application of RMPs and CRMs.
The assignment of reference values by RMP and the use higher-order CRMs support: a) EQAS laboratories to perform better; b) global initiatives towards standardisation of best clinical practice guidelines; c) establishing diagnostic reference ranges; d) production of secondary CRMs; e) assigning measurement uncertainty estimates to secondary methods and f) providing a traceable standard to attain measurement traceability. Ultimately, standardisation of laboratory medicine and clinical chemistry applications aims to improve patient health care and quality of life.
| Date of Award | 1 Aug 2021 |
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| Original language | English |
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| Supervisor | Leon Barron (Supervisor), David Cowan (Supervisor), Vincenzo Abbate (Supervisor), Chris Hopley (Supervisor) & Mark Parkin (Supervisor) |