External quality assessment in clinical chemistry : an examination of requirements, applications and benefits
This thesis describes studies of the requirements, applications and benefits of external quality assessment (EQA) of clinical chemistry laboratories. The involvement of EQA in assessing the analytical quality of results from clinical chemistry laboratories is well-established. This thesis addresses the contribution of EQA in improving clinical chemistry practice and therefore patient care rather than as a method of 'policing' laboratory performance which is the objective of many national EQA schemes. The use of EQA in the assessment of interlaboratory agreement, of analytical methods, of individual laboratory performance, and of quality control and calibration materials is discussed. Surveys are examined as a means to assess the prevailing standard of performance and determine priorities for further EQA to improve performance. The contribution of scoring systems to scheme success by making the information more intelligible to participants is described. The importance of reliable target values is shown, and the reproducibility and accuracy of consensus values in such schemes have been studied. EQA data are shown to be invaluable in providing information on the relative performance of analytical procedures, and on factors such as analyte concentration and laboratory workload which affect performance. The stepwise interpretation of the Variance Index scoring system, and the use of graphical presentations in assisting the assessment of laboratory performance are described. Finally, the use of EQA data in the study of the suitability of quality control materials is examined, with particular reference to their commutability, their use in calibration, and the effects of manufacturing procedures upon their properties. This thesis illustrates the importance of EQA to clinical chemistry practice and to patient care.