Quality assessment external measures

Measurements of individual laboratory performance provides for comparisons between laboratories. It then follows to ask why some laboratories report data that are more accurate and precise than do their peers, and a well designed external quality assessment scheme allows investigation of some of the important factors (see below). A comparison of performance between individual laboratories also helps to stimulate those who are not so successful to improve (or abandon the assay) and those who do well to continue with their expertise. Finally, changes of performance may be monitored as a consequence of some new factor, e.g. purchase of a new piece of equipment, work carried out by a different analyst, change to the methodology etc. 

Quality control describes the measures used to ensure the quality of individual results or a batch of results. The measures used will vary according to the particular application. It is a means of evaluating the current performance of the method being used and the general procedures used in the laboratory. There are two types of quality control, namely internal quality control and external quality assessment. These are covered in detail in Chapters 6 and 7, respectively. 

Some important assays commonly used in biochemical genetics laboratories do not provide quantitative data (e.g. MPS-EP, qualitative urinary organic acid analysis, AA-TLC). In addition, all successful investigations depend heavily upon selection of the correct analytes to measure and the appropriate interpretation of the quantitative or qualitative results in their clinical context. These challenges suggest a requirement for external quality assessment or proficiency testing schemes that can inform participants about their performance in these areas when compared with other centres. 

Where possible, there should be participation in external quality assessment ( proficiency testing ) using material with reference measurement values. 

Table 3 Acceptance limits set by external quality assessment (EQA) organizers for inorganic components in human serum based on biological variations and the potential of routine methods and observed ranges in the International Measurement Evaluation Programme (IMEP)-7 Evaluation Programme [5]...

Keywords Traceability Clinical chemistry Reference measurement procedure Isotope dilution mass spectrometry (IDMS) External quality assessment... 

For non-SI traceable quantities the predominant objective must be an agreement on the definition of these quantities on an international basis before reference measurement procedures can be developed and used for assigning target values in external quality assessment. 

Propagation of errors using isotope dilution ICP-MS has been considered to determine how to optimize the measurements [201]. Comparison of analysis results from external calibration versus isotope dilution can be used to assess the quality of external calibration results and the effectiveness of internal standards with external calibration [202,203]. Because isotope ratio precision depends on the total ion count rate, the use of high-efficiency sample introduction to generate larger signals can improve isotope ratio precision and, therefore, analysis precision [204]. 

If participants in an external quality assessment scheme simply receive the results and check the performance index or some other measure to see if it is satisfactory, a great deal of valuable information is lost. Data from these schemes offer an opportunity to study a laboratory s assay and to assist in the education of laboratory personnel. Simple graphical approaches can be used that do not require complicated calculations. If a laboratory has a computer, more elaborate calculations can be carried out. Basically, the participating laboratory has analysed a sample for a particular analyte and has then to compare the value found with the True value. Possible estimates of the True value include the overall mean for all participants, the method mean, the mean value obtained by designated reference laboratories, or a stated spiked value. Some schemes provide all these values, but the majority provide an overall mean, which will be used in the following discussion. The overall mean has limitations if the technique for elimination of outliers is unsatisfactory or if a particular method, which causes a marked bias at certain concentrations in the overall mean, is used by a significant number of laboratories. 

Repeatability closeness of agreement between results of successive measurements carried out under the same conditions (i.e., corresponding to within-run precision). Reproducibility closeness of agreement between results of measurements performed under changed conditions of measurements (e.g., time, operators, calibrators, and reagent lots). Two specifications of reproducibility are often used total or between-run precision in the laboratory, often termed intermediate precision and interlaboratory precision (e.g., as observed m external quality assessment schemes [EQAS]) (see Table 14-2). 

HuUin DA, McGrane MTG. Effect of bilirubin on uricase-peroxidase coupled reactions. Implications for urate measurement in clinical samples and external quality assessment schemes. Ann Clin Biochem 1991 28 98-100. 

The direct measurement of plasma phylloquinone is probably the best indicator of vitamin K status and has been shown to correlate well with intalce. HPLC methods have been reviewed, and typically require 0.5 to 2,0mL of serum or plasma. Protein precipitation and lipid extraction (often into hexane), followed by solvent evaporation preparative HPLC (to isolate vitamin K from other lipids) reevaporation of the vitamin K-rich fraction dilution in the mobile phase and further HPLC, with either electrochemical or fluorometric detection often after postcolumn reduction, are required. Typical between-batch imprecision values are coefficient of variation (CV)s of 11% to 18% with limits of detection of lower than 50pmol/L. An external quality assessment scheme (EQAS) is avafiable in the UK. 

Fig. 1.3, The quality spiral described in Fig. 1,1 and its implementation depend on the tools available in the laboratory. These tools concern laboratory structure, personnel, management, external and internal quality assessment measures. The proper use of the available tools will lead to the development of the quality objectives (adapted from ref [10]).

A number of commercially available assays are now available for some common laboratory animals (e.g., mouse, rat, and dog). These assays are based on chemiluminescence, enzyme linked immunosorbent (ELISA) colorimetric assays, and radioimmunoassay. For the iodothyronines (e.g., total Tj and TJ, a wide choice of assays designed for human samples is available these can be used across species because the molecule structures are common (Anderson, Nixon, and Akasha 1988 Daminet et al. 1999 Mooney, Shiel, and Dixon 2008). Some assays require adjustments to ensure that the majority of samples are measured within a suitable range because the plasma values vary across the species (Table 10.2.1). When these assays are used, there may be problems associated with calibration materials because external quality assessment schemes continue to show minor and sometimes major differences between assays produced for hormone analyses. With all of these immunoassays, the reagents must be shown to be suitable for the species being studied. Reports of... 

External quality assessment Many countries have authoritative, regular, structured provision for EQA for at least general clinical laboratory work (biochemistry, hematology, microbiology). There are also large numbers of specialist EQA schemes, often international, for those analytes measured in fewer laboratories. In addition, schemes to monitor... 

A quality control programme is the procedure employed to ensure that the analysis continuously meets the goal for imprecision and accuracy. Several external quality control programmes exist for measurement of cobalamin, e.g. United Kingdom National External Quality Assessment Service (www.ukneqas.org.uk). 

In the previous chapter, it was established that in industry, plant hazards can cause harm to property (plant—machinery, asset), people, or the environment. So, it is important to develop some means of analyzing these and come up with a solution. Unfortunately, it is not as straightforward as it sounds. There are plenty of plant hazard analysis (PHA) techniques and each of them has certain strengths and weaknesses. Also each specific plant and associated hazard has specific requirements to be matched so that hazard analysis will be effective. In this chapter, various hazards (in generic terms) will be examined to judge their importance, conditions, quality, etc. so that out of so many techniques available for PHA it is possible to select which one is better (not the best because that needs to be done by experts specifically for the concerned plant) suited for the type of plant. So, discussion will be more toward evaluation of PHA techniques. Some PHA is more suited for process safety management (PSM) and is sometimes more applicable for internal fault effects [e.g., hazard and operability study (HAZOP)]. In contrast, hazard identification (HAZID) is applicable for other plants, especially for the identification of external effects and maj or incidents. HAZID is also covered in this chapter. As a continuation of the same discussion, it will be better to look at various aspects of risk analysis with preliminary ideas already developed in the previous chapter. In risk analysis risk assessment, control measures for safety management systems (SMSs) will be discussed to complete the topic. 

A useftil applicadon of time-dependent PL is the assessment of the quality of thin III-V semiconductor alloy layers and interfaces, such as those used in the fabri-cadon of diode lasers. For example, at room temperature, a diode laser made with high-quality materials may show a slow decay of the acdve region PL over several ns, whereas in low-quality materials nonradiative centers (e.g., oxygen) at die cladding interface can rapidly deplete the free-carder population, resulting in much shorter decay times. Measurements of lifetime are significandy less dependent on external condidons than is the PL intensity. 

It is important to issue a common understanding on the topics of method validation, traceability, and uncertainty of measurements. Here, the interrelationships between method validation, traceability, and MU of results will be elucidated. Throughout the landscape of guidelines and standards, the most relevant information is selected, compiled, and summarized. Great importance is attached to the different method performance parameters and their definitions, ways of expression, and approaches for practical assessment. We discuss the role of method validation within QA as well as the topics of standardization, internal and external quality control (IQC and EQC, respectively), and accreditation and the links between these different aspects. 

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