Performance assessment quality assurance

In the previous section we described several internal methods of quality assessment that provide quantitative estimates of the systematic and random errors present in an analytical system. Now we turn our attention to how this numerical information is incorporated into the written directives of a complete quality assurance program. Two approaches to developing quality assurance programs have been described a prescriptive approach, in which an exact method of quality assessment is prescribed and a performance-based approach, in which any form of quality assessment is acceptable, provided that an acceptable level of statistical control can be demonstrated. 

In a performance-based approach to quality assurance, a laboratory is free to use its experience to determine the best way to gather and monitor quality assessment data. The quality assessment methods remain the same (duplicate samples, blanks, standards, and spike recoveries) since they provide the necessary information about precision and bias. What the laboratory can control, however, is the frequency with which quality assessment samples are analyzed, and the conditions indicating when an analytical system is no longer in a state of statistical control. Furthermore, a performance-based approach to quality assessment allows a laboratory to determine if an analytical system is in danger of drifting out of statistical control. Corrective measures are then taken before further problems develop. 

Using Control Charts for Quality Assurance Control charts play an important role in a performance-based program of quality assurance because they provide an easily interpreted picture of the statistical state of an analytical system. Quality assessment samples such as blanks, standards, and spike recoveries can be monitored with property control charts. A precision control chart can be used to monitor duplicate samples. 

Once a control chart is in use, new quality assessment data should be added at a rate sufficient to ensure that the system remains in statistical control. As with prescriptive approaches to quality assurance, when a quality assessment sample is found to be out of statistical control, all samples analyzed since the last successful verification of statistical control must be reanalyzed. The advantage of a performance-based approach to quality assurance is that a laboratory may use its experience, guided by control charts, to determine the frequency for collecting quality assessment samples. When the system is stable, quality assessment samples can be acquired less frequently. 

Quality Assurance/Quality Control parameter and metrics to ensure data reproducibility, e.g. the establishment of calibrated RNA samples and reference datasets to objectively assess the performance of different microarray platforms (see also MAQC project http //w w w.nature. com/nbt/focus/maqc/). 

The program quality assurance plan may need periodic or emergency revisions Ongoing review of the data should reveal whether any deficiencies are due to Inadequate performance of vendors or to defects In the quality assurance plan Defects In the plan could result from Inadequate quality assessment techniques If measured levels of contaminants were significantly different from anticipated levels, for example ... 

Twenty-eight of fifty-four samples purchased were found to have coatings made from polyester resins and so their contents were analysed for TPA and IPA. Analysis was by GC-MS after extraction and derivatisation to form the dimethyl esters of TPA and IPA. Included in the analytical quality assurance steps taken was participation in a check-sample exercise whereby four samples were supplied by a second laboratory and analysed blind. The performance of the testing laboratory was assessed from the accuracy and precision of their measurements and was demonstrated to be acceptable. 

It is generally recognized and accepted that analytical methods must be suitable for the intended use. Furthermore, EU Directives 85/591/EEC, 89/397/EEC and 93/99/ EEC state that analytical procedures for compliance testing with food laws are to be carried out on the basis of validated methods. Method validation is known as the process used to confirm that a procedure is fit for a particular analytical purpose. This process, an essential part of analytical quality assurance, can be described as the set of tests used to establish and document performance characteristics of a method. The performance characteristics of a method are experimentally derived values for the fundamental parameters of importance in assessing the suitability of the method (Horwitz 1988, 1995 Thompson and Wood 1993, 1995 Eurachem 1996 FAO 1998 US EPA 1995 US FDA 1993a). These parameters include ... 

A Proficiency Test (PT) is defined as the study of laboratory performance by means of ongoing interlaboratory test comparisons . It is also known as an external quality assessment scheme, external laboratory performance check or external quality assurance (EQA). There are many such schemes run by independent external bodies for different analytes in a variety of matrices. Evidence in published papers shows that the performance of analytical laboratories improves as a result of participating in Proficiency Testing schemes and the betw een-laboratory precision can improve, sometimes dramatically. This is especially true in the early years of participation. 

In order for the report and evidence presented in court to be of value, a regular programme of quality assurance must be entered into by the analyst and his laboratory. Records of the methods used should be available, along with documented assessments of the performances of each of the tests and instruments used. Such records are essential should the functionality of the tests or equipment be challenged. 

The principles and concepts of TQM have been formalized into a quality management process, as illustrated in Figure 19-3. The traditional framework for managing quality in a healthcare laboratory has emphasized the establishment of quality laboratory processes (QLPs), QC, and quality assessment (QA). A QLP includes analytical processes and the general poHcies, practices, and procedures that define how all aspects of the work get done. QC emphasizes statistical control procedures but also includes nonstatistical check procedures, such as linearity checks, reagent and standard checks, and temperature monitors. QA, as currently applied, is primarily concerned with broader measures and monitors of laboratory performance, such as turnaround time, specimen identification, patient identification, and test utility. Quality assessment is the proper name for diese activities rather than quality assurance. Measuring performance does not by itself improve performance and often does not detect problems in time to prevent harmful effects. Quality... 

Collaborative drug therapy management is most successful when the nature of the collaborative arrangement, the competencies and credentialing required, and the quality assurance checks that will be used to assess performance are defined at the outset in each specific setting. 

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