Quality assessment schemes

RSD of 40-60% at 1 / mol/L (27 g/L) and 20% at 4 / mol/L (108 jwg/L) have been commonly observed (Taylor et al., 1986 Taylor, 1990). It Is unclear what the reasons are for this poor performance. Methodology of itself does not seem to be a key factor, since most laboratories have been using similar methodology based on graphite furnace atomic absorption spectrometry. The most important factor appears to be the experience of the laboratory carrying out the analysis. For some schemes, there has been a dramatic rise in the number of participants, mostly of laboratories with very little previous experience of trace element analysis (Taylor, 1990). With the exception of a number of experienced laboratories, the performance of a large number of laboratories is insufficient to allow a proper assessment of aluminium exposure (Taylor, 1990). The performance of laboratories has also been impeded by the lack of suitable reference materials, particularly in the case of water and dialysis fluid. 

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External quality assessment schemes involve the distribution by the organizer, to participating laboratories, of aliquots from the same sample. Participants analyze the received specimen and send the results back to the organizer who prepares a report to summarize all data. 

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. 

Morisi G, Menditto A, Patriarca M, Taylor A, eds. (1996) European external quality assessment schemes in occupational and environmental medicine. Ann 1st Sup di Sanita 32(2) i9i-3i6. 

Taylor A (1996) Reference materials and analytical standards to stimulate improved laboratory performance Experience from the external quality assessment scheme for trace elements in biological samples. Mikrochim Acta 123 251-260. 

Proficiency testing is a special type of laboratory performance studies defined as study of laboratory performance by means of ongoing interlaboratory test comparisons (ISO Guide 33 [1989] ISO/REMCO N 280 [1993] IUPAC [1993] Prichard et al. [2001]). Proficiency testing is an essential part of external quality assessment schemes and performance checks. 

Keith D. Miller, Chief Scientific Officer, UCL-Advanced Diagnostics, Cancer Institute, Director of the UK National External Quality Assessment Scheme for Immunocytochemistry In-situ Hybridisation and, Fellow of the Institute of Biomedical Science, London, UK... 

The belief in some quarters that patients have proprietary rights over their samples and any information generated therefrom, and that even anonymised data should not be divulged without permission may cause difficulties even for routine services with no overt research brief, putting interlaboratory audits and external quality assessment schemes at risk. 

Heinrich-Rumm, R., G. Lehnert, and J. Angerer. 1996. The German external quality assessment scheme in occupational and environmental medicine. Ann. 1st. Super Sanita. 22(2)12 47-251. 

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. 

The reports provided to participants in external quality assessment schemes should contain a munb of important values. As illustrated in Fig. 5, most schemes include data such as the number of participants accepted in the final analysis, the mmiber rejected, i.e. the outliers, the mean and standard deviation of the accepted results, the spiked value together with the individual participant s value and its standard deviation interval (si) from the consensus mean. In addition, a computerised frequency distribution histogram is generally provided. 

Fig. 5. A typical computerised printout issued on a monthly basis to participants in an external quality assessment scheme <<<< represents the position of the reported value of the individual laboratory in relation to the reported values of other...

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. 

Wales External Quality Assessment Scheme www.weqas.co.uk (e.g., urinalysis program). 

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). 

Uncertainty Estimation from External Quality Assessment Schemes... 

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. 

Guildford Trace Elements External Quality Assessment Scheme (TEQUAS)... 

Two types of quality assessment schemes can be distinguished external quality assessment (between laboratories) and internal quality control (within laboratories Hunter et al., 1980). The principal... 

Quality assessment schemes aim to establish whether or not the test results are within accepted limits and to demonstrate the possible necessity to correct test design (Batty, 1977). 

National External Quality Assessment Scheme in Clinical Chemistry. Review 1987-1989. Bioresearch Ireland — EOLAS, Dublin, Ireland. 

Taylor A, Briggs RJ and Cevik C (1994) Findings of an external quality assessment scheme for determining aluminum in dialysis fluids and water. Clin Chem 40 1517-1521. 

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... 

To aid control procedures, many laboratories participate in external quality assessment schemes (also termed external proficiency testing). In these assessment schemes, the pools of material may be human or animal in origin and are distributed to a number of participating laboratories for comparative purposes. Given the various analyzer technologies, it is perhaps not surprising that results obtained by various analyzers differ to some extent and these proficiency schemes do alert laboratories to poor performance. 

American Association of Clinical Chemistry (AACC)/College of American Pathologists U.K. External Quality Assessment Scheme for PbB analyses + 60 fig/L if value is < 400 ftg/L + 15% if value is a 400/ig/L Depends on variance index score 4-16... 

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