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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.15, #6)


Strategies to set global analytical quality specifications in laboratory medicine: 10 years on from the Stockholm consensus conference by Per Hyltoft Petersen; Callum G. Fraser (pp. 323-330).
The setting of analytical quality specifications in laboratory medicine has attracted attention for many years. Over time, many strategies were advocated and all had advantages and disadvantages. In the final decade of the last millennium, considerable confusion existed on how to define analytical quality specifications correctly and how to apply them in everyday practice. This led to wide professional interest. In 1999, a consensus conference sponsored by IUPAC, IFCC and WHO was held in Stockholm on “Strategies to Set Global Analytical Quality Specifications in Laboratory Medicine”. The consensus set useful and well-documented strategies for the setting of analytical quality specifications into a hierarchy with the best strategy at the highest level, namely, (1) Evaluation of the effect of analytical performance on clinical outcomes in specific clinical situations, (2) Evaluation of the effect of analytical performance on clinical decisions in general, (3) Published professional recommendations, (4) Performance goals set by regulatory bodies and EQAS organisers, and (5) Goals based on the current state of the art. Much success has been achieved since the promulgation of the statement with the approach being adopted by many in laboratory medicine for a very wide variety of purposes, particularly in quality management. However, there is a requirement for additional investigation of, inter alia, quality specifications for examinations done on measurements performed on ordinal and nominal scales, pre-analytical factors and matrix effects, examinations done as POCT, target values of control materials, and ways in which analytical quality specifications can be used both to set what is the optimum performance and as a tool for assessment of everyday practice.

Keywords: Analytical bias and imprecision; Analytical goals; Analytical requirements; Laboratory medicine; Matrix effects; Point-of-care-testing


Some metrological aspects of ordinal measurements by Emil Bashkansky; Tamar Gadrich (pp. 331-336).
Although some measurements can be made on any scale (including a continual scale), cost and speed considerations sometimes tip the scales toward using ordinal measurements. This paper presents a way to evaluate classical metrological characteristics, such as error, uncertainty and precision of single and repeated measurements based on the legitimate basic operations for ordinal data. The only legitimate measurement operations among ordinal variables are limited to equal or greater than/less than, the usual assessment measures such as average, standard deviation cannot be applied. Consequently, in order to receive reliable results and draw valid conclusions from ordinal measurements it is essential to develop and use only the appropriate methods.

Keywords: Ordinal scale; Error; Uncertainty; Repeatability and reproducibility; Repeated measurements


Purity verification and measurement uncertainty by Siu Kay Wong (pp. 337-341).
In chemical analysis, laboratories are required to verify the purity of reference material being used. Also, the contributions from the verification procedure, where significant, have to be included in the estimation of the total measurement uncertainties of the test results. One common verification procedure is to use another source of the same material if an appropriate certified reference material were not available. This involves a comparison test where the purity value of the reference standard is determined using a second source reference standard as the “calibrant”. In normal practice, the standard uncertainty of the purity value of a reference standard is estimated according to the probability distribution function (PDF) of the possible purity values of the reference standard concerned. With the use of Monte Carlo simulation technique, this paper attempted to study the effect of verification process on that PDF and thus the associated standard uncertainty as well. Also, the effects of parameters like the purity of the second source reference standard, the method precision and the acceptable range set for the comparison test on the verification outcome were discussed.

Keywords: Purity verification; Monte Carlo simulation; Measurement uncertainty


Challenges in the accurate speciation analysis of selenium in humans: first report on indicative levels of selenoproteins in a serum certified reference material for total selenium (BCR-637) by Petru Jitaru; Marco Roman; Carlo Barbante; Sophie Vaslin-Reimann; Paola Fisicaro (pp. 343-350).
Se is one of the most investigated essential trace elements in the past years, mostly due to its cancer prevention properties. Nevertheless, the accurate determination of its biologically active species, such as the selenoproteins (SeProt) in human serum, is currently a challenging task. This is because of the lack of appropriate quantification standards, certified reference materials (CRMs), and/or reference measurement methods. Additionally, most of the methods developed so far for the determination of SeProt were applied to the analysis of control (volunteers) serums, which are not available to other laboratories, therefore making methods inter-comparison virtually impossible. We present here for the first time indicative levels of SeProt in a commercially available human serum, namely the BCR-637 CRM with certified level of total Se. The concentrations of selenium associated with glutathione peroxidase (GPx), selenoprotein P (SelP) and selenoalbumin (SeAlb) in this serum were calculated using the results obtained by 13 different analytical methods (literature and non-published data) on the basis of (affinity) high-performance liquid chromatography (AF-HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). The indicative levels of SeProt in the BCR-637 serum can be used for validation of methods dealing with the determination of these proteins in human serum.

Keywords: Human serum; Certified reference material; BCR-637; Selenoproteins; Indicative concentrations


The multivariate coefficient of variation for comparing serum protein electrophoresis techniques in external quality assessment schemes by Lixin Zhang; Stéphanie Albarède; Gilles Dumont; Christel Van Campenhout; Jean-Claude Libeer; Adelin Albert (pp. 351-357).
External quality assessment (EQA) schemes are national or transnational programmes designed to control the analytical performance of clinical laboratories and to maintain inter-laboratory variability within acceptable limits. In such EQA programmes, participants are usually grouped by the type of assay technique/equipment they use. The coefficient of variation (CV) is a simple tool for comparing the inter-laboratory reproducibility of such techniques: the lower the CV, the better the analytical performance. Serum protein electrophoresis, a laboratory test profile consisting of five fractions (albumin, α 1, α 2, β and γ globulins) summing up to 100% of total proteins, can also be assayed in different ways depending on the media or the analytical principle. We propose a multivariate CV for comparing the performance of electrophoretic techniques in EQA, thus extending the univariate CV concept. First, the compositional nature of electrophoretic data requires a one-to-one transformation from the five-dimensional to the four-dimensional space. Next, robust estimations of the mean and the covariance matrix are needed to avoid the effect of outliers. The new approach is illustrated on electrophoretic datasets from the French and Belgian national EQA programmes.

Keywords: Analytical variability; Electrophoretic techniques; EQA schemes; Equipment performance; Reproducibility; Test profiles


Standardisation of a European measurement method for the determination of mercury in deposition: results of the field trial campaign and determination of a measurement uncertainty and working range by Richard James Christopher Brown; N. Pirrone; C. van Hoek; M. Horvat; J. Kotnik; I. Wangberg; W. T. Corns; E. Bieber; F. Sprovieri (pp. 359-366).
A standard method for the measurement of mercury in deposition is currently being finalised by Working Group 25 of the European Committee for Standardisation’s Technical Committee 264 ‘Air Quality’, in response to the requirements of the European Union’s Fourth Air Quality Daughter Directive. This paper reports the results of a field measurement programme which was undertaken to assess the uncertainty of the proposed standard method, define its working range and determine its compliance with the required data quality objectives of the Fourth Air Quality Daughter Directive.

Keywords: Deposition; Mercury; Air quality; Field trial; Standardisation; Uncertainty

European analytical column no. 38 (January 2010) by EuCheMS-DAC by Bo Karlberg; Paul Worsfold; Jens E. T. Andersen (pp. 367-371).
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