Biochemistry
External quality assessment schemes for inorganic elements in the clinical laboratory: Lessons from the OELM scheme

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Abstract

Measurements of inorganic elements in clinical laboratories produce results used for the diagnosis, the treatment and the monitoring of deficiencies or overloads. The main objective of External Quality Assessment Schemes is to verify, on a regular frequency, that clinical laboratory results correspond to the quality requirement for patient care. Therefore, External Quality Assessment Schemes represent an essential component of a laboratory’s quality management system. However, External Quality Assessment Schemes within the same analytical field remain heterogeneous for different reasons such as samples, determination of assigned value, acceptable limits, content of the reports. The aim of this review was to describe and illustrate some major critical aspects of External Quality Assessment Schemes based on Occupational and Environmental Laboratory Medicine external quality assessment scheme experience.

Introduction

Inorganic trace element results produced by clinical laboratories are used to diagnose and treat deficiencies or overloads, and to monitor patients or exposed workers. The main objectives of External Quality Assessment schemes (EQA), also call Proficiency Testing programs (PT) or interlaboratory comparisons (ILC) are to verify, on a regular frequency, that laboratory results correspond to the quality requirement for patient care, to improve result transferability among laboratories whatever the analytical method used and to detect analytical errors [[1], [2], [3], [4]]. Consequently, participation in EQA allows laboratories to implement corrective actions, when necessary, to improve analytical data, and represents an essential component of a laboratory’s quality management system. Participation in EQA is a requirement for laboratory accreditation according to International Organisation for Standardisation (ISO) 15189 [1,[3], [4], [5], [6]]. Two ISO standards give information on how to conduct these schemes and interpret their results. ISO/IEC 17043 describes the technical and managerial requirements to be fulfilled by competent providers whereas ISO 13528 describes statistical methods to analyse the data obtained as well as recommendations for the interpretation of results by participants and by accreditation bodies [7,8]. However, EQA schemes within the same analytical field remain heterogeneous as demonstrated for lead in whole blood [9]. Many factors explain this heterogeneity, particularly sample commutability, determination of assigned value and acceptable limits, analytical factors accessed in the reports, number of participants [1,3,4,6,[9], [10], [11], [12]]. Consequently, participation in EQA does not guarantee its effectiveness.

The aims of this review were to describe some major critical aspects of EQA which allow to evaluate the value of EQA and to give clues on how the EQA result should be interpreted by participating laboratories. Examples based on occupational and environmental laboratory medicine (OELM) EQA experience illustrate these different aspects [13]. More detailed information is found in the different cited references.

Section snippets

EQA description

The different steps of EQA are summarized in Fig. 1. Briefly, EQA samples are periodically sent by a provider to a group of laboratories for a given set of analyses. The participating laboratories do not know the concentrations of the analytes. Each laboratory treats the samples according to instructions for participants and performs measurements theoretically as for patient samples [4]. However, it is known that some laboratories treat EQA samples as special [6,14,15]. Then, participants

Samples properties

The provider is responsible for the preparation and validation of commutable, homogeneous and stable samples with concentrations within the range observed in the clinical laboratories [3,19] which may represent a serious challenge. In the field of inorganic elements, the range of concentrations must ideally cover from severe deficient levels of essential trace elements to toxic levels of all elements as laboratories analyse samples from hospitalized patients, general population, environmental

Quality specification determination

One of the major issues for EQA organizers is the choice of quality specifications (QS), in other word the limits around the assigned value used for classifying laboratory results as satisfactory or unsatisfactory [2,7,10,11]. It also defines the standard deviation for proficiency assessment (SDPA), determined as 0.5 QS. SDPA is used to calculate participants’ performance in term of z score and the acceptable standard uncertainty of the assigned value (ux) determined as 0.3 SDPA. QS depends on

Assigned value determination

The determination of assigned value is also a major issue, as the performance of individual laboratory is estimated by comparing their results with the assigned values. According to ISO 13528, assigned values can be determined by different ways [3,8,10] and examples have been previously reported for Cu, Se and Zn in serum [3,8,10,47]. The most accurate is to measure the concentrations of the inorganic elements using methods of higher metrological order, such as isotope dilution mass

Reporting concentrations outside the linear range

Another problem encountered by EQA organizers is the reporting of results for concentrations outside the linear range of the method. Indeed, statistics for determining assigned values are based on measured numerical values. Therefore, results outside the linear range of the method cannot be introduced properly whatever the solution used. When a concentration is higher than the linear range, the participant either does not submit its result or uses a higher dilution that may change the matrix.

Interpretation of the results

As stated in EQA description paragraph, the organizer delivers a report to each participant at the end of each run. Most of EQA organizers estimate analytical performance by the determination of z score which is the distance from laboratory results to the assigned value divided by the SDPA.Zscore=(LaboratoryresultAssignedvalue)/SDPA

In cases where the uncertainty of the assigned value is not negligible (that is ux > 0.3 SDPA), the organizer can take this into account using the z’ score

Interaction between organizer and participant

The organizer must also reply to the questions and claims of the participants and send regularly satisfaction questionnaires in order to improve its EQA. Inappropriate shipment (i.e. delay, damage of the package) may affect the stability of the samples. It is important to check the appearance of sample quality and physical integrity at reception as well as to verify the sample labelling. If something is wrong, the EQA provider must be contacted for the replacement of the sample(s) [3].

Conclusion

In conclusion EQA represents an indispensable tool for monitoring laboratory performance and more generally for laboratory quality assurance management. But this statement is true only if samples are commutable, assigned values are accurate and quality specifications fit for clinical needs.

A strong relationship between providers of similar EQA samples is highly recommended for improving the standardization and harmonization of laboratory performance evaluation as well as for sharing samples and

Funding sources

This review did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

The authors are either employees from public institutions (J Arnaud, I De Graaf, MB Fofou-Caillierez, M González-Estecha, M Patriarca, V Patriarca, M Ropert-Bouchet, L Schröer-Janssen, C Siebelder, M Te Winkel, C Weykamp) or from non-governmental non-profit associations (MC González Gómez, M Ventura Alemany). They do not receive any financial support linked to the OELM

Declaration of Competing Interest

The authors are either employees from public institutions (J Arnaud, I De Graaf, MB Fofou-Caillierez, M González-Estecha, M Patriarca, V Patriarca, M Ropert-Bouchet, L Schröer-Janssen, C Siebelder, M Te Winkel, C Weykamp) or from non-governmental non-profit associations (MC González Gómez, M Ventura Alemany). They do not receive any financial support linked to the OELM scheme. The participating laboratory annual fees are managed by a public institution in Italy: Istituto Superiore di Sanita

Acknowledgements

We are very grateful to the present and past members of the OELM board as well as to the present and past participants of the OELM EQA and of the “Organizers of external quality assessment / proficiency testing schemes related to occupational and environmental medicine” Network.

References (54)

  • T. Badrick et al.

    Can a combination of average of normals and "real time" External Quality Assurance replace Internal Quality Control?

    Clin. Chem. Lab. Med.

    (2018)
  • ISO/IEC 17043

    Conformity Assessment – General Requirements for Proficiency Testing

    (2010)
  • ISO 13528

    Statistical Methods for Use in Proficiency Testing by Interlaboratory Comparison

    (2015)
  • G.R.D. Jones et al.

    EFLM Task Finish Group - Analytical Performance Specifications for EQAS (TFG-APSEQA). Analytical performance specifications for external quality assessment - definitions and descriptions

    Clin. Chem. Lab. Med.

    (2017)
  • M. Panteghini et al.

    Task Force on Performance Specifications in Laboratory Medicine of the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM). Strategies to define performance specifications in laboratory medicine: 3 years on from the Milan Strategic Conference

    Clin. Chem. Lab. Med.

    (2017)
  • F. Ceriotti et al.

    Harmonization of External Quality Assessment Schemes and their role - clinical chemistry and beyond

    Clin. Chem. Lab. Med.

    (2018)
  • Occupational and Environmental Laboratory Medicine

    (2019)
  • M.A. Noble

    Does external evaluation of laboratories improve patient safety?

    Clin. Chem. Lab. Med.

    (2007)
  • W. Punyalack et al.

    Finding best practice in internal quality control procedures using external quality assurance performance

    Clin. Chem. Lab. Med.

    (2018)
  • G. Matar et al.

    Uncertainty in measurement for 43 biochemistry, immunoassay, and hemostasis routine analytes evaluated by a method using only external quality assessment data

    Clin. Chem. Lab. Med.

    (2015)
  • A. Padoan et al.

    An approach for estimating measurement uncertainty in medical laboratories using data from long-term quality control and external quality assessment schemes

    Clin. Chem. Lab. Med.

    (2017)
  • EEE-PT Working Group (EA-Eurolab-Eurachem)

    EQALM (European Organisation for External Quality Assurance Programmes in Laboratory Medicine), Selection, Use and Interpretation of Proficiency Testing (PT) Schemes

    (2011)
  • R.F. Greaves

    The central role of external quality assurance in harmonisation and standardisation for laboratory medicine

    Clin. Chem. Lab. Med.

    (2017)
  • W.G. Miller et al.

    Recommendations for assessing commutability part 1: general experimental design

    Clin. Chem.

    (2018)
  • G. Nilsson et al.

    Recommendations for assessing commutability part 2: using the difference in Bias between a reference material and clinical samples

    Clin. Chem.

    (2018)
  • J.R. Budd et al.

    Recommendations for assessing commutability part 3: using the calibration effectiveness of a reference material

    Clin. Chem.

    (2018)
  • P.J. Parsons et al.

    Determination of total mercury in urine by inductively coupled plasma mass spectrometry (ICP-MS)

    Plasma Source Mass Spectrometry: Current Trends and Future Developments.

    (2005)
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    All the authors are members of the scientific advisory board of “Occupational and environmental laboratory medicine (OELM) external quality assessment/proficiency testing schemes”. The MCA laboratory team prepares the samples (responsibles: Marieke Te Winkel and Cas Weykamp) according to the decision of the board, is responsible of the website management (Irene de Graaf) and of the quality assurance management (Liesbeth Schröer-Janssen). The authors are also members of the network “Organizers of external quality assessment / proficiency testing schemes related to occupational and environmental medicine”. This network includes organisers of inorganic element external quality assessment schemes from different countries in Europe, North America and Asia and its aim is focused on the harmonization and improvement of trace element external quality assessment schemes.

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