Proficiency testing in occupational and environmental health – Current practice and international initiatives for harmonisation

An increasing number of proficiency testing schemes (PT schemes) related to occupational and environmental health have been organised. Most schemes emphasise the importance of the validation of analytical results. With regards to harmonisation of the schemes, there are many differences between the schemes at many levels. These include factors concerning their relationship with legislation, national status, type and quality of proficiency testing material, analytical range and priorities for future development. Since differences between PT schemes have been recognised at the European level by organisers of PT schemes and external quality assessment schemes (EQASs) it seems appropriate to reinforce collaboration between scheme organisers in order to improve the quality of analytical performance in occupational and environmental health.     

玩具油漆涂层中有机锡检测能力验证样品研制及应用分析

制备了用于可迁移有机锡检测能力验证的玩具油漆涂层样品,并开展了相关测定能力验证计划,采用迭代法、四分位法和敏感分析法3种不同统计方法对23家实验室数据进行统计分析,并对不满意结果的原因进行了分析。结果表明所研制样品的均匀性和稳定性良好,能满足能力验证要求。不同统计方法对实验室能力评定结果存在差异,但指定值差异很小,而能力评定标准差差异较大,运用卡方检验能选择出更合理的统计方法。     

Development of a proficiency testing scheme for a limited number of participants in the field of natural water analysis

A proficiency testing (PT) scheme was developed for a limited number of analytical laboratories participating in the analysis of natural water in Israel. Three fit-for-intended-use reference materials (RMs) were prepared for a pilot PT from natural water: RM-blank and two in-house reference materials (IHRMs) with seven analytes fortified to achieve different levels of analyte concentrations. The measurands for the PT participants were the traceable spike values certified in the IHRMs, i.e., added mass concentrations of the analytes. The RM-blank and IHRMs were found to be homogeneous and stable over 11 days, the time necessary for the experimental part of the PT. The RMs were distributed to the PT participants as unknown test items similar to routine samples. The test results were evaluated using their deviations from the IHRM-certified values. Eight Israeli laboratories took part in the interlaboratory comparison. Individual laboratory performance and metrological compatibility of the PT results of the participants, as a local group of laboratories, were evaluated for every analyte.     

Determination of POPs in environmental matrices – proficiency tests for Polish laboratories

Thirty Polish laboratories participated in proficiency tests (PT) for determination of persistent organic pollutants – POPs (PCBs – polychlorinated biphenyls, PAHs – polyaromatic hydrocarbons and pesticides) in solid environmental matrices (sediments, soil). Participants used their in-house method. The aim of the exercises was to obtain information about the “state of the art” of POPs analysis in environmental samples. The CV (coefficient of variation) of analytical results submitted varied from 45 to 65%, with an outlier rate 2 to 7%. The averages of results for all analytes were in good agreement with reference values. Statistical treatment of results was made. Comparison of the each result with the certified values characterizing the material has been done. Additionally, z-scores were calculated taking into account the uncertainty of a certified value and the acceptable deviation from the certified value in the range of −20% to +10% (in accordance with recommendations in the newest directives of European Union (EU) [1]); For rejecting outliers Hampel test has been applied.     

Benefits arising from proficiency testing schemes: The comparison of analytical methods

 The primary objective of proficiency testing (PT) is in the provision of information and support to participating laboratories, to enable them to monitor and improve the quality of their measurements. However, other benefits can be obtained from PT. These include the comparison of data for a given measurement by different methods, the validation of new methods, and the provision of information for laboratories' customers and accreditation bodies. This paper considers the subject of method comparison, and highlights some of the approaches which can be followed, as well as the practical use to which this can be put, to benefit the analytical community more widely. This is illustrated by a case study concerning the measurement of haze in beer. In this study the United Kingdom Institute of Brewing (IoB) conducted a survey of participants in the Brewing Analytes Proficiency Scheme (BAPS). From the survey data taken together with data from the BAPS scheme, the IoB is now in a position to give guidance on the use of particular instruments and procedures, as well as consider changes to the scope of the BAPS scheme to provide greater benefits for participants concerned with measuring haze. Received: 3 March 1998 · Accepted: 9 June 1998     

Role of proficiency testing in monitoring of standardization of hemoglobin A1c methods

After Hemoglobin A_1c (HbA_1c), therapeutic targets for monitoring diabetes therapy were recommended, first, National Glycohemoglobin Standardization Program (NGSP), then, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) developed standardization initiatives. The aim of this article is to demonstrate the role of a proficiency testing (PT) programs in monitoring the long-term effect of these initiatives and the current status of HbA_1c measurement. Measurement precision as a coefficient of variation (CV), measurement bias (bias), and satisfactory HbA_1c result rates in proficiency testing (PT) surveys were evaluated using fresh single donor whole blood PT items and assigned values from a NGSP-certified secondary reference laboratory. Between 2000 and 2010, both CV and bias of the IC measurement method showed a decreasing trend. While the CV of the HPLC measurement method decreased, no significant change was observed in its bias. The rates of satisfactory HbA_1c results in PT surveys were higher in HPLC users than IC users. In 2010, the average CVs in HPLC and IC groups were 2.6 and 3.4?%, biases were 2.7 and 1.8?%, and corresponding total error (TE) estimates were 7.8 and 8.5?%, respectively. These TE values were higher than the maximum permissible measurement error of 7?%, developed based on clinical use of the test. The NGSP and the IFCC networks have promoted improvements in HbA_1c testing; however, tightening of NGSP method certification criteria seems to be necessary to achieve a maximum permissible measurement error of 7?%.     

Key metrological issues in proficiency testing––response to “Metrological compatibility-a key issue in further accreditation” by K. Heydorn

A discussion of proficiency testing (PT) topics started by Heydorn (Accred Qual Assur 15:643–645, 2010) is continued in the present paper. The role of PT in the accreditation of testing/analytical laboratories, the use of consensus values (average or weighted average, median, observed standard deviation, etc.) and a metrological background of PT schemes are discussed. It is shown that metrological traceability, comparability, and compatibility, as well as commutability of a reference material, are the key issues of any PT scheme that applies certified reference material as test items. Metrological compatibility of PT results in such schemes is a property demonstrating the closeness of the PT results to the certified value in comparison with the measurement uncertainty of their difference. The metrological background is especially important for the selection and use of PT schemes for a limited number of participants (fewer than 30) as detailed in IUPAC/CITAC Guide on the topic published in 2010 in Pure Appl Chem 82(5):1099–1135.     

Proficiency testing in the light of a new rationale in metrology

The novel proposed definition of measurement result in the international metrology vocabulary requires a revision of standards and guidelines for proficiency testing (PT), and a new approach to processing proficiency data is needed to test the ability of laboratories to present not only unbiased quantity values, but reliable estimates of their uncertainty. Hence, an accepted reference value with the smallest possible uncertainty is needed to ascertain the proficiency of laboratories reporting results with lower than average uncertainty. A strategy based on the T-statistic is proposed leading to an accepted reference value that fully reflects the uncertainties reported by participants in a PT scheme and permits calculation of E _n numbers to distinguish whether or not measurement results are consistent with the accepted definition of the measurand. The strategy is applied to PT data from a recent international laboratory intercomparison of uranium isotopic ratios.     

A review of proficiency testing scheme in Republic of Korea: in the field of water analysis

For regulatory purposes, it is often required to check the quality of environmental chemical analyses by routine proficiency testing (PT). In this study, the PT scheme of environmental laboratories in Republic of Korea has been reviewed. Especially, real water-based reference materials (RMs) were prepared and distributed for PT schemes. The consensus values from the PT were calculated by robust statistics with its standard uncertainties. The relative bias between the reference values and the consensus values was used as one of the indicators for the determination of the assigned values. The relationship between the performances of the laboratories, expressed by Z scores, and the concentration levels of the RMs were also revealed.     

Enumeration of lactic acid bacteria: lacuna and improvement areas highlighted by proficiency testing

Accreditation and Quality Assurance - During the 2011 to 2018 food microbiology proficiency testing (PT) schemes organized by REQUASUD, a systematic analytical issue was detected. For the...     

A proficiency testing scheme to evaluate the effectiveness of laboratory sample reduction of a soil sample

Accreditation and Quality Assurance - Although proficiency testing (PT) schemes in analytical chemistry are intended to test the entire analytical process, the reality is that some aspects of the...     

The effect of the choice of method for determining assigned value on the assessment of performance in melting point analysis

The determination of melting point is a fundamental test in the Pharmaceutical industry, since it is one of the simplest techniques for the identification of a chemical substance. The melting point provides information on both identity and purity of a chemical substance and for that reason is a key test in the PHARMASSURE proficiency testing (PT) scheme. The PT scheme assesses participant??s determination of melting point, using chemicals of high purity and basing the assigned value on the robust consensus mean (median). In recent rounds, melting point reference standards have been provided as the test material and a reference value used as the assigned value for PT assessment. Comparison of the PT results over a number of rounds, using test materials with a wide range of melting points, shows the overall performance of the participant group is worse in rounds where a reference material and associated reference assigned value are used for performance assessment. When participants were assessed against the reference assigned value, a positive bias was observed in the participant??s results. Detailed information regarding the methodology used demonstrated that the majority of participants use the same analytical method, EU.Ph.2.2.14 (Council of Europe, Strasbourg, 2011), for the determination of melting point although this procedure allows flexibility in key methodological parameters, such as heating ramp rate, which may fail to ensure consistent performance across the group of participant laboratories.     

Comparability and compatibility of proficiency testing results in schemes with a limited number of participants

Comparability and compatibility of proficiency testing (PT) results are discussed for schemes with a limited number of participants (less than 20–30) based on the use of reference materials (RMs) as test items. Since PT results are a kind of measurement/analysis/test result, their comparability is a property conditioned by traceability to measurement standards applied in the measurement process. At the same time, metrological traceability of the certified value of the RM (sent to PT participants as test items) is also important, since the PT results are compared with the RM certified value. The RM position in the calibration hierarchy of measurement standards sets the degree of comparability for PT results, which can be assessed in the scheme. However, this assessment is influenced by commutability (adequacy or match) of the matrix RM used for PT and routine samples. Compatibility of PT results is a characteristic of the collective (group) performance of the laboratories participating in PT that can be expressed as closeness of the distribution of the PT results to the distribution of the RM data. Achieving quality-of-measurement/analysis/test results in the framework of the concept “tested once, accepted everywhere” requires both comparability and compatibility of the test results.     

Proficiency testing schemes for therapeutics and toxicology

 This report addresses the proposition: current proficiency testing (PT) schemes for therapeutics and toxicology can easily engender complacency. The proposition was based on the premise that there are substantial between-laboratory differences and objectives in the supply of services for the measurement of drugs, as a result of which it is difficult to design PT schemes which adequately cover the requirements of all laboratories. Thus, acceptable performance in a PT scheme may lead participants to consider that they have tested their procedures more rigorously than is the case. Four areas, validity of the PT scheme, PT material, frequency of testing and acceptance criteria are examined. Received: 15 April 2000 · Accepted: 15 April 2000     

The role of proficiency testing in the detection and resolution of calibration bias in the LeadCare® blood lead analyzer; limitations of peer-group assessment

Following implementation of the CLIA ‘88 laboratory regulations, the primary role of proficiency testing (external quality assessment, PT) in the U.S. has been widely viewed as one of assuring regulatory compliance. PT can also be an effective tool for detecting widespread analytical problems, subject to limitations based on the method of PT assigned value determination. A recent case study describes the role of two PT programs in detecting and resolving a calibration bias in the LeadCare blood lead analyzer, and illustrates the limitations of peer-group target determination in fulfilling that PT role.     

Preparation of in-house reference material of benzylpenicillin in milk and results of a Brazilian proficiency testing scheme

Two milk test materials containing benzylpenicillin and a benzylpenicillin-free material were prepared and used for the operation of a Brazilian proficiency testing (PT) scheme according to the requirements of ISO/IEC 17043. The PT scheme was designed to include laboratories in charge of confirmatory analysis as well as screening analysis. Sets of sample vials, benzylpenicillin-free and spiked items containing 0.2 g of lyophilized milk, were distributed to each participant. Of 20 participants who reported screening data, 18 accomplished satisfying results, providing evidence of the capability of Brazilian laboratories to produce reliable qualitative information. The assigned value (robust average calculated from 6 results) and its uncertainty were (8.28 ± 0.52) μg/L. Participants’ performance was evaluated using z-scores. A small number of participants were able to report quantitative benzylpenicillin results, and consequently care should be taken in the interpretation of the laboratory’s performance, considering the statistical nature of z-scores. Long-term stability testing on remaining PT items showed that a stable benzylpenicillin quality control material was produced and can be used for internal quality control or validation purposes.     

Performance of commercial soil laboratories in a proficiency test program in Brazil

A soil proficiency test (PT) was administered to 50 participant laboratories in which two sets of samples, consisting of 20 yearly PT samples and 5 ‘blind’ samples in clients’ names were analyzed for pH, organic matter, total acidity, extractable calcium, magnesium, potassium and phosphorus by the laboratories. Our objective was to determine whether laboratories take extra care to analyze clients’ samples as they do with regular PT samples. The analytical data were evaluated essentially by the procedure described in the international harmonized protocol for proficiency testing of analytical chemistry laboratories. Performance of participant laboratories was assessed by z-scores and summary z-scores statistics involving sum of squared z-scores interpreted as chi-square ( c_n² ) \left( {\chi_{n}^{2} } \right) distribution for zero-centered z-scores with unit variance. From 8 750 determinations, outliers and stragglers accounted for less than 2% of the entire data. Over 93% of the data were satisfactory, whereas between 2 and 4% were either unsatisfactory or questionable in both the PT and ‘blind’ tests. On the basis of sum of squared z-scores interpreted from c_n² \chi_{n}^{2} distribution table, between 30 and 40% of the laboratories had more than 90% probability of having their measurement data within the robust mean and standard deviation for each soil parameter, while another 30–42% of the laboratories had less than 50% probability of having measurement data within the robust mean and standard deviation. Overall, 21 laboratories (42%) were ranked in Class A either in the PT or ‘blind’ tests out of which 12 of them (57%) retained this ranking in both tests. Fourteen laboratories (28%) were ranked in Class C in either the PT or ‘blind’ tests with only 5 of them (36%) consistently ranking in this class in both tests.     

Harmonization and transferability of performance assessment: experience from four serum aluminum proficiency testing schemes

Proficiency testing schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. Where several schemes operate in the same analytical sector, there are risks that assessments of performance may be in conflict. Performance assessment for the determination of trace elements such as aluminum in serum is particularly important due to the high risk of contamination and therefore erroneous results. The objectives of this work were (1) to compare several mathematical models to establish a predefined standard deviation for proficiency assessment and (2) to evaluate the influence of instrumental methods and proficiency testing scheme on the assessment of performance for serum aluminum measurements. For this purpose, three samples were sent to the participants of four proficiency testing schemes. Assigned values were calculated according to algorithm A according to ISO 13528 and standard deviation for proficiency assessment according to three methods based on individual variability, state of the art or previous proficiency testing results. The method based on individual variability produced a more stringent standard deviation compared to analytical imprecision based on the state of the art. The instrumental methods gave similar results, whereas significant differences were observed between the four proficiency testing schemes indicating that harmonization of the standard deviation for proficiency assessment fails to allow transferability from one proficiency testing scheme to another and that additional factor(s) contribute to variability in performance assessment.     

Estimates of uncertainty of measurement from proficiency testing data: a case study

The results obtained by a laboratory over a number of proficiency testing/external quality assessment schemes (PT/EQAS) rounds can give information on the uncertainty of its measurements for a given test, provided that conditions such as full coverage of the routine analytical range, traceability, and small uncertainty of the assigned values (compared to the spread of the results) are met and provided that systematic deviations and any other sources of uncertainty are considered. As organisers of the Italian EQAS (ITEQAS) in occupational and environmental laboratory medicine, we tested this hypothesis using as model data from well-performing laboratories taking part in ITEQAS for lead in blood over the last 2 years. We also investigated how different PT/EQAS features (frequency of trials and number of samples) would affect a laboratory estimate of its uncertainty. Such information can be helpful in improving PT/EQAS organisation and define, for a given test: (a) the state of the art of the uncertainty of current measurement procedures, (b) identify needs for improvement of analytical methodologies and (c) set targets for acceptable uncertainty values.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia.Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

CNAL/T0086水溶液pH值测定能力验证分析

2003年5～8月期间,中国实验室国家认可委员会组织了CNAL／T0086水溶液的pH值测定能力验证。本次能力验证由中国实验室国家认可委员会组织,国家标;住物质研究中心负责协调及实施。能力验证的目的是评价各实验室水溶液pH值测定的测试能力和测试水平。对测试结果的统计采用方便并为国际和区域承认的方法——稳健统计法,根据Z比分数评判各实验室的测试结果。