First proficiency testing to evaluate the ability of European Union National Reference Laboratories to detect staphylococcal enterotoxins in milk products

The European Commission has designed a network of European Union-National Reference Laboratories (EU-NRLs), coordinated by a Community Reference Laboratory (CRL), for control of hygiene of milk and milk products (Council Directive 92/46/ECC). As a common contaminant of milk and milk products such as cheese, staphylococcal enterotoxins are often involved in human outbreaks and should be monitored regularly. The main tasks of the EU-CRLs were to select and transfer to the EU-NRLs a reference method for detection of enterotoxins, and to set up proficiency testing to evaluate the competency of the European laboratory network. The first interlaboratory exercise was performed on samples of freeze-dried cheese inoculated with 2 levels of staphylococcal enterotoxins (0.1 and 0.25 ng/g) and on an uninoculated control. These levels were chosen considering the EU regulation for staphylococcal enterotoxins in milk and milk products and the limit of detection of the enzyme-linked immunosorbent assay test recommended in the reference method. The trial was conducted according to the recommendations of ISO Guide 43. Results produced by laboratories were compiled and compared through statistical analysis. Except for data from 2 laboratories for the uninoculated control and cheese inoculated at 0.1 ng/g, all laboratories produced satisfactory results, showing the ability of the EU-NRL network to monitor the enterotoxin contaminant.     

French laboratory proficiency testing program for food microbiology

The proficiency testing program in food microbiology (Réseau d'Analyses et d'Echanges en Microbiologie des Aliments; RAEMA), created in 1988, currently includes 440 participating laboratories. The program establishes proficiency in detection of Salmonella and Listeria monocytogenes, as well as quantitation of aerobic microorganisms, Enterobacteriaceae, coliforms, Escherichia coli, Clostridium perfringens, coagulase-positive Staphylococcus, and Listeria monocytogenes. Twice a year, 5 test samples are sent to participants to assess their precision and trueness for enumeration and detection of microorganisms. Results show an increasing involvement of food microbiology laboratories in quality assurance programs and use of standard and validated analytical methods. However, the percentage of laboratories obtaining questionable and unsatisfactory microbiological results remains relatively constant.     

Laboratory assessment by combined z score values in proficiency tests: experience gained through the European Union proficiency tests for pesticide residues in fruits and vegetables

The obligation for accredited laboratories to participate in proficiency tests under ISO 17025, performing multiresidue methods (MRMs) for pesticide residues, involves the reporting of a large number of individual z scores making the evaluation of the overall performance of the laboratories difficult. It entails, time and again, the need for ways to summarise the laboratory’s overall assessment into a unique combined index. In addition, the need for ways to continually evaluate the performance of the laboratory over the years is equally acknowledged. For these reasons, following 14 years of the European Union Reference Laboratory for Pesticide Residues in Fruits and Vegetables (EUPT-FV), useful formulas have been designed to globally evaluate the assessment of the participating laboratories. The aim is to achieve a formula which is easy to understand, which can be applied and which fits the purposes of long-term evaluation detecting positive and negative trends. Moreover, consideration is needed for a fair compensation of bad results in MRM, taking into account the large number of compounds that are covered. It is therefore important to be aware of the difficulties in getting satisfactory values from a wide range of compounds. This work presents an evaluation of the main well-established combined z score formulas together with those new ones developed here which have been applied to the European proficiency test results (EUPTs) over the years. Previous formulas such as the rescaled sum of z score (RSZ), the sum squared of z score (SSZ) and the relative laboratory performance (RLP) are compared with the newer ones: the sum of weighted z scores (SWZ) and the sum of squared z scores (SZ2). By means of formula comparisons, conclusions on the advantages, drawbacks and the most fit-for-purpose approach are achieved.     

Blood lead proficiency testing: overview of the federally sponsored program in the U.S.

External proficiency testing is a proven method for improving the quality of laboratory measurements, including lead in blood. Several proficiency testing programs exist to fill this need. This article describes the U.S. federally sponsored Blood Lead Proficiency Testing Program. Three specimens, composed of blood from dosed cows, are distributed to participants each month. Target values are determined by a group of 10 referee laboratories. Participant performance has shown steady improvement over time.     

The proficiency testing programme for trace elements of the CORILA project

Harmonised quality schemes are being implemented in the framework of the thematic area Organization and Dissemination of Data of the Consorzio per la Gestione del Centro di Coordinamento delle Attività di Ricerca Inerenti il Sistema Lagunare di Venezia (Consortium for the Management of the Coordination Centre of Research Activities on the Venice Lagoon System, CORILA). Over the last 2 years, two proficiency tests were completed at the time of writing (while a third one is still in progress) to assess the capabilities of the analytical laboratories involved in the determination of trace elements in environmental inorganic matrices from the Lagoon of Venice.Both interlaboratorial trials were based on the determination of As, Cd, Cr, Cu, Fe, Hg, Pb and Zn in aqueous acidic, matrix-enriched solutions at concentrations within the ranges generally found in marine water and in sediment after chemical digestion, respectively. The proficiency of participants was assessed on the basis of the z score criterion (|z|≤2, acceptable results; 2<|z|<3, questionable results; |z|≥3, unacceptable results). In the two trials, the relevant percentages for the laboratories scoring |z|≤2 and |z|<3 were 61% and 71% and 65% and 77%, respectively. These first two proficiency tests, on the one hand, clearly pointed to the benefits the laboratories had from their participation in these exercises, and on the other hand, provided sound evidence of the need for further trials based on real environmental matrices.     

The practice of proficiency testing in China

This paper briefly summarises the current situation for proficiency testing (PT) in China, outlines the policy for PT of China’s national accreditation committee for laboratories (CNACL), and exemplifies activities of the CNACL’s metal working group. Received: 9 December 2000 Accepted: 14 December 2000     

The role of proficiency testing in method validation

The general principle of using data collected during proficiency testing (PT) for the additional purpose of assessing method performance is discussed. Particular attention is paid to the similarities and differences in conduct of traditional interlaboratory method performance studies and proficiency testing. Recommendations are made for implementing PT-based method performance studies, including statistical assessment of the data. It is concluded that, properly implemented, PT-based method performance study provides essentially equivalent information to that obtained from traditional collaborative study and may be used in appraising candidate methods with a view to their adoption as standard methods.     

Application of a new AMIQAS computer program for integrated quality control, method evaluation and proficiency testing

Summary The computer program AMI - Quality Assessment Scheme (AMIQAS) was designed to give easy statistical management of analytical data in relation to method evaluation, internal quality control and proficiency testing. The program is designed in accordance with the recommendation of the ISO 5725 guideline and other official recommendations. The program consists of a database, test for outliers, statistics and graphs for evaluation of an analytical method for chemical, biological and environmental analysis, different control charts to be used in day-to-day internal quality control (Shewhart charts and z-charts). Finally the program has facilities to perform proficiency testing (also called external quality control) and produce the relevant evaluation reports for the documentation of method performance and quality control of results of measurements. The present paper demonstrates the applicability of the AMIQAS program for integrated method evaluation, internal quality control and proficiency testing using the determination of the concentration of lead in human whole blood as the numerical example.     

Laboratory proficiency testing of aflatoxins in corn and peanuts--a cooperative project between Thailand and the United States

The objective of this project was to conduct an aflatoxin proficiency test program in government, academia, and industry laboratories in Thailand. Aflatoxin-free corn and peanuts and corn and peanuts naturally contaminated with aflatoxins diluted to approximately 25 micrograms/kg were analyzed. Homogeneity of prepared, naturally contaminated test samples was checked on multiple replicates. The test was conducted according to the ISO/IUPAC/AOAC INTERNATIONAL Harmonized Protocol with z scores indicating laboratory performance. The participants used 3 methods: enzyme-linked immunosorbent assay, thin-layer chromatography, and the minicolumn. Of 19 laboratories that reported results for aflatoxins in naturally contaminated corn, 13 (68%) performed satisfactorily, on the basis of the mean obtained by an expert laboratory, a calculated target value for standard deviation, and the z score. Of 21 laboratories that reported results for aflatoxins in naturally contaminated peanuts, 10 (48%) performed satisfactorily. For aflatoxin-free corn, 6 laboratories reported finding aflatoxins at > or = 10 ng/g, chiefly by the minicolumn method; for aflatoxin-free peanuts, 1 laboratory reported finding aflatoxins at > 10 ng/g. Subsequently, a workshop of lectures and laboratory sessions was conducted to improve performance. A new and simple successive outlier removal procedure applied to the same data removed the same laboratories as did the use of z scores.     

Long-term proficiency testing for the UK Acid Waters Monitoring Network

A series of proficiency test rounds to support the UK Acid Waters Monitoring Network has been conducted since the inception of the Network in 1988. These tests provide an illustration of the accuracy and comparability of analysis for laboratories that supply data to the Network. A summary of the tests is reported. Performance with respect to accuracy targets defined for the Network has been shown to be satisfactory for the majority of measurands of interest in studies of surface water acidification.     

A comparison of performance statistics for proficiency testing programmes

Recently, ISO issued a new document on statistical methods for use in proficiency-testing schemes. The document presented a number of new performance statistics that involve the use of measurement uncertainties of the participants’ results and/or the assigned values for the performance evaluation. Making use of the Monte Carlo simulation technique, this paper attempts to compare selected performance statistics of different approaches. In addition, the simulation programme was extended to study the effect of multi-modality in participants’ results on the performance evaluation when different performance statistics were applied.     

Establishment of proficiency testing programs in the Philippines

Accreditation and Quality Assurance - In order to improve the competitiveness of Philippine food products in the global market, the Department of Science and Technology—Food and Nutrition...     

Experiences from the assessment of proficiency testing providers

Following a pilot project in 2001–2002, UKAS accredited nine PT providers. During the course of the pilot and at subsequent surveillance visits, UKAS has gained experience in assessing organisations against the criteria detailed within ISO/IEC Guide 43-1:1997 and ILAC G13:2000. This article explores some of the key aspects that arose during the pilot and how UKAS has accommodated the addition of the accreditation of PT providers in to its range of services.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Preparation of items for a textile proficiency testing scheme

Accreditation and Quality Assurance - One of the fundamental stages in planning and developing any interlaboratory comparison is the selection and preparation of the test items to be distributed to...     

The proof of analytical chemical education lies in proficiency testing: A proficiency testing programme in polytechnic academia and vocational colleges in The Netherlands

Participation in proficiency testing schemes (PT-schemes) is an important way to prove and to improve the skills of analytical chemical students. It gives valuable information on the professional capabilities of the students and is thus an important step in the training of laboratory engineers and technicians. In the programme described three types of samples are offered to the students: chemical, environmental and clinical samples. A guiding protocol presents instructions to the participating student groups. Standard operating procedures are available, but the students are also free to select their own method. The results are methodologically and statistically judged by professional PT-organisers and are presented in the customary way: the dataset, the mean (consensus) value of all participants and the Z-scores. The final presentation of the results takes place in an annual symposium where awards are presented to the best performing student groups, and a lecture programme is presented with subjects in the area of quality assurance and quality control. A selection of results from the KILO/PT/1998–1999 and the KILO/PT/1999–2000 programme is presented.     

The proof of analytical chemical education lies in proficiency testing: a proficiency testing programme in polytechnic academia and vocational colleges in The Netherlands

Participation in proficiency testing schemes (PT-schemes) is an important way to prove and to improve the skills of analytical chemical students. It gives valuable information on the professional capabilities of the students and is thus an important step in the training of laboratory engineers and technicians. In the programme described three types of samples are offered to the students: chemical, environmental and clinical samples. A guiding protocol presents instructions to the participating student groups. Standard operating procedures are available, but the students are also free to select their own method. The results are methodologically and statistically judged by professional PT-organisers and are presented in the customary way: the dataset, the mean (consensus) value of all participants and the Z-scores. The final presentation of the results takes place in an annual symposium where awards are presented to the best performing student groups, and a lecture programme is presented with subjects in the area of quality assurance and quality control. A selection of results from the KILO/PT/1998-1999 and the KILO/PT/1999-2000 programme is presented.     

An error model for evaluation and interpretation of proficiency testing

Data from proficiency testing can be used to increase our knowledge of the performance of populations of laboratories, individual laboratories and different measurement methods. To support the evaluation and interpretation of results from proficiency testing an error model containing different random and systematic components is presented. From a single round of a proficiency testing scheme the total variation in a population of laboratories can be estimated. With results from several rounds the random variation can be separated into a laboratory and time component and for individual laboratories it is then also possible to evaluate stability and bias in relation to the population mean. By comparing results from laboratories using different methods systematic differences between methods may be indicated. By using results from several rounds a systematic difference can be partitioned into two components: a common systematic difference, possibly depending on the level, and a sample-specific component. It is essential to distinguish between these two components as the former may be eliminated by a correction while the latter must be treated as a random component in the evaluation of uncertainty. Received: 20 November 2000 Accepted: 3 January 2001     

An anti E. coli O157:H7 antibody-immobilized microcantilever for the detection of Escherichia coli (E. coli).

A silicon microcantilever sensor was developed for the detection of Escherichia coli O157:H7. The microcantilever was modified by anti-E. coli O157:H7 antibodies on the silicon surface of the cantilever. When the aquaria E. coli O157:H7 positive sample is injected into the fluid cell where the microcantilever is held, the microcantilever bends upon the recognition of the E. coli O157:H7 antigen by the antibodies on the surface of the microcantilever. A negative control sample that does not contain E. coli O157:H7 antigen did not cause any bending of the microcantilever. The detection limit of the sensor was 1 x 10(6) cfu/mL when the assay time was < 2 h.     

Analytical performance is improved by regular participation in proficiency testing: an analysis of data from the Aquacheck proficiency testing scheme

Analysis of historical data from the Aquacheck proficiency testing scheme demonstrates improvement in the performance of participants correlated to the frequency of participation. Analysis of the spread of results returned by all participants, defined by the percentage relative standard deviation (RSD) and the performance (Z) scores awarded to the individual participants, indicates that the overall performance for the group of participants is consistent. However, when the frequency of participation is analysed, it can be clearly seen that those laboratories who participated in the majority of the distributions available reported 10–15% more acceptable (Z-scores between +2 and ?2) results than those labs who took part with a greatly reduced frequency. When ‘more difficult’ analytes are considered, those laboratories who participated in greater than 75% of available rounds reported up to 30% more acceptable results than those laboratories who participated in 25% or fewer, of the available rounds.