Performance of Canadian clinical laboratories processing throat culture proficiency testing surveys

Proficiency testing results obtained from simulated throat swab cultures sent between 1999 and 2013 were analyzed to evaluate the ability of participants to process, analyze, and properly report results for these cultures. Eight percent of all pathogen-positive samples were reported as false negatives, and 11 % of the pathogen-negative ones were reported as false positives. More than 90 % of the participants achieved acceptable grades in each of the proficiency testing samples containing Streptococcus pyogenes. Laboratories were less successful in reporting other significant pathogens including group C and G streptococcus and Arcanobacterium haemolyticum, although an overall increase in performance was observed for each subsequent survey. Most laboratories recognized other respiratory pathogens as not being agents of pharyngitis; a common issue with these specimens was the suggestion of the organism’s clinical significance when their presence was reported. The presence of small colony-forming β-hemolytic streptococcus (Streptococcus anginosus group) proved to be challenging for many laboratories as 66 % of all unacceptable grades for pathogen-negative throat swabs occurred in these PT samples. Moreover, performance in this group did not improve with subsequent surveys. Results obtained in this study support the added value of clinical relevancy challenges for proficiency testing as laboratories that may not have problems with the analytical aspect of the testing process struggle with the appropriate interpretation of results.     

A trial proficiency test of eight NAA laboratories in Asia using stream sediments

Eight neutron activation analysis research groups from seven countries have participated in a trial proficiency test under the auspices of the Forum for Nuclear Cooperation in Asia. Three stream sediment reference materials were used in the test. A high degree of proficiency was found in the quantification of Co and Sc and more than 20 elements were well quantified by the majority of laboratories. The results support the use of neutron activation analysis, as practised by the participants, for geochemical mapping. The data produced in this study may provide an opportunity to improve the characterisation of the three reference materials.     

Do accredited laboratories perform better in proficiency testing than non-accredited laboratories?

Accreditation and Quality Assurance - The CALA proficiency testing programme has been in operation since 1991. As CALA is also an accreditation body, every result reported as part of the CALA PT...     

Capability of laboratories to determine core nutrients in foods: results of an international proficiency test

A proficiency test (PT) to assess the capabilities of laboratories to determine nutrients in a biscuit sample was carried out in September 2009. The need for such interlaboratory comparison arose from an increasing nutrition labeling requirements of different countries around the world. Forty-eight laboratories worldwide participated in this PT program for the determination of total lipids, saturated fat, trans-fat, protein, sugars, total dietary fiber (TDF), ash and sodium in food. This program was organized under the auspices of the Asia-Pacific Laboratory Accreditation Cooperation (APLAC). APLAC considers PT programs as one of the objective means of assessing the performance of the accredited laboratories. The program is one of the APLAC PT series whose primary purposes are to establish mutual agreement on the equivalence of the operation of APLAC member laboratories and to provide an opportunity to identify testing deficiency so that corrective actions can be taken, if necessary. The results of this program indicated that the consensus mean values estimated by robust statistics were in good agreement with the corresponding values obtained in the homogeneity tests except for trans-fat and TDF. The relative standard deviations of participant results for trans-fat and TDF were also found to be higher (19 and 24%, respectively) than the other test parameters. The relative standard deviations for other test parameters were less than 10%. One-half of the laboratories obtained satisfactory z-scores (| z | < 3) (\left| z \right| < 3) for all their reported results. Although participants were instructed to provide the measurement uncertainties of their reported results, only 27.5% of them had done so. Albeit many of the measurement uncertainties appear to be reasonable, some of them were found to vary widely, indicating that some laboratories still have difficulties in estimating measurement uncertainties. Although the overall measurement capability can be considered to be satisfactory, there is still room for improvement of analytical procedures.     

How to interpret information from proficiency test exercises concerning the relative performance of accredited laboratories

If the results from various proficiency tests are used to compare the performance of accredited and non-accredited laboratories, great care must be taken not to come to contradicting conclusions when interpreting them. This paper intends to draw the attention to various aspects that should be taken into account when trying to make conclusions from the relative performance of accredited laboratories in proficiency testing.     

Organisation of proficiency schemes by testing and calibration laboratories

Accreditation and Quality Assurance - Each year, an increasing demand for proficiency testing is seen in the world. Participating in this type of activity has been adopted by testing and...     

Performance indication improvement for a proficiency testing

The paper discusses peculiarities of Z scores and E _n numbers, which are most often used for the treatment of proficiency test data. The important conditions of proper usage of these performance indicators and their improvement are suggested on the basis of systematic approach, on the idea of accuracy classification, and on some principles of optimality borrowed from information theory. The author believes that this paper may be of interest and practical value for all those engaged in applied metrology, specifically in the field of developing of and participating in proficiency testing programs, and in the activity connected with accrediting testing and calibration laboratories.Presented at 15th International Conference on Quality in Israel, November 2004     

First proficiency test for the determination of NORM in contaminated soil from the oil field

The Atomic Energy Commission of Syria (AECS), in cooperation with the Arabic Atomic Energy Agency (AAEA), has initiated the first proficiency test exercise for the determination of naturally occurring radioactive materials (NORM) in contaminated soil from the oil field. The soil sample was collected from one of the most highly radioactively contaminated lagoons with production water in the Syrian oil fields, which was then prepared, characterised and certified according to a standard procedure. Samples were dispatched to laboratories from eight Arab countries; Kuwait, Egypt, Yemen, Tunisia, Jordan, the Kingdom of Saudi Arabia, Libya and Syria. The results were evaluated using three statistical criteria; z-score, the U _test score and the relative bias. These statistical methods were used to evaluate the performance of each laboratory, in addition to the overall evaluation for each radionuclide. This evaluation has indicated that 57% and 86% of the results passed the criteria set for precision and accuracy applied for this test in relation to ²²⁶Ra and ²²⁸Ra, respectively. These two radionuclides are considered to be the most important radionuclides in the oil industry.     

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.     

Performance of uncertainty evaluation strategies in a food proficiency scheme

A study of the performance of different uncertainty evaluation strategies among 163 voluntary respondents from food proficiency schemes is presented. Strategies included use of: single-laboratory validation data, quality control data, past proficiency testing data, reproducibility data, a measurement equation and the dispersion of replicate observations on the test material. Most performed reasonably well, but the dispersion of replicate observations underestimated uncertainty by a factor of approximately 3. Intended compliance with accreditation requirements was associated with significantly improved uncertainty evaluation performance, while intended compliance with the ISO “Guide to the expression of uncertainty in measurement” had no significant effect. Substituting estimates based on the Horwitz or Horwitz–Thompson models or on PT target standard deviation for the respondents’ own estimates of uncertainty led to a marked reduction in poor zeta scores and significant improvement in dispersion of zeta scores.     

The relationship between accreditation status and performance in a proficiency test

In the FAPAS proficiency testing scheme, participants are asked to state whether the analytical method used was accredited or not accredited. It is thus possible to compare the stated accreditation status with performance in the scheme. For this purpose, fifty qualifying examples of analyte-test material combination were selected at random from the reports from the year 2006. The accredited/non-accredited subsets of results from each example were subjected to a statistical analysis to determine whether any significant differences between the distributions of results could be detected. Outliers were removed from the datasets before the main statistical tests and considered separately. The inlying data were subjected to non-parametric tests for differences in central tendency and dispersion. A few significant examples were found, but could be reasonably attributed to chance. Among the inliers there were no grounds to reject the overall null hypothesis, that is, that accreditation has no effect on performance. However, the proportion of outliers was about twice as high among the non-accredited group.     

Impact of international standards and initiatives on proficiency testing for medical laboratories

This paper is intended to briefly discuss several recent initiatives regarding External Quality Assessment (or Proficiency Testing) (PT/EQA) for medical laboratories in various parts of the world. While a brief paper cannot be comprehensive for all regions, it is possible to present some new standards and initiatives that are underway or proposed in many countries. Laboratory medicine was one of the first areas of laboratory testing to develop interlaboratory comparisons, and the first area where such comparisons became compulsory. Because of that, the medical field has often been the leader in the availability and use of PT/EQA, and has introduced many innovations that have been adopted in other areas. Perhaps other areas of testing will similarly adopt the developments discussed here, if they have not already done so. There are important developments in the medical area that are also occurring in other fields of testing, such as the growing number of countries that require some form of participation, and the increasing use of the Internet. These developments are important, but are not discussed further in this paper since they are occurring in many fields of testing.     

Impact of international standards and initiatives on proficiency testing for medical laboratories

This paper is intended to briefly discuss several recent initiatives regarding External Quality Assessment (or Proficiency Testing) (PT/EQA) for medical laboratories in various parts of the world. While a brief paper cannot be comprehensive for all regions, it is possible to present some new standards and initiatives that are underway or proposed in many countries. Laboratory medicine was one of the first areas of laboratory testing to develop interlaboratory comparisons, and the first area where such comparisons became compulsory. Because of that, the medical field has often been the leader in the availability and use of PT/EQA, and has introduced many innovations that have been adopted in other areas. Perhaps other areas of testing will similarly adopt the developments discussed here, if they have not already done so. There are important developments in the medical area that are also occurring in other fields of testing, such as the growing number of countries that require some form of participation, and the increasing use of the Internet. These developments are important, but are not discussed further in this paper since they are occurring in many fields of testing.

     

A model to set measurement quality objectives and to establish measurement uncertainty expectations in analytical chemistry laboratories using ASTM proficiency test data

A model is presented that correlates historical proficiency test data as the log of interlaboratory standard deviations versus the log of analyte concentrations, independent of analyte (measurand) or matrix. Analytical chemistry laboratories can use this model to set their internal measurement quality objectives and to apply the uncertainty budget process to assign the maximum allowable variation in each major step in their bias-free measurement systems. Laboratories that are compliant with this model are able to pass future proficiency tests and demonstrate competence to laboratory clients and ISO 17025 accreditation bodies. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/ 10.1007/s007690100398-y. Received: 31 March 2001 Accepted: 11 September 2001     

Visualisation of proficiency test exercise results in Kiri plots

A novel graphical method (‘Kiri plots’) for the presentation of proficiency test exercise results is presented. The Kiri plot visualises the evaluation of the proficiency test results based on three statistical tests (the z score, the zeta score and the relative uncertainty outlier test) by defining six zones including a central “in agreement” zone.     

Evaluation of the performance of 57 Japanese participating laboratories by two types of z-scores in proficiency test for the quantification of pesticide residues in brown rice

A proficiency test for the analysis of pesticide residues in brown rice was carried out to support upgrading in analytical skills of participant laboratories. Brown rice containing three target pesticides (etofenprox, fenitrothion, and isoprothiolane) was used as the test samples. The test samples were distributed to the 57 participants and analyzed by appropriate analytical methods chosen by each participant. It was shown that there was no significant difference among the reported values obtained by different types of analytical method. The analytical results obtained by National Metrology Institute of Japan (NMIJ) were 3 % to 10 % greater than those obtained by participants. The results reported by the participant were evaluated by using two types of z-scores, that is, one was the score based on the consensus values calculated from the analytical results of participants, and the other one was the score based on the reference values obtained by NMIJ with high reliability. Acceptable z-scores based on the consensus values and NMIJ reference values were achieved by 87 % to 89 % and 79 % to 94 % of the participants, respectively. Graphical Abstract

Distribution of z and z_NMIJ-scores for isoprothiolane