Interlaboratory Proficiency Testing Research Articles

Proficiency testing for bacterial whole genome sequencing: an end-user survey of current capabilities, requirements and priorities

The advent of next-generation sequencing (NGS) has revolutionised public health microbiology. Given the potential impact of NGS, it is paramount to ensure standardisation of ‘wet’ laboratory and bioinformatic protocols and promote comparability of methods employed by different laboratories and their outputs. Therefore, one of the ambitious goals of the Global Microbial Identifier (GMI) initiative (http://www.globalmicrobialidentifier.org/) has been to establish a mechanism for inter-laboratory NGS proficiency testing (PT). This report presents findings from the survey recently conducted by Working Group 4 among GMI members in order to ascertain NGS end-use requirements and attitudes towards NGS PT. The survey identified the high professional diversity of laboratories engaged in NGS-based public health projects and the wide range of capabilities within institutions, at a notable range of costs. The priority pathogens reported by respondents reflected the key drivers for NGS use (high burden disease and ‘high profile’ pathogens). The performance of and participation in PT was perceived as important by most respondents. The wide range of sequencing and bioinformatics practices reported by end-users highlights the importance of standardisation and harmonisation of NGS in public health and underpins the use of PT as a means to assuring quality. The findings of this survey will guide the design of the GMI PT program in relation to the spectrum of pathogens included, testing frequency and volume as well as technical requirements. The PT program for external quality assurance will evolve and inform the introduction of NGS into clinical and public health microbiology practice in the post-genomic era.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-015-0902-3) contains supplementary material, which is available to authorized users.

Participation of Accredited Laboratories in Proficiency Testing Schemes and Interlaboratory Comparisons

This paper presents the elements of metrology laboratory accreditation for calibration in the scope of calibration E-05 Dimensions, and calibration for the subject: the distance and angle measures. During the accreditation, but also in its maintenance, calibration laboratories must prove their competence. Each laboratory must have the quality management procedures for monitoring the validity of the calibrations performed. This monitoring shall be planned and reviewed through: internal quality control, participation in the interlaboratory comparisons or proficiency testing schemes, repeated calibrations using the same or different methods, re-calibration of the saved samples and correlation of results for different characteristics of the sample. According to the ISO/IEC 17025:2005 standard, competence is proved by participating in interlaboratory comparisons or participation in Proficiency testing (PT) schemes. This paper aims to stimulate discussion and debate about ways of proving competence of calibration laboratories. We believe that, in the interpretation of ISO/IEC 17025, the laboratory can demonstrate competence by participating in any activity, PT schemes or interlaboratory comparisons, and they are equal to this need. The procedure and the results of the interlaboratory comparisons between two accredited laboratories will be described.

Accreditation of the analytical method used for nitrate determination in vegetables

The standard method of EN 12014-7 was used for the determination of nitrate content in vegetables in the Central Laboratory of the Agricultural Institute of Slovenia. Trueness of the method was verified by the analysis of samples in the interlaboratory proficiency testing scheme Bipea (Bureau Interprofessionnel d'Etudes Analytiques). Linearity was confirmed by multiple linear regression; the correlation coefficient (R2) was 0.9993. The limit of detection (LOD) was calculated as 0.8 mg NO3-/kg and limit of quantification (LOQ) 3.0 mg NO3-/kg. Relative standard deviation (RSD) of repeatability was 4.6% and RSD of reproducibility 8.9%. The relative uncertainty of repeatability and reproducibility were 10.5% and 20.2%, respectively. The method has been accredited by the French Accreditation Committee COFRAC in 2007 and by the national Slovene Accreditation in 2012.

Determination of the Concentration of Carbonic Species in Natural Waters: Results from a World‐Wide Proficiency Test

The results of an international interlaboratory proficiency test for the determination of carbonic species are presented. Eight laboratories analysed twelve water samples (four synthetic waters, one lake water, four geothermal waters, one seawater and two petroleum waters) by two methods: (a) individual laboratory analytical procedure and (b) acid–base titration curves in tabular form following a standardised protocol. In case (b), the concentrations of carbonic species were calculated by the organiser using the (1) Hydrologists' method, (2) Geochemists' method and/or (3) initial pH and total alkalinity method. For synthetic waters, the averaged % trueness and precision of measurement of the two methods were (trueness = 7.6, precision = 9.4) and (9.0, 3.4) for total alkalinity, and (6.6, 31.0) and (7.8, 6.1) for carbonic alkalinity, respectively. This indicates that the total alkalinity calculation procedure is in general correct in the individual laboratory method, but the carbonic alkalinity calculation procedure has serious problems. The measurements of total alkalinity for lake and seawaters were in agreement in both the methods; however, the individual laboratory measurement method for geothermal and petroleum waters was conceptually incorrect. Thus, the analytical procedures for the determination of carbonic species were reviewed. To apply the Hydrologists' and/or Geochemists' methods, the location of NaHCO3EP and H2CO3EP is necessary, even for samples with pH lower than that of NaHCO3EP, and a backward titration curve after complete removal of CO2 must be performed. The initial pH and total alkalinity method is appropriate where a complete analysis of species that contribute to the alkalinity is known.

Five year results of an international proficiency testing programme for measurement of antifungal drug concentrations

Since 2007 the Dutch Association for Quality Assessment in Therapeutic Drug Monitoring (KKGT) has organized an international interlaboratory proficiency testing (PT) programme for measurement of antifungal drugs in plasma. We describe the 5 year results of the laboratories' performance. Twice a year, laboratories received a set of blind plasma samples containing low or high concentrations of fluconazole, itraconazole, hydroxyitraconazole, posaconazole, voriconazole and flucytosine. Participating laboratories were asked to report their results within 6 weeks after dispatch and provide details of their analytical methods. Results deviating >20% from the weighed-in concentration were considered inaccurate. Four-way ANOVA was performed to assess the effect of antifungal drug measured, concentration, analytical method and performing laboratory on the absolute inaccuracy. In 2012, a questionnaire based on the CLSI guidelines was dispatched with the request to provide input on sources of error. Fifty-seven laboratories (13 countries) reported 2251 results (287 fluconazole, 451 itraconazole, 348 hydroxyitraconazole, 402 posaconazole, 652 voriconazole and 111 flucytosine) in 5 years. Analyses were performed using HPLC (55.0%), LC-MS(/MS) (43.4%), UPLC (1.4%) or GC-MS (0.2%). Overall, 432 (19.2%) analyses were inaccurate. The performing laboratory was the only factor clearly associated with inaccuracies. The questionnaire results indicated that laboratories encounter significant problems analysing low concentrations (15.4% of all inaccuracies). Results of the PT programme suggest that one out of five measurements is inaccurate. The performing laboratory is the main determinant of inaccuracy, suggesting that internal quality assurance is pivotal in preventing inaccuracies, irrespective of the antifungal drug measured, concentration and analytical equipment.

Interlaboratory Reproducibility and Proficiency Testing within the Human Papillomavirus Cervical Cancer Screening Program in Catalonia, Spain

In Catalonia, a screening protocol for cervical cancer, including human papillomavirus (HPV) DNA testing using the Digene Hybrid Capture 2 (HC2) assay, was implemented in 2006. In order to monitor interlaboratory reproducibility, a proficiency testing (PT) survey of the HPV samples was launched in 2008. The aim of this study was to explore the repeatability of the HC2 assay's performance. Participating laboratories provided 20 samples annually, 5 randomly chosen samples from each of the following relative light unit (RLU) intervals: <0.5, 0.5 to 0.99, 1 to 9.99, and ≥10. Kappa statistics were used to determine the agreement levels between the original and the PT readings. The nature and origin of the discrepant results were calculated by bootstrapping. A total of 946 specimens were retested. The kappa values were 0.91 for positive/negative categorical classification and 0.79 for the four RLU intervals studied. Sample retesting yielded systematically lower RLU values than the original test (P<0.005), independently of the time elapsed between the two determinations (median, 53 days), possibly due to freeze-thaw cycles. The probability for a sample to show clinically discrepant results upon retesting was a function of the RLU value; samples with RLU values in the 0.5 to 5 interval showed 10.80% probability to yield discrepant results (95% confidence interval [CI], 7.86 to 14.33) compared to 0.85% probability for samples outside this interval (95% CI, 0.17 to 1.69). Globally, the HC2 assay shows high interlaboratory concordance. We have identified differential confidence thresholds and suggested the guidelines for interlaboratory PT in the future, as analytical quality assessment of HPV DNA detection remains a central component of the screening program for cervical cancer prevention.

Measurements of gamma (γ)-emitting radionuclides with a high-purity germanium detector: the methods and reliability of our environmental assessments on the Fukushima 1 Nuclear Power Plant accident

The severe accident of Fukushima 1 Nuclear Power Plant due to the Tohoku Region Pacific Coast Earthquake in 11 March 2011 caused wide contamination and pollution by radionuclides in Fukushima and surrounding prefectures. In the current JPR symposium, a group of plant scientists attempted to examine the impact of the radioactive contamination on wild and cultivated plants. Measurements of gamma (γ) radiation from radionuclides in "Fukushima samples", which we called and collected from natural and agricultural areas in Fukushima prefecture were mostly done with a high-purity Ge detector in the Graduate School of Maritime Sciences, Kobe University. In this technical note, we describe the methods of sample preparation and measurements of radioactivity of the samples and discuss the reliability of our data in regards to the International Atomic Energy Agency (IAEA) Interlaboratory comparisons and proficiency test (IAEA proficiency test).

Determination of Ochratoxin A in Food by High Performance Liquid Chromatography

Ochratoxin A (OTA) is an important mycotoxin that is produced by Aspergillus and Penicillium species. Ochratoxin A is a common contaminant of various foods including cereals, spices, coffee, cacao, beer, wine, raisins, pulses, meat, meat products, or edible offal. Due to a wide range of its toxic effects in humans and animals, ochratoxin A needs to be monitored. With regard to this necessity, a sensitive HPLC-FD method for purposes of the quantification of trace amounts of ochratoxin A in foods of plant and animal origin was developed, validated and applied for analysis. Food samples were cleaned using commercial immunoaffinity columns and analyzed by means of a high performance liquid chromatography method with fluorescence detection. Limit of quantification of the method ranged between 0.01–0.30 µg/kg depending on the sample matrix. Recoveries were 80–88% in the concentration range of 0.01–0.30 µg/kg, depending upon sample type. The quality of laboratory results was confirmed by successful participation in international inter-laboratory proficiency testing. This laboratory was accredited accordance to CSN ISO/EN 17025. The developed method was applied to the determination of ochratoxin A in samples from 61 types of foodstuffs of plant and animal origin, that were collected in 4 sampling terms at 12 regions of the Czech Republic in years 2011–2012. In total, 732 food samples were gathered and analyzed.

Interlaboratory comparison for determination of ochratoxin A by ELISA in maize (running title: Determination of ochratoxin A in maize)

Participation in interlaboratory comparison and proficiency testing schemes is important for laboratories to control the work quality. In this study, a sample of naturally contaminated maize was analyzed for the content of ochratoxin A (OTA) in three laboratories in Serbia. Participating laboratories used enzymatic immunoaffinity method (ELISA) for the determination of OTA and selection of the ELISA kit was free. Between-laboratory precision was acceptable as evidenced by Cochran?s C test. Moreover, z-scores for all three laboratories were z &lt; ? 2, which is considered acceptable. Used OTA confirmation methods were thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC), with fluorescence detector. The results of different methods were comparable.

Determination of trans,trans‐muconic acid in workers' urine through ultra‐performance liquid chromatography coupled to tandem mass spectrometry

A novel method for the biological monitoring of benzene-exposed workers has been developed through ultra-performance liquid chromatography coupled to tandem mass spectrometry. The method uses trans,trans-muconic acid in urine as the benzene-exposure biomarker. The method was developed using a triple quadrupole mass spectrometer with enough sensitivity to facilitate diluting and injecting the urine samples directly, rather than performing a solid-phase extraction procedure as is common in the available protocols. Moreover, compared with a conventional high-pressure liquid chromatography system, the separation power provided by the ultra-performance liquid chromatography system allows a 10-fold reduction in run time. The method was adjusted to a dynamic range of between 198.9 and 4916.7 µg/L to cover the biological exposure index of trans,trans-muconic acid in urine. Also, the method demonstrated intra-day and inter-day precision at 98%, and accuracy within an acceptable range of 101 ± 8%. The method has been used to quantify various types of urine samples, such as workers' urine and inter-laboratory proficiency tests. Depending on the sample, the quantified levels ranged from less than the limit of quantitation to 3836.7 µg/L. No levels exceeding the calibration range were detected in the urine of workers, and the reported concentrations in urine for the proficiency tests were, as expected, based on known values. Moreover, the new method using sample dilution and faster chromatographic run was more effective, facilitating fast communication of results, as needed, to decision-makers.

Determination of Na, K, Mg and Ca in biodiesel by LS F AAS and HR-CS F AAS: studies that supported the proposal of the ABNT NBR 15556 norm

Recently, ABNT (Brazilian Association of Technical Standards) has presented a set of norms related to the determination of Na, K, Mg and Ca in biodiesel, recommending procedures similar to those of the European and American norms. However, it has also introduced an alternative norm (ABNT NBR 15556) wherein these 4 elements can be determined by flame atomic absorption spectrometry (F AAS). This work presents the studies that have supported this proposal and compares the performance of linear source equipment with a continuous source one in the application of the norm. Among the optimized factors, the low aspiration rate and the use of mineral oil solution in xylene to adjust the viscosity between samples and calibration solutions are highlighted. Precision tests (repeatability and intermediary precision) have shown adequate values, confirming the robustness of the method. Limits of detection were suitably below the legislation limits. The accuracy was confirmed by recovery tests as well as by the participation in interlaboratory proficiency tests promoted by the National Agency on Oil, Natural Gas and Biofuels (ANP, Brazil). The determination of these 4 elements by F AAS brings evident economic advantages to the producer, once F AAS is less expensive to purchase and maintenance.

Application of the redox potential measurementbased rapid method in the microbial hygienic control

The standard culture methods in food hygiene used for the determination of microbial count are slow. In order to shorten the duration of detection of sampled bacteria, the Authors elaborated a redox potential measurement-based new method. The applicability of the new method was compared to the standard swab method in the framework of interlaboratory proficiency test aimed to determine the microbial contamination of model surfaces and in the hygienic control of a food manufacturing pilot plant. The comparative evaluation of total counts and Enterobacterium counts obtained by standard plate pouring and by the new method proved that there is no significant difference between the results of the two procedures. The total count determination with the new method lasted only 10–16 h in contrast to 72 h of plate counting. Particular advantages of the new method are that the bacterial count of the swab can be determined directly, without any washing down of the microbes from the swab and due to the different shapes...

Using Interlaboratory Proficiency Data to Guide NIR/MIR Calibrations

There is growing interest in the use of near-range and/or midrange infrared (IR) diffuse reflectance spectroscopy (NIR and MIR) as nondestructive alternatives to chemical testing of soils. This trend is supported by research on how best to correlate IR spectral data with results obtained by conventional laboratory measurements. While for soils there is growing interest in developing local and national calibrations using “legacy” data, the proven analytical performance of provider laboratories now and earlier, the moisture status of reported results, and the method of soil preparation warrant greater attention. Examples for soil carbon (C) and total soil nitrogen (N) from Australasian interlaboratory proficiency testing across multiple years from 1993 are provided to demonstrate the magnitude of past and present measurement uncertainties, including the effects of method and different concentrations. The evidence is sufficient to require those commissioned to develop NIR and MIR calibrations to subject their prototype calibrations to external peer review by participating in credible, independent interlaboratory proficiency testing programs for ≥12 months, including checks on soil moisture status and possible effects of sample preparation. To rate as credible for most uses, the prototype results should be within the interquartile range for each sample and ideally there should be no outliers and few stragglers. Across the period of assessment (1993–2008), users of Walkley and Black organic C and Kjeldahl digestion for total soil N (Kjeldahl method does not measure total N, but most of the organic N plus an undetermined proportion of nitrate and nitrate present in the sample; quantitative inclusion of both requires a modification of the Kjeldahl procedure) declined as use of furnace technologies for soil C and N increased linearly. There is a strong case to commission two or three well-performing and experienced laboratories to reanalyze samples in “legacy” soil collections prior to finalizing predictive relationships with NIR/MIR spectra for the same samples.

Inter-laboratory test on drug residues in water intended for human consumption

In June 2009, the Laboratory in hydrology of Nancy (Ansès-LHN, Nancy) conducted an exploratory inter-laboratory proficiency tests (ILT) test in collaboration with the AQUAREF network to identify laboratory practices and estimate inter-laboratory uncertainty for the compounds under study. There were a total of 12 compounds belonging to six families (hormones, antibiotics, non-steroidal anti-inflammatory drugs, beta blockers, antipsychotics and others) including one compound used in veterinary medicine. It was the first ILT conducted in France on water intended for human consumption. Thirty-one laboratories participated, 4 of which were located abroad.

New, Comprehensive Soil Chemical Methods Book for Australasia

The 1992 Australian Laboratory Handbook of Soil and Water Chemical Methods (the handbook) of Rayment and Higginson defines much of the contemporary soil chemical methodology used in Australia for soil fertility and land-resource survey assessments. In addition, codes from the handbook identify methodological details in Australian soil databases, while the codes summarize most tests used for certification purposes by the Australasian Soil and Plant Analysis Council (ASPAC) in its interlaboratory soil proficiency testing programs. A worthy, comprehensive replacement was required as the handbook is out of date in places and out of print. This article provides information on the handbook's replacement with a new book by Rayment and Lyons, titled Soil Chemical Methods-Australasia. Method codes and other strengths of the handbook have been retained and many new tests have been added. There are new chapters on acid sulfate soils, total miscellaneous elements, and miscellaneous extractable elements, plus inclusions and improvements throughout. Modern analytical techniques, such as flow-injection analysis, inductively coupled plasma–mass spectroscopy (ICP-MS), and potential alternatives to chemical testing offered by near-range and midrange infrared diffuse reflectance spectroscopy, are included. Examples of new additions include the Mehlich 3 “universal” soil test (and derived environmental P tests) and methods for potentially mineralizable nitrogen, labile carbon, particulate organic carbon, and charcoal. Around 200 methods are fully described, while information of measurement performance at different concentrations is provided where credible data were available from multiple, interlaboratory proficiency programs of ASPAC. Procedures for the chemical testing of water are no longer included, except where relevant to saturation extracts of soils. While there are informative and much expanded method preambles and reference lists, the new 2011 book has its focus on methodology. A scheme to agree on recommended methods for different soils and regional locations is outlined.

Interlaboratory proficiency testing of tensile and flexural testing for cellulose based transformed board material

Optimum safety and reliability can be achieved by coordinating an interlaboratory proficiency testing among different laboratories. Testing laboratories need to verify their test procedures and testing capability for reliable results. In this study, equivalent samples are prepared by cellulose based transformed board material used in transformers as electrical isolation material. Randomly selected test samples having specified dimensions are sent to the participant laboratories. Then they are tested and results are analyzed according to previously defined parameters. Each laboratory applied tensile and flexural tests on the samples according to procedures given in IEC 60641-2, 2004 and IEC 60763-2, 2007 standards respectively. Test results are evaluated according to same procedures explained in related standards by the participant laboratories. TUBITAK UME Material Testing Laboratory being the pilot laboratory collected to the all evaluated results including associated measurement uncertainties. Then the collected results evaluated according to ISO 17043, 2010 are reported by each laboratory as a part of the proficiency test report. Z-scores of the participant laboratories are presented.

Rapid quantification of ionophores in feeds by liquid chromatography– tandem mass spectrometry

Ionophores are widely used in veterinary medicine as coccidiostats and for improving nutrient utilization in livestock production. Because of widespread use, ionophores sometimes cause poisoning in livestock. Quantifying concentration of these compounds in feeds for diagnostic purposes is needed. A method with a single step of solvent extraction was developed for rapid simultaneous quantification of monensin, lasalocid, salinomycin, and narasin in feeds by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The ionophores were extracted using methanol:water (90:10). With the high specificity and high sensitivity of tandem mass spectrometry, the extract was introduced for measurement without further processing. The effect of particle size of feeds on extraction efficiency was also investigated. It was found that feeds passing through a 1-mm filter or sieve show better quantitative extraction. Nigericin was used as internal standard for the measurement. The method was validated by fortification of the selected ionophore compounds in horse feed at different concentrations. The typical recovery rate was 69-122%. Meanwhile, various interlaboratory proficiency test samples of different matrices were also quantified as part of the procedure for method validation. A good agreement was found between results and the suggested values. The method is very sensitive, with detection limits between 0.018 µg/g and 0.056 µg/g for the compounds tested. Results showed that the lower limit of quantification was 0.2 µg/g for the ionophore compounds, which is much lower than the contents of the ionophores in medicated feeds, which is generally approximately 10-100 µg/g feed.

Interlaboratory proficiency testing: Intercomparison in relation to the measurement of alumina, iron(III) oxide and Titania present in homogenised china clay

For establishing technical competence in testing and calibration, a laboratory has to participate in proficiency testing (PT) program from time to time. An intercomparison in the field of chemical analysis using classical and instrumental methods of analysis has been carried out by 17 accredited as well as non accredited laboratories in India as per requirement of National Accreditation Board for Testing and Calibration Laboratories(NABL), New Delhi. Central Glass and Ceramic Research Institute(CGCRI), Kolkata acted as a nodal laboratory and conducted this PT programme during 2000–2001. This paper reports the analytical results and statistical evaluation of the results using Z-score.

Evaluation of the TEST 1 erythrocyte sedimentation rate system and intra- and inter-laboratory quality control using new latex control materials

The erythrocyte sedimentation rate (ESR) test has been considered to be a simple procedure, not requiring quality control (QC). However, QC is essential for accuracy and precision. We evaluated the TEST 1 ESR system and performed QC procedures using newly developed latex control materials in three hospitals. Using tripotassium ethylenediaminetetraacetic acid blood samples (n=184), we compared TEST 1 ESR values with Westergren ESR data and evaluated intra-assay precision. Three levels of latex control materials were used to assess inter-assay precision. Reference range assessment was done using samples from 220 healthy individuals. Inter-laboratory QC with latex control materials in three hospitals was performed. Correlation between TEST 1 ESR and Westergren ESR results was good (p<0.001). Intra-assay precision [coefficients of variation (CV) 6.6%-21.7%] with patient samples and inter-assay precision (CV 0.0%-6.8%) with latex control materials were satisfactory. The reference ranges of 2-10 mm/h for males and 2-19 mm/h for females were established. Inter-laboratory QC data with latex control materials in three hospitals demonstrated good accuracy and satisfactory precision (CV 0.0%-14.4%). Our results demonstrate that the TEST 1 QC is reliable and the latex control materials are valuable for inter-laboratory proficiency testing.

Evaluation of testing capabilities for the determination of melamine in milk through an interlaboratory proficiency test programme during the melamine crisis

An interlaboratory proficiency testing programme for melamine in milk was organized for field laboratories in Hong Kong, China, during the melamine crisis in late September 2008. One blank test sample and three homogenous samples prepared by gravimetric spiking of melamine at the concentration range of zero to 4.5 mg kg−1 were given to participants in this programme. A total of 13 participants returned the results to the organizer and they used either liquid chromatography-tandem mass spectrometry (LC-MS/MS) or gas chromatography-mass spectrometry (GC-MS) for their determinations. The performance of the participants was assessed by determining z-scores, calculated from the bias from the assigned reference values and Horwitz standard deviation. The median values of pooled data were found to be in good agreement with the reference values and the majority of the participants demonstrated their capabilities in the quantitative measurement of melamine in milk samples. However, four participants gave false-positive results for the blank test sample, probably due to cross-contamination from other samples, and they were requested to investigate the actual causes. In summary, eight participants (or 62%) demonstrated their competence for all the four test samples.