ĐÁNH GIÁ TÍNH ĐỒNG NHẤT VÀ ĐỘ ỔN ĐỊNH MẪU HBV DNA ĐÔNG KHÔ THEO TIÊU CHUẨN VỀ MẪU NGOẠI KIỂM

Mục tiêu: Xây dựng quy trình sản xuất mẫu HBV DNA đông khô sử dụng trong ngoại kiểm. Đánh giá tính đồng nhất và độ ổn định của mẫu huyết tương HBV DNA đông khô sau sản xuất. Phương pháp nghiên cứu: Nghiên cứu thực nghiệm trên các mẫu huyết tương dương tính HBV DNA, đánh giá tính đồng nhất và độ ổn định của mẫu huyết tương HBV DNA đông khô bằng kiểm định so sánh một trung bình (Oneway ANOVA) và phép kiểm T- test. Kết quả: Mẫu huyết tương HBV DNA đông khô với 3 mức nồng độ đạt tính đồng nhất, độ ổn định vận chuyển trong 7 ngày. Mẫu đạt độ ổn định bảo quản tại nhiệt độ -20°C lên đến 150 ngày, ở nhiệt độ 2-8°C trong 90 ngày, ở nhiệt độ 25°C và 37°C trong 10 ngày (giá trị p > 0.05). Kết luận: Quy trình sản xuất mẫu HBV DNA đông khô đã được xây dựng thành công. Tính đồng nhất và độ ổn định của các mẫu được sản xuất đáp ứng các tiêu chí của tiêu chuẩn ISO 13528:2015 và ISO guide 35.

Bovine Serum as an Alternative to Control Serum for Total Protein Levels

Total protein describes the liver's ability to synthesize proteins and metabolize substances in the blood. Bovine serum can be used as a control material because the total protein analyte in bovine blood serum is almost identical to the analyte in human serum. The researchers intend to determine the homogeneity and stability of bovine serum with the addition of 7,5% ethylene glycol preservative after being stored for 12 weeks at -20°C as an alternative to control serum for total protein levels. This research used survey analytics using a one-group pretest-posttest research design. Data analysis used ISO 13528 2005 calculations. From the examination of the total protein level in the serum, the value of Xr – Yr = 0.23817, which is where the value meets the test criteria according to | Xr - Yr | <0.36, that is 0.23817 <0.91585. The total protein content of bovine serum was homogeneous and stable with the addition of 7.5% ethylene glycol stored at -20oC for 12 weeks.

Introduction to Statistical Methods for Outlier Detection and Sample Homogeneity Assessment of Reference Materials and Proficiency Test Items

Due to the homogeneity of the product or sample, it will affect whether it meets the scope of application and purpose. For example, the reference materials(RM) produced by the reference material producer(RMP), and the proficiency test items selected by the proficiency testing provider(PTP), in order to ensure the reference materials or proficiency test items have consistent characteristics or comparability, they should be proved to have certain homogeneity. However, before performing homogeneity assessment, it is necessary to measure the characteristic parameters of the reference materials or proficiency test items to obtain a sufficient number of measured values for data analysis, but there may be outliers in the measured values that may affect data analysis and interpretation of the results. Therefore, this article will refer to ASTM E178-16a:2016[1], ISO 5725-2:1994[2], ISO 13528:2015[3], etc., to introduce several outlier detection and homogeneity assessment methods, supplemented by case studies. Finally, this article will remind the precautions for the use of the method, so that readers can choose the appropriate method for use in the actual analysis.

Organisation of Multi-Mycotoxin Proficiency Tests: Evaluation of the Performances of the Laboratories Using the Triple A Rating Approach

In accordance with the International Standard Organization ISO 17043, two proficiency tests (PTs) for the simultaneous determination of aflatoxins (AFB1, AFB2, AFG1, AFG2); deoxynivalenol; fumonisins FB1, FB2, and B3; ochratoxin A, the T-2 toxin; and the HT-2 toxin were conducted in 2019 and 2020 using cornflakes and rusk flours that were prepared in house. The homogeneity and the stability of these materials were verified according to the criteria laid down in ISO 13528 using randomly selected samples. Most of the targeted toxins were found to be homogenously distributed in both materials with no significant changes during the timescale of the PTs. Next, the materials were distributed to approximately 25 participating laboratories from Europe, Canada, and the United States. The obtained datasets were computed using robust statistics. The outliers were checked and removed, and the toxin concentrations were assigned as the consensus value of the results of the participants at Horwitz ratios <1.2. The z scores were generated for all mycotoxins, and the results were pooled to calculate the relative sum of squared z scores (SZ2) indexes and were clustered according to the triple A rating. Overall, at least 80% of the participating laboratories achieved good and acceptable performances. The most frequent categories assigned to good performances (SZ2 ≤ 2) were AAA (51%) and BAA (13%). Clusters of BBA + CBA (6%) included laboratories reporting acceptable z scores <90% of the total z scores for less than 90% or 50% of the mycotoxins targeted in the 2 matrices. The triple A rating seems to be appropriate in evaluating the performances of laboratories involved in multi-mycotoxin analyses. Accredited and non-accredited analytical methods achieved good and acceptable performances.

Production and application of lyophilized urine samples used in microbiology external quality assessment programme in Vietnam

Introduction: The external quality assessment (EQA) for microbiological laboratories is one of the most commonly used services for quality assurance. In Vietnam, the majority of EQA samples are imported from foreign markets, involving high costs, complicated procedures and further making it difficult to ensure quality in terms of transport and management. The objective of this study was to develop a process for producing lyophilized urine samples containing pathogens (Escherichia coli and Enterococcus faecalis), evaluating the homogeneity and stability of the produced samples and the subsequent application of these samples in the launching trial program of the clinical microbiology program. Methods: The production process of was established according to ISO Guide 34:2009. The homogeneity and stability of production samples were evaluated according to the guidance of ISO 13528:2015. Produced samples were preserved at 2-8°C and assessed for stability after 2, 4, 6, 8, 10, and 12 weeks. Samples were subsequently utilized in the clinical microbiology EQA program, wherein they were sent to 26 laboratories located in several different regions across Vietnam. Results: The production process thus conceived comprised eight steps that ensured the homogeneity of the samples produced. Two sets of quality samples were produced and stability within12 weeks. Approximately 92% of the laboratories met the set target. Conclusions: The eight-step process to produce presumptive lyophilized urine samples has successfully developed. The produced samples reach the criteria for EQA samples and suitable to apply on clinical microbiology EQA scheme at national scale.

UNIFORMITY OF RESULTS OF MULTIPLE MEASUREMENT SERIES DURING PREPARING A CONTROL SAMPLE FOR QUALIFICATION TESTS

The work examines the methodology for assessing the homogeneity of the control sample of interlaboratory qualification tests, which is the most important characteristic of determining its status. The criterion for assessing the homogeneity between the characterizing values of the samples is the root mean square deviation and standard deviation of the proficiency test of the control sample with the standard uncertainty of the assigned value, which is a requirement of the ISO 13528 standard. Ignoring this requirement may provoke a false assessment of the participated laboratories taking corrective action.

Iterative Cochran’s C test as a multivariate method to detect higher than expected variability: a microbiological inter-laboratory ring trial as a case-study

IntroductionAn interlaboratory calibration analysis was carried out to validate a methodology for a European standard for domestic laundry disinfection, using different doses of disinfectant and microorganisms. ISO 5725-2 and ISO 13528 form the basis of interlaboratory validations of quantitative methods, but there is a need for a simple graphical method to detect differences in laboratory behavior in terms of accuracy and variability.ObjectiveA novel multivariate method based on the classical Cochran’s C test, as well as PCA and bootstrapping, which allows the inclusion of different correlated variables, was applied to identify higher variability than expected in factor (e.g. laboratories) levels, and the detection of multivariate outliers in a reduced space.MethodsThe proposed method is based on resampling, using the same sample many times but removing cases at random and performing Cochran’s C test for all the variables together in a reduced space.ResultsThe method was tested by checking 7 laboratories for high variability in different parameters (logarithmic reduction (LR), cross contamination (RI), and wash water (WW)). After applying the proposed statistical analyses, no reasons were found to reject any of the participating laboratories. Multiple applications of the method are possible and we describe a case study in which the multivariant iterative Cochran’s C test was used: variability detection with multiple microbiological parameters (with high variability) during an interlaboratory ring trial.

Bivariate confidence probability plots as a method to test the accuracy and variability of microbiological measures

IntroductionIn an interlaboratory calibration analysis to validate a methodology that will be proposed as a European standard for domestic laundry disinfection, tests were carried out to detect if there are different behaviors in the measurements regarding accuracies and variabilities. Interlaboratory tests using different doses of disinfectant and microorganisms were carried out. ISO 5725-2 and ISO 13528 form the basis of validations of quantitative methods, providing validation specifications for interlaboratory studies. However, a need for a simple graphical method to detect interlaboratory differences in accuracy and variability was observed.ObjectivesThe general goal of this work is to present a new exploratory methodology, graphical and easy to interpret, that can determine the accuracy and variability (precision) of a variable, and compare it to the methodology applied in ISO 5725-2 and ISO 13528.MethodsWe used confidence probability plots of the multivariate Student’s t-distribution to observe the accuracy and variability of microbiological measures carried out by different laboratories during a ring trial exercise. A function in R was built for this purpose: Miriam.analysis.ellipse(Y, factor_a, eel.plot = “ t-Student”). The different observations of accuracy and variability are represented in the ellipses. If any of the points are outside the ellipse with 95% confidence, we can assume a deviation in accuracy and / or variability.ResultsTwo examples are provided with real microbiological data (logarithmic unit reductions (LR) for Pseudomonas aeruginosa, Escherichia coli, Staphilococcus aureus, Enterococcus hirae, Candida albicans and microbial counts in water (WW)). The proposed new method allowed us to detect possible deviations in the WWMEA variable and we believe it has future application for the rapid control of microbiological measures.

Evaluación de las mediciones ambientales, a través de un ensayo de aptitud, de los laboratorios ambientales de Nicaragua y Costa Rica

Se realizó un ensayo de aptitud con la participación de 24 laboratorios ambientales, 12 nicaragüenses y 12 costarricenses, para darle continuidad al proyecto cooperación MIFIC-PTB “Mejora de los Servicios que Aseguran la Calidad para el Sector Agua de Nicaragua”. El propósito fue evaluar la competencia analítica de los laboratorios participantes y demostrar la capacidad técnica y científica del CIRA/UNAN al organizar y desarrollar un Ensayo de aptitud. Se elaboraron dos lotes de muestras con sus respectivos ensayos de homogeneidad y de estabilidad de acuerdo a la ISO 13528:2016, uno para la medición de conductividad eléctrica y otro para determinar dureza total, dureza cálcica, calcio y magnesio en solución acuosa. A partir de estos resultados, se estableció a cada magnitud un “valor asignado”, el estadístico utilizado para la evaluación fue el “z- puntaje”, que mide el desempeño relativo al sesgo. Las mediciones de dureza total y calcio presentaron un excelente desempeño, en cambio las mediciones de conductividad eléctrica, dureza cálcica y magnesio presentaron un buen desempeño. El CIRAUNAN-Managua, demostró su competencia técnica y científica al desarrollar el presente ensayo de aptitud, posicionándolo en ventaja para llegar a ser laboratorio proveedor de ensayos de aptitud en Nicaragua en un mediano plazo.