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Results for “Repeatability and Reproducibility”

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PubMed1997

Development of a semisynthetic cheese medium for fungi using chemometric methods.

The growth, color formation, and mycotoxin production of six cheese-related fungi were studied on nine types of natural cheeses and 24 semisynthetic cheese media and compared using principal component analysis. The semisynthetic cheese media contained various amounts of Ca, K, Mg, Na, P, Fe, Cu, Zn, lactate, lactose, and casein. A robust well-defined and easily prepared semisynthetic cheese medium was developed for Penicillium commune, the most frequently occurring contaminant on semihard cheese. Growth experiments on the medium were repeatable and reproducible. The medium was also suitable for Penicillium camemberti. The medium had the following composition: 100 g of casein, 8.3 g of 90% lactate, 7.9 g of lactose, 7.3 g of CaCl2.2H2O, 2.6 g of MgSO4.7H2O, 26.0 g of NaCl, 20 g of agar, 0.025 g of FeSO4.7H2O, 0.004 g of CuSO4.5H2O, and water to a total weight of 1 kg. The semisynthetic cheese medium was less suitable for Penicillium roqueforti, Penicillium discolor, Penicillium verrucosum, and Aspergillus versicolor. However, another semisynthetic cheese medium could be recommended for P. roqueforti and P. discolor. That medium had higher contents of P (5000 ppm, wt/wt), K (5000 ppm), and Zn (50 ppm) and lower contents of Na (2700 ppm), Fe (1 ppm), Cu (0.1 ppm), and casein (1%).

Caseins↗

PubMed2006

Development and evaluation of a one-step real-time reverse transcription polymerase chain reaction assay for the detection of salmonid alphaviruses in serum and tissues.

We designed 4 primer pairs to amplify conserved regions of the E1 or nsP4 genes of salmonid alphavirus (SAV) and evaluated their performance in optimized 1-step SYBR green real-time RT-PCR (RRT-PCR) assays. A single primer pair, amplifying a 227 bp segment of E1 was then chosen for further study. This RRT-PCR was shown to be highly repeatable and reproducible over a wide range of RNA dilutions, with a linear relationship between cycle threshold (Ct) value and RNA concentration over a 10(7) dilution range. The limit of detection was calculated to be < or = 1.5 TCID50 ml(-1). When applied to sera previously screened by virus isolation for SAV viraemia, the RRT-PCR correctly identified all 13 culture-positive samples, as well as finding an additional 28 sera positive. Relative semi-quantitation of sera showed a very highly significant relationship between copy number and TCID50 (p < 0.001, R2 = 0.9563). Following experimental infection of salmon, heart samples were consistently positive until 21 d post infection (dpi), with (weak) positive signals still detectable in 50% of fish 70 dpi.

Alphavirus↗

PubMed2005

[Inter-laboratory study for validation of a Japanese official analytical method for determination of patulin in apple juice].

To validate a modified version of AOAC official method of analysis 995.10 as an official standard in Japan for determination of patulin in apple juice, an inter-laboratory study was performed in 11 laboratories using a non-contaminated sample, 2 naturally contaminated samples and 2 spiked samples of apple juice. For naturally contaminated apple juices, the relative standard deviations for repeatability and reproducibility were 3.2, 7.1% and 10.0, 21.7%, respectively. HORRAT values were 0.4, 0.9. The average recovery of patulin from spiked sample was 83.7%. The limit of quantification was calculated as 10 microg/kg. From these results, the method was thought to be suitable as an official standard for determination of patulin in apple juice in Japan.

Chromatography, High Pressure Liquid↗

PubMed2026

Validation of the TransplantTrace cfDNA Kidney assay for measurement of donor-derived cell-free DNA in transplant recipients.

INTRODUCTION: Donor-derived cell-free DNA (dd-cfDNA) has emerged as a promising non-invasive marker for assessing allograft status and guiding clinical management in transplant recipients. Its utility in kidney transplantation has repeatedly been demonstrated in large studies showing a strong association between elevated dd-cfDNA levels and allograft injury or rejection. This study evaluated the performance of a centralized next-generation sequencing (NGS)-based assay for measurement of dd-cfDNA in patients post-kidney transplantation. METHODS: The TransplantTrace cfDNA Kidney assay utilizes 50 insertion-deletion (indel) markers to discriminate dd-cfDNA. Evaluation of analytical performance included determination of input requirements, analytical sensitivity and specificity, as well as accuracy and precision parameters. Diagnostic performance was evaluated in a retrospective cohort of 104 post-transplantation samples by comparing dd-cfDNA results with biopsy-confirmed rejection. RESULTS: The assay required low DNA input (2 ng) and demonstrated high analytical sensitivity, with a verified limit of detection of 0.2% and limit of quantification of 0.3% dd-cfDNA. Analytical accuracy was excellent (R 2 = 1.00), with high repeatability and reproducibility across the reportable range of 0.2-30% dd-cfDNA. In the clinical validation, the assay showed high concordance with biopsy-confirmed rejection and excellent discriminatory performance for differentiating active from non-active rejection (AUC of 0.980). At a 1% cut-off, the assay exhibited a positive predictive value of 100%, supporting confident identification of patients likely to have treatable graft injury, while a high negative predictive value (95.6% at 15% prevalence) supports its reliability in ruling out active rejection. CONCLUSION: The TransplantTrace cfDNA Kidney assay demonstrated robust analytical performance and strong clinical concordance with biopsy-confirmed rejection status. Its high diagnostic accuracy supports reliable identification and exclusion of active rejection, with the potential to reduce reliance on invasive biopsy procedures in patients with elevated serum creatinine but low dd-cfDNA levels. In summary, the findings of this study support the implementation and use of this centralized assay for measurement of dd-cfDNA in patients post-kidney transplantation.

centralized↗

PubMed2005

On audiovisual spatial synergy: the fragility of the phenomenon.

Recent literature has highlighted the importance and ubiquity of cross-modal links in spatial attention, whereby shifts in attention in one modality often induce corresponding shifts in other modalities. We attempted to provide further evidence for the case of audiovisual links during sustained endogenous attention by addressing several potential methodological confounds in previous demonstrations. However, we failed repeatedly to reproduce the phenomenon of spatial synergies between auditory and visual attention, found by Driver and Spence (1994) and frequently cited to support the automatic nature of cross-modal attention links. We discuss the results in light of recent evidence about cross-modal spatial links during sustained attention and support the idea that such links can weaken or even disappear under certain circumstances, such as during periods of sustained attention. The implication is that individuals can select inputs from different modalities from different locations more easily than previously had been thought.

Adult↗

PubMed1990

Humoral and cell-mediated immune responses to the Plasmodium falciparum antigens PF155/RESA and CS protein: seasonal variations in a population recently reexposed to endemic malaria.

Resurgence of falciparum malaria occurred in the Central Highlands of Madagascar in the 1980s and the disease is currently hyperendemic. We determined the humoral and cellular responses to synthetic peptides reproducing the repeat sequences of 2 major Plasmodium falciparum antigens: the Pf155/RESA and the circumsporozoite (CS) protein. Blood samples from 83 subjects living in a rural community near Antananarivo were obtained at the beginning and the end of the transmission season. At enrollment, 40 subjects presenting with and 43 without blood parasites had similar T cell proliferative response and antibody level to all antigens tested. However, P. falciparum-infected individuals exhibited a decrease in the absolute number of T lymphocytes, due to a diminished number of CD8+ and natural killer lymphocytes. The number of CD4+ cells was similar in both groups. In the overall population, 45% of subjects had a T cell response to at least 1 RESA peptide (29-35% responding to a given peptide) and 35% to the CS protein peptide. Thirty-two percent of the donors presented with RESA antibodies and 23% had CS protein antibodies. After 20 weeks, at the end of the transmission season, cellular proliferative responses to all antigens markedly decreased as evidenced by a decrease of both the number of responders and mean stimulation indexes. Humoral response to RESA, as detected by erythrocyte membrane immunofluorescence (number of responders and mean antibody titers) markedly increased. Humoral responses to the CS protein and RESA peptides were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Immunogenicity of the Plasmodium falciparum asexual blood-stage synthetic peptide vaccine SPf66.

The immunogenicity of the cocktail vaccine SPf66 against Plasmodium falciparum was investigated in rabbits, monkeys, and human volunteers. This polymerized peptide vaccine incorporates a portion of each of the 35-kD, 55-kD, and 83-kD blood-stage proteins, linked by an amino acid sequence reproducing one repeat from the circumsporozoite protein of P. falciparum. Results from this study show that vaccination with this vaccine molecule elicited high titers of antibodies to SPf66 and its constituents, but these antibodies did not correlate with regular or sensitive indirect fluorescent antibody (IFA) titers to blood-stage malaria parasites. However, rabbits injected with individual peptides produced antibodies with low affinity to indefinite parasite structures by immunoelectron microscopy, and rabbits injected with SPf66 had high antibody titers against the peptide (NANP)40. Consequently, these anti-SPf66 serum samples recognized P. falciparum sporozoites in the IFA. Such reactivity was not observed in monkeys or human volunteers vaccinated with SPf66. In addition, SPf66 components were recognized by antibodies induced by natural infection in humans and by laboratory-monitored infections in Aotus monkeys. These results suggest that this vaccine candidate merits further developmental work to better define immune response elicited by the copolymer to the parasite.

Adolescent↗

PubMed1998

MicroVal: a European approach to the certification of new microbiological methods.

In recent years, food microbiologists have seen the development of a range of nonstandard methods designed to enumerate or determine the presence of various microorganisms in food products. Generally the new methods are designed to give the microbiologist advantages, such as greater automation or faster results, over standard conventional methods. The new methods, however, have often not been thoroughly tested to give the end user confidence in the results. In order to generate data to show that new methods give results that are comparable with standard methods, they must be validated. A number of validation schemes have been developed in various countries throughout the world. There has not, however, been an acceptable scheme recognized throughout Europe. The MicroVal project has been involved in the development of a European microbiological method validation and certification scheme; it involves 21 partners from 7 EU member states. New methods that are tested by the MicroVal system will undergo initial testing in a single expert laboratory, to establish the test's specificity, limit of detection, relative accuracy, sensitivity, and linearity. This testing will be followed by a collaborative study in a minimum of eight laboratories, which will be used to determine the test precision, repeatability, and reproducibility. All results will be assessed by two expert reviewers who will recommend or reject the test. Tests that are recommended will be finally accepted by a MicroVal committee. The committee will pass its comments to one of several certification bodies (working together through a memorandum of understanding) who will certify that the new method gives results that are equivalent to the reference method used throughout the validation work. The technical rules that describe the work required to certify a method are currently being considered by the European Committee for Standardisation (CEN), with the objective that the rules will become a CEN standard for the certification of new test methods. When this objective has been achieved the rules will become an International Standards Organisation (ISO) standard for new test method validation.

European Union↗

PubMedDate not supplied

Dry rehydratable film method for enumerating confirmed Escherichia coli in poultry, meats, and seafood: collaborative study.

A rehydratable dry-film plating method for Escherichia coli, the Petrifilm E. coli/Coliform (EC) Count Plate in foods, has been compared with the AOAC INTERNATIONAL most probable number (MPN) method. Eleven laboratories participated in the collaborative study. Three E. coli levels in 8 samples each of frozen raw ground turkey, frozen raw ground beef, and frozen cooked fish were tested in duplicate. Mean log counts for the Petrifilm plate procedure were not significantly different from those for the MPN procedure for cooked fish samples inoculated with low or high inocula levels, for samples of raw turkey inoculated at medium level, and for beef inoculated at low, medium, and high levels. Repeatability and reproducibility variances of the Petrifilm EC Plate method recorded at 24 h were as good as or better than those of the MPN method. The dry rehydratable film method for enumerating confirmed E. coli in poultry, meats, and seafood has been adopted first action by AOAC INTERNATIONAL.

Animals↗

PubMedDate not supplied

A statistical evaluation of the Youden Matched-Pairs Procedure.

AOAC INTERNATIONAL currently permits investigators to use the Youden Matched-Pairs Procedure to obtain estimates of the method performance indicators repeatability and reproducibility (S(r) and SR, respectively). This report explains the statistical model assumptions upon which the procedure is based, provides validity tests for several of these assumptions, explains conditions under which Youdens' "precision error" is not consistent with precision estimate S(r) or SR as defined by AOAC INTERNATIONAL, and indicates when precision estimates based on the procedure should be interpreted with caution or should not be used.

Laboratories↗

PubMedDate not supplied

Validation of a gas chromatographic method for determining fatty alcohols that compose policosanol in five-milligram film-coated tablets.

A gas chromatographic method using a packed column and 1-eicosanol as an internal standard was developed and validated for determination of the aliphatic fatty alcohols that compose policosanol in 5 mg film-coated tablets. The alcohols were analyzed as trimethylsilyl (TMS) derivatives, prepared with N-methyl-N-trimethylsilylfluoroacetamide. The method can detect degradation products with high retention times without interfering with the peaks of the active principle. Good linearity (correlation coefficient = 0.9996) and accuracy (recovery = 100.44%) were proven over a range of 50-150% of the nominal concentration. Within-day and between-day precisions at the nominal 100% value met the acceptance criteria (< 2%). Ruggedness was examined through an intralaboratory experimental study in which 7 operational changes were made and the observed results were quantitation, repeatability, resolution, and relative retention time. Among these results, only the relative retention time (tC28,C20) was significantly affected when the column used was 2.1 m instead of 3.1 m. Repeatability and reproducibility (r = 0.1506 and R = 0.2450, respectively) were obtained from a uniform-level interlaboratory test. The method is suitable for quality control and stability studies of these tablets.

Anticholesteremic Agents↗

PubMedDate not supplied

Liquid chromatographic determination of residual nitrite/nitrate in foods: NMKL collaborative study.

Nitrite and nitrate are used as additives in the food industry to provide color and taste and to control undesirable gas and flavor production by anaerobic bacteria by virtue of their antimicrobial properties. The analytical method that has been widely used to determine nitrite and nitrate involves the use of toxic cadmium. In response to a request from the Nordic Committee on Food Analysis, a study was performed to obtain an alternative chromatographic method to determine residual nitrite and nitrate in meat products. The study was done in 3 stages: (1) comparative evaluation of the performance of 3 liquid chromatographic methods, (2) internal validation of the selected ion chromatographic method, and (3) a collaborative study in which 17 laboratories from European countries participated. Furthermore, the applicability of the method to matrixes other than meat and meat products was demonstrated. The results of the collaborative study show that the European Prestandard prENV 12014-4 is well suited for the determination of nitrite and nitrate in different foods (e.g., meat products, vegetables, baby food, and cheese). The limits of detection for nitrite and nitrate ions are 1 and 10 mg/kg, respectively. Recoveries of residual nitrite/nitrate ranged from 96 to 108%. Repeatability and reproducibility were satisfactory.

Anions↗

PubMed2000

Pulse wave velocity. A new calculation method.

BACKGROUND: The increase in aortic Pulse Wave Velocity (PWV) is considered a surrogate marker of vascular disease; it can be non-invasively assessed by means of an indirect method calculating the time that the pulse wave takes to travel a definite distance along the vasculature; the distance/time ratio corresponds to the velocity measure. The presentation of a new calculation method is the aim of the present study. METHODS: A duplex scanner at the common carotid artery, the abdominal aorta at the prebifurcation site and the femoral common artery levels, was performed on 127 out-patients with risk factors, 38 of which were affected by clinical vascular disease, and on 50 healthy subjects (control group). The spectral analysis from these three sites was registered simultaneously with an ECG trace and the interval between the R wave apex and the spectral complex systolic foot was measured. The Transit Time (TT) was calculated by the difference between the values obtained from the proximal and distal measurement sites and PWV dividing the distance between them by the TT (PWV = Distance/TT); statistical significance and intra and inter observer variation coefficient, expressed as mean +/- standard deviation, were calculated by the analysis of variance and Turkey test, the correlation with the major risk factors and the intima-media thickness by the multivariate analysis. RESULTS: The PWV is increased in the patients group compared to control group (p < 0.001). Multivariate analysis shows a positive correlation with age, hypercholesterolemia, arterial hypertension, diabetes mellitus, intima-media thickness and arterial disease, no correlation was found with the smoking habit. The "patients" group shows an increased PWV in those with atherosclerotic plaques and/or clinical vascular disease compared to non atherosclerotic patients with risk factors (p < 0.001); the intra and inter observer variation coefficient ranged between 4.87 +/- 1.82% and 8.06 +/- 3.16% respectively. CONCLUSIONS: The proposed PWV measurement method is simple, quick, reproducible and repeatable, it can separate healthy subjects from patients with risk factors, atherosclerotic plaques and clinical vascular disease. Due to the strong correlation with age, normal values in different age groups are necessary before the PWV can be used as a marker of vascular disease.

Adult↗

PubMed2000

Branched-chain keto-acids and pyruvate in blood: measurement by HPLC with fluorimetric detection and changes in older subjects.

BACKGROUND: Measurement of keto-acids is important in various clinical situations. The aim of the present work was to develop a rapid HPLC method for the determination of keto-acids in human serum and to assess the concentrations of these acids in young adults and institutionalized elderly adults. This method was applied to the determination of blood keto-acid concentrations of young adults and institutionalized elderly people, divided into age groups METHODS: Four keto-acids (alpha-ketoisocaproate, alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, and pyruvate) were derivatized with o-phenylenediamine to give fluorescent derivatives. After the sample preparation step (75 min to prepare 20 samples), the derivatives were separated chromatographically on a reversed-phase column using a binary gradient. RESULTS: The fluorometric detection of the four keto-acids was rapid, <12 min. The method is repeatable and reproducible: the CVs were <6% and <11%, respectively, for each of the keto-acids. We found no significant difference between males and females. Concentrations of the branched-chain keto-acids decreased after age 60 years, especially alpha-ketoisocaproate, which decreased approximately 40%. CONCLUSIONS: The proposed method allows rapid and reliable measurement of keto-acids. The data demonstrate that changes in branched-chain keto-acids concentrations in serum occur with age.

Adult↗

PubMed2000

[A statistical evaluation of the variability in the measurements of the resistive index in kidney transplantation].

INTRODUCTION: Doppler ultrasound (US) is a valuable tool to measure blood flow in the transplanted kidney, but its operator-dependence can greatly affect repeatability and reproducibility of measurements. Aim of this work was to evaluate intraobserver and interobserver variability in measuring the resistive index (RI) in renal transplants. PATIENTS AND METHODS: Ten renal transplant recipients were randomly selected among those undergoing follow-up and examined by two operators (FG and LB) with 3.5 MHz and 10 MHz scanheads to assess the variability of RI measurements. Each observer obtained two measurements of the RI with each scanhead within a 10-15 minutes' period. In all, 80 measurements were made, 4 per patient per observer. The statistical analysis included two-tailed Student's t-test for paired data and calculation of repeatability/reproducibility coefficients. RESULTS: Student's t-test analysis demonstrated a statistically significant difference (p = 0.037) between the means of the first and second measurements by FG with the 3.5 MHz scanhead and the first and the second measurements by LB with the same scanhead. Differences between the other means were not statistically significant. Intraobserver variability ranged 0.03 units (or 2.07%) and 0.07 units (or 4.24%), while interobserver variability was 0.04 units with both 3.5 and 10 MHz scanheads, or 3.61 and 3.73%, respectively. CONCLUSIONS: Doppler US of renal transplants has statistically quantifiable operator-dependent variability: the possible evidence of statistically significant differences can be minimized by having the same operator make the measurements. However, RI variations ranging 0.02 to 0.04 units should not be considered significant.

Adult↗

PubMedDate not supplied

Determination of crude fat in meat by supercritical fluid extraction: direct method: PVM 3:2000.

Meat samples are prepared by passing meat through a food chopper, bowl cutter, or food processor, subsampling the meat, and mixing the meat with granular diatomaceous earth. No drying step is necessary. Supercritical CO2 is then used to extract crude fat (which is defined as the components of meat that are extractable with petroleum ether, without digestion of the sample). Extracted material is deposited on glass wool contained in collection vials. After removal of any residual moisture from the extracts, percent crude fat is determined by weight gain of the collection vial. This method has been peer-verified by 3 laboratories, for a wide variety of raw and processed meat products containing 6-28% crude fat. Samples were prepared at the submitting laboratory. Ground samples were split into 4 portions, packed in Whirlpack bags, and immediately frozen. Frozen samples were sent by overnight room temperature, and percent fat was determined (in triplicate), without further processing of the samples. Analysis of the samples was completed within 1 week of sample prepara. tion. On the basis of this study, it can be estimated that all repeatability and reproducibility values are <3.0. Mean accuracy of the direct gravimetric supercritical fluid extraction method for meat samples ranged from +0.22 to -1.41 when the method was compared with AOAC Method 960.39. Interferences are unlikely but would include any nonfat substance that is added to (processed) meat, is soluble in nonpolar solvents, and is present in a quantity that would alter results. This method is expected to perform equally well for all meats with fat content within the stated range of applicability.

Animals↗

PubMedDate not supplied

Determination of arsenic in seafood by focused microwave digestion and hydride generation-atomic fluorescence detection.

A new method was developed for total arsenic determination in seafood products such as oysters, mussels, tuna fish, and algae. Matrix decomposition and oxidation to arsenate of all the arsenic compounds in the product were completed in 25 min by using a 3-step program of focused microwaves (40-120 W) with nitric and sulfuric acids. Quantitation was performed by hydride generation-atomic fluorescence detection (HG-AFS). Results of method optimization are presented and discussed. A detection limit <125 microg/kg arsenic was obtained; the quantitation limit was close to 400 microg/kg, with repeatability and reproducibility <5% relative standard deviation. Validation was performed by analyzing 4Reference Materials (arsenic concentration expressed as mg/kg): The National Institute of Standards and Technology SRM 1566a Oyster tissue (14.0 +/- 1.2); the Bureau Community of Reference (now Standard Measurements & Testing Program) CRM 278 Mussel tissue (5.9 +/- 0.2) and CRM 627 Tuna fish (4.8 +/- 0.3); and the International Atomic Energy Agency RM 140 Fucus sample (44.3 +/- 2.1).

Animals↗

PubMedDate not supplied

Voltammetric behavior and analytical applications of lomefloxacin, an antibacterial fluorquinolone.

Lomefloxacin was reduced on a dropping mercury electrode, producing one or more peaks, depending on the pH of the aqueous medium. Coulometric measurements gave an experimental value of 1 electron for the main peak. Electrolysis was followed by UV spectrophotometry and liquid chromatography (LC), showing that a new band at 413 nm appeared for the electrolysis product in an acidic medium. Furthermore, by using UV spectrophotometry, an apparent pKa value of 6.75 +/- 0.05 was obtained for lomefloxacin corresponding to the carboxyl moiety in the 3-position. For analytical studies, the differential pulse polarographic mode in 0.1 N HCl was selected. The repeatability and reproducibility of the method were adequate (coefficient of variation [CV], 0.51%). The calibration curve method was used for the lomefloxacin concentration range of 7.0 x 10(-6) to 7.0 x 10(-5)M. The detection and quantitation limits were 1.0 x 10(-6) and 6.9 x 10(-6)M, respectively. For purposes of comparison, both UV spectrophotometric and LC (with UV and fluorimetric detection) methods were developed. The polarographic method showed good selectivity with respect to both excipients and degradation products. The recovery study showed a CV of <2% and an average recovery of 99.5% and it was not necessary to treat the sample before analysis. The method was applied to the determination of the uniformity content of lomefloxacin commercial tablets. The polarographic method was also successfully applied to the quantitation of lomefloxacin in urine, and the renal excretion profile was also determined.

Anti-Infective Agents↗