Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Reference Standards”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,387 records · Page 77Linked to original sources
PubMed2001

Quantification of bacterial polysaccharides by the purpald assay: measurement of periodate-generated formaldehyde from glycol in the repeating unit.

We have adapted the purpald assay for measurement of bacterial polysaccharides (PS) containing substituted and/or unsubstituted glycol (SG or UG) in residues such as glycerol, ribitol, arabinitol, furanosyl galactose, and sialic acid. For the purpald assay of UG-containing PS, 50 microL of PS samples was consecutively reacted with 50 microL of 16 mM NaIO4 for 20 min, 50 microL of 136 mM purpald reagent in 2 N NaOH for 20 min, and 50 microL of 64 mM NaIO4 for 20 min in a 96-well tissue culture plate followed by a measurement of absorbance at 550 nm with a plate reader. For SG-containing PS, conversion of SG to UG with 25 micro;L of 0.3 N NaOH, 1 h at room temperature for de-O-acetylation followed by 25 microL of 0.6 M H2SO4, 1 h at 80 degrees C for acid hydrolysis of PS precedes the periodate treatment in the purpald assay. The concentration of the samples can be calculated from the sample absorbance and the reference standard curve constructed from the reference concentrations of the same PS (well-characterized) and their corresponding absorbance values assayed in the same plate. The purpald assay provides a tool in addition to the existing ones for the measurement of glycol-containing PS. Among the usefulness of this method are the determinations of the glycerol content in the phospho-glycerol-containing PS and the SG and UG contents and structural integrity in PS and conjugate vaccines.

Bacteria↗
PubMed2005

Evolution of ochratoxin A content from must to wine in Port Wine microvinification.

To study the evolution of ochratoxin A (OTA) content from must to wine during the making of Port Wine, grapes from the five most common varieties of Port Wine were harvested and combined in equal percentages in order to perform microvinifications. Three sets of assays were studied: a blank (A), where the most common Port Wine-making process was used; in the second (B), a solution of OTA was added to the initial must; in the third (C), the grapes were aspersed with an inoculating solution of OTA-producing fungi. Samples were collected, in duplicate, on four different occasions throughout the process. The influence of the addition of SO2 to the must was also assessed in each set. The quantification of OTA was based on the standard reference method for wines (European Standard prEN 14133), which includes clean-up via immunoaffinity columns and HPLC with fluorescence detection. The limits of detection were 0.076 microg/l for wine and 0.114 microg/l for must. The method was validated by assessing the precision, accuracy and by obtaining an estimate of the global uncertainty. Overall, the levels of OTA observed during the vinifications dropped by up to 92%, and no grapes used in this work were contaminated naturally.

Chromatography, High Pressure Liquid↗
PubMed2004

Single-field fundus photography for diabetic retinopathy screening: a report by the American Academy of Ophthalmology.

OBJECTIVE: To evaluate whether single-field fundus photography can be used as a screening tool to identify diabetic retinopathy for referral for further ophthalmic care. METHODS: A MEDLINE search of the peer-reviewed literature was conducted in June 2001 for the years 1968 to 2001 and updated in September 2003, yielding 145 articles. The search was limited to articles published in English. The Cochrane Library of clinical trials was also investigated. The authors reviewed the abstracts of these articles and selected 63 of possible clinical relevance for review by the panel. Of these 63 articles, the panel selected 32 for the panel methodologist to review and rate according to the strength of evidence. RESULTS: Three of the 32 articles reviewed were classified as level I evidence, and 4 were classified as level II evidence. Evidence from level I studies demonstrates that as a tool to detect vision-threatening retinopathy, single-field fundus photography interpreted by trained readers has sensitivity ranging from 61% to 90% and specificity ranging from 85% to 97% when compared with the gold standard reference of stereophotographs of 7 standard fields. When compared with dilated ophthalmoscopy by an ophthalmologist, single-field fundus photography has sensitivity ranging from 38% to 100% and specificity ranging from 75% to 100%. CONCLUSIONS: Single-field fundus photography is not a substitute for a comprehensive ophthalmic examination, but there is level I evidence that it can serve as a screening tool for diabetic retinopathy to identify patients with retinopathy for referral for ophthalmic evaluation and management. The advantages of single-field fundus photography interpreted by trained readers are ease of use (only one photograph is required), convenience, and ability to detect retinopathy. Further studies will be required to assess the implementation of single-field photography-based programs to confirm the clinical and cost-effectiveness of these techniques in improving population visual outcomes. Future research also should include establishing standardized protocols and satisfactory performance standards for diabetic retinopathy screening programs.

Academies and Institutes↗
PubMedDate not supplied

Migration of mineral hydrocarbons into foods. 1. Polystyrene containers for hot and cold beverages.

Mineral hydrocarbons are used as processing aids at levels between 0.3 and 3% by weight in crystal polystyrene articles, the food contact uses of which include the dispensing of hot and cold beverages from automatic machines as well as in 'fast-food' and catering establishments. The levels of migration of mineral hydrocarbons from polystyrene cups and glasses have been measured into aqueous food simulants as well as lager, beer, cola, sparkling apple juice, lemon barley water, coffee, hot chocolate, tea, lemon tea and chicken soup. For the cold beverages and simulants, no migration above 0.1 mg/kg was observed, and for the hot beverages and simulants no result greater than 0.5 mg/kg. Analysis was by capillary gas chromatography, using hydrocarbon internal standards calibrated against mineral hydrocarbon reference standards.

Beverages↗
PubMedDate not supplied

Screening for diabetic retinopathy by one-field, non-mydriatic, 45 degrees digital photography is inadequate.

PURPOSE: To evaluate the sensitivity and specificity of one-field, non-mydriatic, 45 degrees digital photography for screening for diabetic retinopathy compared to indirect ophthalmoscopy using a slit-lamp, the reference standard. METHODS: A total of 100 consecutive diabetic patients (200 eyes) who underwent digital fundus photography and ocular examinations from June 2002 to November 2002 were included in this retrospective study. The patients, recruited from a hospital-based, retina referral practice, underwent 45 degrees, non-mydriatic, digital fundus photography using a non-mydriatic fundus camera. One image was obtained focusing the mid fundus between the optic disc and the macula. The fundus images were printed and graded by endocrinologists and a retinal specialist separately. The patients also underwent complete standard ocular examinations as the reference method for determining diabetic retinopathy, including dilation of their pupils and slit-lamp biomicroscopy done by ophthalmologists. The sensitivity and specificity of the digital photographic method were calculated by comparison to the reference method. RESULTS: The sensitivity and specificity of the retinal specialist's diabetic retinopathy grades were 53.8 and 89.0%, respectively. The sensitivity and specificity of the endocrinologists' grades were 45 and 75.3%, respectively. The false negative rates were 22 and 21.5% for endocrinologists and the retinal specialist, respectively. CONCLUSIONS: Screening for diabetic retinopathy using one-field, non-mydriatic, 45 degrees digital photography is inadequate.

Adult↗
PubMed1976

Energy-dispersive x-ray fluorescence spectroscopy and inductively coupled plasma emission spectrometry evaluated for multielement analysis in complex biological matrices.

Energy-dispersive x-ray spectroscopy and inductively coupled plasma emission spectrometry were evaluated as methods for routine multielement analysis of biological material. Standard samples included Standard Reference Materials (National Bureau of Standards), compounded mixtures, and supplements that provided a wide range of elemental concentrations for analysis. Elements included in this study were Zn, Pb, Ni, Mn, Fe, Mg, Cu, Ca, As, Se, Br, Rb, and Sr. Standards were analyzed as unknowns by participating laboratories. The two methods were evaluated for sensitivity, precision, and accuracy, and the results compared to those obtained for atomic absorption spectrometric analysis of identical standard unknowns. Both methods compared favorably and both were determined to be highly reliable for such an application. Advantages and disadvantages of each method are compared and discussed.

Animals↗
PubMed1975

Radioimmunoassay for the simultaneous detection and quantitation of hepatitis B surface antigen and of the homologous antibody.

A solid-phase radioimmunoassay procedure is presented, which allows the simultaneous detection and quantitation of HB, Ag and of anti-HBs. This procedure involves short preliminary incubation of test sera and of negative controls with a standard HB, Ag. The standard HBs Ag is diluted, according to preliminary assays, in order to yield a count ratio to negative controls of 10 to 1. Therefore, a value of 10 is ascribed to the counts of positive controls (standard HBs, Ag + HBs-negative serum) and counts of all test sera are proportionally related. The values obtained are denominated HBs Units. Test sera are considered to be positive for HBs Ag or anti-HBs when the corresponding HBs Units are significantly higher or lower, respectively, than the average value of standard antigen controls. Including the reference standard HBs Ag controls in each set of assays ensures the quantitative reproducibility of results among different assays and among different laboratories. Titres of serum HBs Ag and anti-HBs can be expressed as end-point dilutions, simply by plotting the corresponding HBs Units on a nomography. This was drawn according to the indications emerging from analysis of the radioimmunoassay kinetics. Laboratory assays and the practical application of the combined procedure over several thousands determinations showed that the binding capacity of the solid-phase substrate used (small antibody-coated polystyrene tubes) is extremely homogeneous. Such homogeneity accounts for a very high accuracy and reproducibility of quantitative results.

Antibodies↗
PubMed2002

A general classification of water quality in Indian context.

Water quality criteria are developed on the basis of scientific information about the effects of pollutants upon a specific use of water. The criteria, therefore, are defined as the acceptable levels of concentrations of pollutants for a particular use and describe the water quality requirements for protecting aquatic biota and maintaining an individual water use e.g. drinking, bathing, irrigation, industrial etc. Various international and national agencies have defined water quality criteria for different uses of water in tropical/non-tropical regions e.g. European Community (EC) standards have been developed specifying the Guide Level and Maximum Admissible Level of pollutant concentration for three different uses of water vis-a-vis drinking, bathing and fish water. WHO standards are defined in terms of a Action Level, whereas, WQIHS, Teharan have defined standards as Acceptable Concentrations and Maximum Allowable Concentrations. In India, CPCB has defined five classes A to E specifying different levels of treatment required to these class of water for different uses such as drinking outdoor bathing, propogation of wildlife and fisheries, and irrigation and industrial cooling. Mostly the water quality parameters considered in defining these standards are pH, Temperature, Turbidity chlorides, SO4 NO3, BOD, DO, TDS, coliform and some of the important heavy metals. However, many other parameters are also considered by the individual agencies. Thus, it is seen that different agencies use different terminology for classification such as Guide Level, Action Level, Maximum Allowable Concentration and Acceptable Level etc. for defining the water quality criteria. Hence, it was felt that a common classification such as Excellent, Acceptable, Slightly Polluted, Polluted and Heavily Polluted water, is essential to know the water quality status. In this context, an attempt is made to define a common platform of water quality classification as given above considering the important indicator parameters and the standards suitable for Indian scenario. The CPCB criteria for different parameters has been given due consideration while defining the concentration levels in the newly defined classes. The parameters/classes for which criteria were not defined in CPCB standards, reference was made to the standards defined by other agencies. To each one of these classes integer values was assigned in geometric progression which indicate the level of pollution in numeric terms. These values were termed as class indices and form the basis for comparison of water quality from Excellent to heavily polluted. The mathematical expressions were fitted to concentration ranges/levels in each of these classes against the class index. Thus, given a set of observations on water quality in terms of the parameters considered in this work, the mathematical expressions for that parameter gives a numerical value indicating the status of water quality Excellent, Acceptable, Slightly Polluted, Polluted or Heavily Polluted water.

Humans↗
PubMed2004

Development and validation of a third generation allergen-specific IgE assay on the continuous random access IMMULITE 2000 analyzer.

In vitro determination of allergen-specific IgE (sIgE) represents an important aid in the diagnosis and treatment of allergy. Improvements in laboratory methodology--the development of second, and now third generation assays for sIgE--have brought about major advances in speed, convenience, performance, and in the standards for judging performance. In this study, following the NCCLS I/LA20-A guidelines, we evaluated the analytical performance of a quantitative chemiluminescent enzyme immunoassay for sIgE using the continuous random access IMMULITE 2000 system. Defining features of this "third generation" sIgE assay include a true zero calibrator with a detection limit and functional sensitivity of 0.1 and 0.2 kU/L, respectively. The use of liquid allergens allows for complete automation, fast binding kinetics between IgE and the natural allergenic protein conformations, and a time-to-first-result of 65 min. Stable reagents and the low nonspecific signal associated with the liquid allergens and centrifugal wash technique permit extension of the measuring range to 0.1-100 kU/L, based on lot-specific, factory-calibrated master curves standardized to the WHO 75/502 reference standard. The assay demonstrated good precision and linearity over its measuring range. Relative to a first generation RIA (mRAST, from Hycor), clinical sensitivity, specificity, and concordance were 88%, 92%, and 90%, respectively (n = 812). Quantitative comparisons to a second generation assay yielded a linear regression relationship of IMMULITE 2000 = 0.99 (Pharmacia FEIA) + 1.99 kU/L, r = 0.859 (n = 169).

Allergens↗
PubMed1992

Simplified continuity equation: a simple, accurate, and noninvasive method in the evaluation of aortic stenosis.

Traditional evaluation of aortic stenosis usually requires cardiac catheterization for estimation of aortic valve area by the Gorlin formula. However, it is invasive and has been shown to be inaccurate in the presence of aortic regurgitation or low cardiac output. Evaluation of aortic stenosis by Doppler echocardiography using a continuity equation has been proved to have excellent correlation with cardiac catheterization. It requires hand tracing and computer software for calculation of time velocity integral. Recently, a simplified continuity equation was introduced, which uses the peak velocities instead of time velocity integrals. It saves time and obviates the computer assistance. The purpose of this study is to evaluate its accuracy using the standard continuity equation as the reference standard. Seventy patients with pure or combined aortic stenosis were examined. There was an excellent correlation between these two methods (r = 0.979, 95% confidence interval: 0.978-0.980). The aortic valve area derived from the peak velocity method = 0.018 + 0.949 X aortic valve area derived from the time velocity integral. The difference between the two methods was 0.04 +/- 0.08 cm2 (mean +/- SD) with a 95% confidence interval of -0.12 to 0.20 cm2. Furthermore, the correlation still remained good even in the presence of significant aortic regurgitation or impaired left ventricular function. In conclusion, the simplified continuity equation is a safe, time-saving, and accurate method for the evaluation of aortic stenosis.

Adult↗
PubMedDate not supplied

[Autonomic neural functioning in children with the periodic syndrome].

The pathogenesis of periodic syndrome (recurrent abdominal pain, cyclic vomiting, headache and other equivalents of childhood migraine) is often related in the literature to a "neuro-vegetative dysfunction", by which occasional stimuli (environmental, metabolic, emotional) should find a particular somatic expression. The homeostatic role of the autonomic nervous system could be deficient in these cases, but systematic research has never been done to explore this hypothesis. We have evaluated the autonomic nervous function in 38 children (12 M, 26 F) with periodic syndrome, by cardiovascular autonomic function tests. They consist of ortho- and parasympathetic parameters obtained by ECG registration and pressure monitoring during deep breathing, Valsalva manoeuvre, lying to standing postural change, sustained handgrip. In the absence of adequate pediatric references values, we have previously standardized these tests in a population of 198 healthy children (94 M, 104 F), aged 8.3-15.7 years. Results have been compared with our standard reference values, matching them by t-test for independent data: in both sexes, significant differences have been found out in only one of 11 parameters (p < 0.05) of the autonomic tests performed. Children affected by periodic syndrome reveal a reduced heart rate variation in transition from the early orthosympathetic phase to the late parasympathetic one after lying to standing passage, showing a smaller fluctuation of autonomic feedback systems. The physiological meaning of this result is unclear. However, in children with periodic syndrome no prevalence of ortho- or parasympathetic systems is evident.

Adolescent↗
PubMed1996

A method for scoring denture plaque.

Many studies have reported on the comparative efficiency of denture cleaning materials in their ability to remove deposits from dentures, but because of the variety of scoring methods used it is often difficult to make direct comparisons between materials. It is important that any measurements obtained should not only be accurate, reliable and reproducible but that inter-examiner error should be kept to a minimum. In this work three operators were asked to score 'blind' the total amount of disclosed plaque on a whole denture using a 0-10 scale. The overall conclusions of this test was that of poor inter-examiner agreement. A second test was therefore undertaken at a later date using the same three operators and protocol but on this occasion each surface of the denture was evaluated by reference to a series of standard reference dentures painted to simulate plaque scores in the 0-10 range. This test showed there to be no significant difference in the plaque scores recorded by the three operators and that the plaque scores recorded on the polished surfaces were significantly lower than those on the teeth and fitting surfaces (F = 10.55, P < 0.001).

Aged↗
PubMedDate not supplied

Comparison of closed-vessel and focused open-vessel microwave dissolution for determination of cadmium, copper, lead, and selenium in wheat, wheat products, corn bran, and rice flour by transverse-heated graphite furnace atomic absorption spectrometry.

A method is described for the determination of Pb, Cd, Cu, and Se in cereal samples. An atomic absorption spectrometer equipped with a transverse-heated graphite furnace with Zeeman background correction was used for all determinations. Sample preparation was performed by closed-vessel microwave digestion using nitric acid and focused openvessel microwave digestion using nitric acid-hydrogen peroxide. Both techniques were evaluated by using 15 cereal reference materials and comparing results with certified or reference values for each element. Cereal reference standards obtained from the Community Bureau of Reference (Europe), the National Institute of Standards and Technology (USA), the National Institute for Environmental Studies (Japan), the National Research Centre for Certified Reference Materials (People's Republic of China), and the Canadian Grain Commission were used. Application of a series of t-tests, conducted according to Sidak's modified Bonerroni t-procedure, showed that both techniques yielded accurate results for cereal reference materials. Some differences from certified and reference values, however, were found for each element.

Bread↗
PubMed1978

A simple and rapid technic for radioimmunoassay and calculation of plasma steroid concentrations.

A simple RIA technic for plasma steroids is described: Extraction residues or reference standards are dissolved in 20 microliter ethyl alcohol, or 20 microliter of alcoholic plasma extracts are given directly into RIA tubes; 500 microliter tracer solution, containing a known tracer mass, and, after mixing, 500 microliter antiserum solution or buffer solution are added, followed by 20 min incubation at room temperature and 20 min standing in an ice bath. Free from bound activity is separated by charcoal coated florisil or silicagel. Plasma steroid levels are calculated by a simple equation. An immunologic equivalent to the tracer mass present in the reaction mixture serves as reference value. Drawing of standard curves is not necessary for every assay. The linear transformation used here allows the number of reference standards to be reduced. So also single samples can be analyzed with relatively low effort.

Estradiol↗
PubMed2003

Considerations on development, validation, application, and quality control of immuno(metric) biomarker assays in clinical cancer research: an EORTC-NCI working group report.

A major dilemma associated with immuno(metric) assays for biomarkers is that various kits employing antibodies with differing specificities and binding affinities may generate non-equivalent test results. Also, variation in sample processing and the use of different standards (reference material) may result in discordant test results. Therefore, assays and procedures should be standardized and the quality of biomarker assay results should be monitored by continuous between-laboratory proficiency testing of performance. External quality control requires an established network of expert laboratories in which the investigators interact freely and where technical issues are discussed. Although such networking is more often praised than practiced, we strongly endorse and advocate between-laboratory exchange of experience and information. The present study discusses analytical aspects of immuno(metric) biomarker assays and presents recommendations of the Receptor and Biomarker Group of the EORTC (European Organisation for Research and Treatment of Cancer) how such tests should be validated for first time and day to day use. Moreover, a model for an appropriate quality assurance program is presented.

Biomarkers, Tumor↗
PubMedDate not supplied

Measurement of voltammetric peak area and resolution of overlapping peaks in the simultaneous determination of copper, lead, cadmium, and nickel in environmental matrixes.

Peak area was used for the simultaneous determination of copper(II), lead(II), cadmium(II), and nickel(II) in environmental matrixes by differential pulse voltammetry. The voltammetric measurements were performed with a conventional 3-electrode cell and an ammonia-ammonium chloride buffer, pH 9.1, as the supporting electrolyte. The analytical procedure was verified first in aqueous reference solutions and later by analysis of the standard reference materials Estuarine Sediment BCR-CRM 277 and River Sediment BCR-CRM 320. The precision and accuracy of the method, expressed as the relative standard deviation and the relative error, respectively, were <5% in all cases; the detection limit for each element under the experimental conditions used was in the range 1-5 microg/L. In the case of mutual interference between neighboring elements, an analytical procedure is proposed that is based on the standard additions technique, which allows the resolution of the overlapping voltammetric peaks.

Ammonium Chloride↗
PubMed1985

Standardization of serological assays for parasitic diseases with schistosomiasis and toxocariasis as prototypes.

A standardized microtest plate enzyme-linked immunosorbent assay (ELISA) was developed using the microsomal fraction of adult worms of Schistosoma mansoni (MAMA) as antigen. A standard reference serum pool was prepared and arbitrarily designated as having 100 activity units per microliter. The precision of the test, the suitability as a standard of the reference serum pool, and the J index as a method of determining the significant level of reactivity were evaluated. The predictability of the assay for patients with S. mansoni infections and for non-schistosomiasis patients was 95%. Preliminary studies with the truly quantitative microtest plate kinetic ELISA indicate that this assay is suitable for standardization for schistosomiasis and toxoplasmosis. The need for WHO International Reference Sera with designated International Units and for well-defined batteries of sera for evaluating the specificity and sensitivity of assays was emphasized.

Antibodies↗
PubMed2004

NIST bullet signature measurement system for RM (Reference Material) 8240 standard bullets.

A bullet signature measurement system based on a stylus instrument was developed at the National Institute of Standards and Technology (NIST) for the signature measurements of NIST RM (Reference Material) 8240 standard bullets. The standard bullets are developed as a reference standard for bullet signature measurements and are aimed to support the recently established National Integrated Ballistics Information Network (NIBIN) by the Bureau of Alcohol, Tobacco and Firearms (ATF) and the Federal Bureau of Investigation (FBI). The RM bullets are designed as both a virtual and a physical bullet signature standard. The virtual standard is a set of six digitized bullet signatures originally profiled from six master bullets fired at ATF and FBI using six different guns. By using the virtual signature standard to control the tool path on a numerically controlled diamond turning machine at NIST, 40 RM bullets were produced. In this paper, a comparison parameter and an algorithm using auto-and cross-correlation functions are described for qualifying the bullet signature differences between the RM bullets and the virtual bullet signature standard. When two compared signatures are exactly the same (point by point), their cross-correlation function (CCF) value will be equal to 100%. The measurement system setup, measurement program, and initial measurement results are discussed. Initial measurement results for the 40 standard bullets, each measured at six land impressions, show that the CCF values for the 240 signature measurements are higher than 95%, with most of them even higher than 99%. These results demonstrate the high reproducibility for both the manufacturing process and the measurement system for the NIST RM 8240 standard bullets.

Algorithms↗