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At least 1,441 records · Page 80Linked to original sources
PubMed1991

Comparisons of standard curve-fitting methods to quantitate Neisseria meningitidis group A polysaccharide antibody levels by enzyme-linked immunosorbent assay.

We examined several of the more commonly used models (log-log, two forms of the logit-log, and the four-parameter logistic-log transformations) for forming standard or calibration curves by using a standardized enzyme-linked immunosorbent assay (ELISA). Assay range, accuracy, and error for each function were measured and compared. Antibody levels to Neisseria meningitidis group A polysaccharide were estimated by calculating antibody concentrations of a serially diluted standard reference serum of known concentration. Each function achieved a high squared correlation coefficient (r2 greater than 0.97), indicating a high degree of accuracy in forming the standard curves. However, when predicted antibody concentrations were compared with the known values, the log-log function exhibited the least precision, with extreme percentages of error occurring at several dilutions. A partially specified logit-log transformation performed better than the log-log model over a reduced range of standard dilutions. This indicated that a high r2 alone was not a reliable measure of the accuracy of the standard curve. Of the methods surveyed, the logistic-log and fully specified logit-log functions were the most accurate models for forming standard curves and for interpolating antibody concentrations from the standard curve. The accuracy of the fully specified logit-log function is highly dependent on the precise specification of two unknown quantities, the optical densities at zero and infinite concentrations, prior to fitting the model to a typical set of calibration data. The four-parameter logistic-log function was the preferred choice for quantitating N. meningitidis group A total polysaccharide antibody by using a standardized ELISA. The function does not require prespecification of any parameters before estimating the standard curve, and the four parameters are readily interpretable in terms of identifiable physical quantities. This model also has the advantage that it is easiest to visualize since it does not incorporate complex transformations of the optical density scale.

Antibodies, Bacterial↗
PubMedDate not supplied

Determination of chromium and molybdenum in medical foods by graphite furnace atomic absorption spectrophotometry.

Graphite furnace atomic absorption spectrophotometry was used to determine chromium and molybdenum in 7 medical foods from 5 manufacturers. Linear standard curves were obtained for both elements for concentrations between 5 and 25 ng/mL. Detection limits were 0.24 ng/mL for Cr and 0.67 ng/mL for Mo. Characteristic masses were 3.1 and 14.7 pg for Cr and Mo, respectively. No difference was detected between wet and dry ashing methods, and dry ashing was used to complete the study. The method was validated by assaying various National Institute of Standards and Technology standard reference materials. Analysis of these products for Cr and Mo were within certified values. One product was evaluated by this method for reproducibility (n = 5). Relative standard deviations were 6.8 and 4.8% for Cr and Mo, respectively. This product contained 0.31 +/= 0.02 micrograms Cr/g and 0.63 +/- 0.03 micrograms Mo/g. The remaining products contained 0.09-1.28 micrograms Cr/g and 0.07-2.3 micrograms Mo/g. Mean recovery values were 98 +/- 14% (n = 14) for Cr at spike levels of 0.20-1.89 micrograms/g and 102 +/- 24% (n = 10) for Mo at spike levels of 0.30-1.89 micrograms/g.

Animals↗
PubMed1989

[Metrological requirements for clinical laboratory studies].

The paper analyzes the foreign literature on the achievements and tendencies in the unification of measurements of physicochemical characteristics of biologic materials at laboratories for clinical diagnosis. Reviews the principles of creating a reference basis and an hierarchic system of measuring, reference, and working methods and devices, that should provide a transfer of the measured values from the reference values to working means of measurements. Discusses the contribution of the reference materials to the system of measurements of the biosample composition. Presents data on the standard reference material of the USA National Bureau of Standards for clinico-diagnostic laboratory studies.

Government Agencies↗
PubMedDate not supplied

Employment of peak area as instrumental datum for improving the voltammetric quantitative analysis of heavy metals in fresh and sea water in the presence of surfactants.

Peak area instead of peak height is used for the simultaneous determination of Cu(II), Pb(II), Cd(II), and Zn(II) in fresh and sea water in the presence of anionic and cationic surfactants by differential pulse anodic stripping voltammetry. These species, if present, tend to make more irreversible the electrodic process of the metals. Because the employment of peak area for species having irreversible electrodic processes permits limits of detection about one or 2 orders of magnitude lower, this work shows the possibility of determining heavy metals at ultratrace level concentrations in the presence of surfactants, compounds which are always present in natural waters. The precision and accuracy of the analytical method were checked by the analysis of the standard reference materials (SRM) Fresh Water NIST-SRM 1643d, Sea Water BCR-CRM 403, and Estuarine Water BCR-CRM 505. The former, expressed as relative standard deviation (s(r)), and the latter, expressed as relative error (e), were satisfactory, being in all cases lower than 5%. The analytical procedure has been applied to fresh and sea water sampled in the Po river mouth area (Italy).

Calibration↗
PubMed1998

Standardizing flow cytometry: a classification system of fluorescence standards used for flow cytometry.

The growing number of standards commercially available in the field of flow cytometry makes it difficult to know which standards to use to obtain a desired level of quality assurance. A classification system of fluorescence standards has been developed on the basis of their physical characteristics. In turn, these physical characteristics determine the ability of the specific standards to perform selected functions, such as alignment, target referencing, compensation, and calibration. Knowing the properties and limitations of specific standards will help flow cytometer users to select the appropriate standard for the application that they will be performing, especially in regard to intra- and interlaboratory quality assurance. Common protocols used in conjunction with specific classifications of reference standards can provide unified analysis regions or window of analysis across different instruments and/or laboratories. In addition, specific classifications of calibration standards can help select those standards that will provide independent and direct comparison of instrument performance parameters, especially in studies involving multiple laboratories. Knowledge and understanding of the classification system can guide flow cytometer users in more efficient and accurate instrument setup and quality control when conducting research, as well as clinical applications.

Calibration↗
PubMed1984

A study showing a high degree of interlaboratory variation in the assay of human interferon.

Identical human fibroblast interferon samples were assayed in four different laboratories, in all of which the international reference standards were used. Up to tenfold differences in titer were observed between the laboratories. Differences of this magnitude make meaningful comparisons of clinical and other interferon studies difficult and clearly indicate the need for an internationally accepted standardized interferon assay system.

Biological Assay↗
PubMed1998

National radioactivity standards for beta-emitting radionuclides used in intravascular brachytherapy.

The uses of beta-particle emitting radionuclides in therapeutic medicine are rapidly expanding. To ensure the accurate assays of these nuclides prior to administration, radioactivity standards are needed. The National Institute of Standards and Technology (NIST), the national metrological standards laboratory for the United States, uses high-efficiency liquid scintillation counting to standardize solutions of such beta emitters, including 32P, 90Sr/90Y, and 188Re. Additional measurements are made on radionuclidic impurities, half lives, and other decay-scheme parameters (such as branching decay ratios or gamma-ray abundances) using HPGe detectors and reentrant ionization chambers. Following such measurements at NIST, standards are disseminated in three ways: Standard Reference Materials (SRMs), calibrations for source manufacturers, and calibration factors for commercial instruments. Uncertainties in the activity calibrations for these nuclides are of the order of +/-0.5% (at approximately 1-standard deviation confidence intervals).

Academies and Institutes↗
PubMed2001

Identification of pharmaceutical glasses by laser ablation ICP-MS.

The chemical composition of pharmaceutical glasses (ampoules, infusion bottles, plunger) has been determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A Nd:YAG laser with 10 Hz repetition rate in the Q-switch mode at its fundamental wavelength (1064 nm) was used to identify common types of pharmaceutical glasses. The following isotopes were used for measurements: 7Li, 11B, 23Na, 24Mg, 27Al, 28Si, 29Si, 30Si, 39K, 42Ca, 47Ti, 57Fe, 90Zr, 121Sb, 137Ba. Each analysis included the measurement of 12 craters. Relative standard deviations between 1.8% and 8.0% of the quantitative results were obtained. 29Si was used as internal standard. Standard reference materials (soda-lime-, lead- and borosilicate glasses) were used for external calibration of laser sampling. Linear calibration functions for each isotope were found. All samples and standard materials were digested in a two-step-procedure by nitric/fluoric acid, then measured and externally calibrated by ICP-MS with multi-elemental standard solutions using 45Sc as internal standard. Digestion and laser ablation results agree within 8% (confidential interval 95%) with the certified values. Intensity ratios of most isotopes also agree sufficiently with the corresponding theoretical values (+/- 18%). The developed method allows to distinguish different types of pharmaceutical glasses.

Calibration↗
PubMed1998

Calibration of isotope ratio mass spectrometry working standard for 2H/1H ratio analysis.

A method is described for the calibration of an isotope ratio mass spectrometry working standard for 2H/1H analysis using highly purified (> 99.99% enriched) deuterium oxide (2H2O). Serial dilution of such a compound can be used to construct a standard curve for calibration purposes using the relationship [formula: see text] where APE is the atom percent excess. It was found that the determined rWR had a precision of +/- 1%. Most of the variation came from sample handling, which includes the serial dilution of the weighed deuterium oxide, the reduction of water to hydrogen gas and the introduction of the hydrogen gas into the mass spectrometer. The use of this calibration procedure allows the direct determination of the isotope ratio rSA, and APE from a standard curve over a wide range of enrichment. Unlike the reference standards V-SMOW and SLAP, the highly purified deuterium oxide is non-exhaustible and readily available. The highly purified deuterium oxide should be used in place of secondary standards to calibrate working references for 2H/1H analysis in biological studies.

Calibration↗
PubMed1953

International standardization of diphtheria toxoids.

The present report is an analysis of results of assays of diphtheria toxoids carried out over a four-year period at the Laboratory of Hygiene, Department of National Health and Welfare, Ottawa, Canada. A single preparation, a crude monovalent diphtheria toxoid, was used as a reference standard for all types of preparation (purified, crude, or adsorbed). The results suggest that the use of such a standard is justified even though there is evidence to show that adsorbed and plain toxoids, and toxoids of different grades of purity, do not have identical immunization curves. The merits of the present International Standard for Diphtheria Toxoid, Plain, for the assay of all types of toxoid are discussed. The results suggest that this is not particularly suitable for adsorbed preparations, probably because of its flatter immunization curve. For the latter preparations, the proposed international standard for diphtheria toxoid, adsorbed, should prove more practical and useful.

Biological Assay↗
PubMed2004

Standardless screening of chemical warfare agents based on gas chromatographic data.

A method for calculation of the retention time of a compound in a temperature-programmed mode of GC analyses is proposed. The method is based on a detailed consideration of thermodynamics of chromatographic process and account of the actual state of a capillary column. The suggested approach permits estimation of probability of a poisonous agent in tests by means of information stored in the database, eliminating a need for reference standard of such an agent.

Algorithms↗
PubMed1985

Methods of assigning accurate values to reference serum. Part 2. The use of definitive methods, reference laboratories, transferred values and consensus values.

Eight analytes (Ca, Cl, cholesterol, glucose, Mg, K, Na and urate) have been determined in one horse serum masterlot by up to six different procedures: (i) by so-called definitive methods; (ii) by a group of reference laboratories using a variety of analytical methods; (iii) using the results of two independent external quality assessment schemes; (iv) by transferring values from a human serum standard reference material analysed by definitive methods; (v) by similar transfer of values from several batches of horse reference serum previously analysed by definitive methods; and (vi) as in (v) but using a group of reference laboratories. The results have confirmed the validity and usefulness of the transfer process in value assignment and in identifying outliers due to inaccurate methods. Definitive methods are shown to be subject to error, and although they appear to be the most accurate single techniques currently available, they are not definitive in the sense of being without bias and having no known source of inaccuracy.

Animals↗
PubMed1995

Reference materials and reference measurement systems in laboratory medicine. Harmonization of nomenclature and definitions in reference measurement systems.

Reliability of clinical laboratory results is obtained through quality assurance in both their production and transmission. The former involves a reference measurement system of reference materials and reference measurement procedures with metrological and statistical verification of results. The latter requires that sender and receiver have access to a common terminology. Thus, two data banks are required. A plurilingual systematic vocabulary related to the reference measurement system, giving concepts with terms and definitions concerning measurement standards, reference measurement procedures, internal quality control, external quality assessment, probability and statistics-mainly based on existing authoritative publications. The material should be processed by standard scientific terminological procedure and offered to pertinent organizations and specialists for comment before finalization and authorization. A multilingual collection of systematic names for properties examined by the branches of Laboratory Medicine, such as clinical chemistry, clinical immunology, clinical microbiology, clinical pharmacology, haematology and blood banking, and histochemistry and cytology. The database should function as a reference to consultation and as a link in the transmission of data between local laboratory "dialects". This should be based on the ongoing comprehensive IUPAC/IFCC project for forming names in collaboration with relevant scientific organisations and area specialists. The relational data base including "run-time" software would be accessed by e-mail (gopher or other storage medium).

Chemistry, Clinical↗
PubMed1992

Ventilatory standards for clinically well aboriginal adults.

OBJECTIVE: To obtain reference standards for ventilatory function of clinically well Australian Aboriginal adults. DESIGN: A cross-sectional assessment of the population of a North Queensland Aboriginal community. SETTING: A specialist clinical and public health service. The measurements were made with the cooperation of the local primary health care centre. PARTICIPANTS: The 288 study subjects included over 70% of Aboriginal adults residing in an isolated Cape York community. Those with known respiratory disease, abnormal chest x-ray findings, positive loose cough sign, abnormal lung signs or inability to perform the ventilatory tests satisfactorily were excluded; 229 persons (80%) remained for analysis. Smoking was prevalent in both men (85%) and women (76%). As in most other studies producing reference values for lung function, smokers were not excluded. MAIN OUTCOME MEASURES: Age, standing height in bare feet and sitting height were recorded. Ventilatory measurements included forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and maximum mid-expiratory flow (MMEF) which is also known as the forced expiratory flow (FEF 25%-75%). RESULTS: Standing height, age and sex were the major determinants of ventilatory function. Sitting height was not a good predictor. Ventilatory values differed significantly from those expected for Europeans: Aboriginal lung volumes were much smaller (by about 25%) and fell much faster with age. The age-related decrease in lung function was less in smokers. CONCLUSION: The smoking effect may reflect the operation of differential survival or other selective factors and has been noted in some other ethnic groups. Although previous studies have yielded some ventilatory function data on Aborigines, we report the first population-based reference values expected for clinically well adults. The information will be useful to clinicians and public health workers.

Adult↗
PubMed1984

Perception--a problem in the grading of sacro-iliac joint radiographs.

Reliability in the assessment of radiographic abnormalities in the sacro-iliac joint was investigated by rheumatologists and radiologists experienced in the reading of such films. This study differs from previous ones in that films were masked to reduce cueing from the radiographic appearance of other pelvic bone and joint structures. Agreement was greatest (greater than or equal to 80%) when only the presence or absence of abnormality was considered. When corrected for chance, agreement on the individual radiographic abnormalities was frequently poor or modest. The use of reference radiographs reduced absolute disagreement and had a modest influence on absolute agreement. The scoring of films for epidemiologic purposes should preferably be delegated to senior radiologists using standard reference films. Nevertheless, there remains a considerable margin of error in the interpretation of sacroiliac joint radiographs which is of clinical and epidemiological importance considering the weight that radiographs of this joint carry in diagnostic rheumatology.

Ankylosis↗
PubMed1994

International collaborative study of the candidate international standards for human tumour necrosis factors alpha (hTNF-alpha) and beta (hTNF-beta) and for murine tumour necrosis factor alpha (mTNF-alpha).

Four ampouled preparations of human tumour necrosis factor alpha (hTNF-alpha), one ampoule of human tumour necrosis factor beta (hTNF-beta) and one ampoule of mouse tumour necrosis factor alpha (mTNF-alpha) were evaluated by 20 laboratories in nine countries for their suitability to serve as international standards for these materials. A further three preparations of recombinant hTNF-alpha were included in the study so that hTNF-alpha preparations from different sources and with various structures could be compared. The preparations were assayed using in vitro bioassays and immunoassays. On the basis of the results reported here, with the agreement of participants in the study and with the authorisation of the Expert Committee on Biological Standardization (ECBS) of the World Health Organization (WHO), the preparation of hTNF-alpha in ampoules designated 87/650 was established as the international standard for hTNF-alpha with a defined potency of 40,000 international units per ampoule. Estimates relative to hTNF-alpha for both hTNF-beta and mTNF-alpha showed a substantial inter-laboratory variability in cytotoxic activity indicating that no preparations of hTNF-alpha would be suitable as a reference standard for either hTNF-beta or mTNF-alpha. However, given the current need for reference preparations for these materials, the ampouled preparations of hTNF-beta (87/640) and mTNF-alpha (88/532) were assigned potencies in arbitrary units and are available as reference reagents.

Animals↗
PubMed1986

The preparation and testing of the proposed International Reference (IRP) Bermuda grass (Cynodon dactylon)-pollen extract.

A lyophilized candidate extract of Bermuda-grass (Cynodon dactylon) pollen, intended for use as an International Reference Standard, was prepared by pooling four individual candidate extracts. In preliminary investigations, the four candidate extracts encompassed a variety of extraction methods. The collaborative testing program simultaneously analyzed the proposed reference and the individual extracts and included 11 laboratories performing RAST inhibition, histamine release, crossed immunoelectrophoresis, crossed radioimmunoelectrophoresis, isoelectric focusing, sodium dodecyl sulfate gel electrophoresis, and protein determinations with a variety of reagents and methods. The four candidate extracts and the pooled reference were found to be equivalent. The stability of this extract has also been studied. This International Reference Preparation of Bermuda grass-pollen extract should be useful for research and industry.

Allergens↗
PubMed2006

A dosimetric analysis of interstitial intensity modulated implants for pelvic recurrences, base of tongue and orbita tumors with specific references to the ICRU-58.

BACKGROUND AND PURPOSE: In this article the conversion of the dosimetry of three different kinds of IMBT (intensity modulated brachytherapy) implants into ICRU-58 formalism is presented. The results allow an inter-study comparison of relative reference doses between different sites. PATIENTS AND METHODS: The evaluation included 76 patient plans: (a) 31 pelvic recurrences, (b) 30 base of tongue tumors, and (c) 15 orbita tumors were analysed retrospectively and the mean central doses (MCD) and relative reference doses were evaluated. RESULTS: The reference doses D(ref) normalized to the mean central doses of three subgroups resulted in (a) 66%, (b) 68%, and (c) 52%. This is in contrast to the generally proposed standard reference dose of 85% of the Paris system. CONCLUSIONS: Reduction of the reference dose yields to higher dose inhomogeneities and affects the positive local tumor control. It was found that in IMBT implants the 85% reference dose of the Paris system is suitable for reporting purposes but not necessarily for dose prescription. Consequently, in IMBT implants the prescription dose of 85% should be critically used.

Adolescent↗