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PubMed1984

Human proinsulin standards.

Two new batches of pancreatic human proinsulin have been compared with biosynthetic human proinsulin. Standards of these three proinsulin preparations were made on the basis of quantitative amino-acid analyses and compared in two proinsulin radioimmunoassays with a proinsulin standard prepared 14 years ago. The curves of the new standards were superimposable. However, they differed considerably from the curve of the old standard which proved to be only one-third of the strength of the new standards, thereby leading to a threefold over-estimation of proinsulin concentrations when the old standard is used. We conclude that the new standards should replace previously used standards.

Amino Acids↗
PubMed2005

Standardization of orthodontic products--does it make sense?

Since 1994, the DIN (Deutsches Institut für Normung e.V.) has had a German working group named "Orthodontic Products" working toward establishing standardized norms for orthodontic products. In the USA, a similar working group called "Orthodontic Materials" was established in 1996 at the ADA (American Dental Association). Working at the ISO level since 1997, an international team has been in charge of unifying the standards already set at national levels. It is the aim of this article to report on the current state of standardization in Germany and internationally. The standards already published for wires (DIN 13971, ADA Spec. 32), for brackets and tubes (DIN 13971-2, ADA Spec. 100) and for elastomeric elements (DIN 13901) have been considered, as have problems occurring with ISO standards (ISO/CD 15841 and ISO/CD 15841-2) and DIN 13904-1. We demonstrate that the demands made of these products by the orthodontists who use them have lead to reasonable quality standards. Thanks to clearly-defined testing methods, orthodontic products can now be tested and their compliance with these minimum standards can be compared. In fact, the standards that have been agreed upon help both the product manufacturers and their users to improve product quality and, ultimately, the success of orthodontic treatment.

Dental Materials↗
PubMed2005

Long-term stability of hydrocarbons in NIST gas standard reference material (SRM) 1800.

A gas standard reference material (SRM) containing fifteen hydrocarbons in nitrogen at a nominal 5 nmol mol(-1) was issued in 1993. The certification period for SRM 1800 was assigned as 2 years, because of limited stability data. Over a period of 10 years reanalysis of the lot standard (a sample chosen from the SRM lot to which all other lot samples are compared), SRM samples remaining in stock for sale, and SRMs returned to the National Institute of Standards and Technology (NIST) for recertification, were compared with primary standards to assess the stability of the hydrocarbons. New primary standards were periodically introduced into the original primary standard suite to assess the stability and consistency of the primary standards. Over this ten-year period 11 SRM 1800 samples were reanalyzed, resulting in 210 amount-of-substance fraction (concentration) determinations performed for quality-assurance purposes. Of these measurements 209 (99.5%) agreed within the original 95% confidence interval of the +/-4% expanded uncertainty, demonstrating the stability of the standards. There was also agreement to within +/-2% of the original concentration for 204 (97%) of the measurements. This is well within the original +/-4% expanded uncertainty assigned to the hydrocarbon concentrations at the approximate 95% confidence interval demonstrating stability. These results will enable the expiry date to be increased for future restock issues of SRM 1800.

Environmental Monitoring↗
PubMed1988

World Health Organization International Standards for highly purified human, porcine and bovine insulins.

The 4th International Standard (IS) for Insulin, established in 1958, consists of a mixture of relatively impure bovine and porcine insulins and is not suitable as a standard for the assay of highly purified single-species insulins presently used in the treatment of diabetes. Preparations of human, bovine and porcine crystalline insulins, representative of current highly purified therapeutic insulins, have now been studied in an international collaborative study carried out by twenty-three laboratories in fifteen countries. In the collaborative study described here, each of the three preparations was found to be suitable for use as a standard for insulin for bioassay and each was established by WHO in 1986 as an international standard. The 4th IS of Insulin bovine/porcine (code numbered 58/6) has been discontinued. Insulin preparations should now be calibrated in terms of International Units defined by the standard for the appropriate species: the International Standard for Insulin, Human, the International Standard for Insulin, Bovine, or the International Standard for Insulin, Porcine.

Animals↗
PubMed2005

Standardization of uveitis nomenclature for reporting clinical data. Results of the First International Workshop.

PURPOSE: To begin a process of standardizing the methods for reporting clinical data in the field of uveitis. DESIGN: Consensus workshop. METHODS: Members of an international working group were surveyed about diagnostic terminology, inflammation grading schema, and outcome measures, and the results used to develop a series of proposals to better standardize the use of these entities. Small groups employed nominal group techniques to achieve consensus on several of these issues. RESULTS: The group affirmed that an anatomic classification of uveitis should be used as a framework for subsequent work on diagnostic criteria for specific uveitic syndromes, and that the classification of uveitis entities should be on the basis of the location of the inflammation and not on the presence of structural complications. Issues regarding the use of the terms "intermediate uveitis," "pars planitis," "panuveitis," and descriptors of the onset and course of the uveitis were addressed. The following were adopted: standardized grading schema for anterior chamber cells, anterior chamber flare, and for vitreous haze; standardized methods of recording structural complications of uveitis; standardized definitions of outcomes, including "inactive" inflammation, "improvement'; and "worsening" of the inflammation, and "corticosteroid sparing," and standardized guidelines for reporting visual acuity outcomes. CONCLUSIONS: A process of standardizing the approach to reporting clinical data in uveitis research has begun, and several terms have been standardized.

Humans↗
PubMed2006

Does a stable isotopically labeled internal standard always correct analyte response? A matrix effect study on a LC/MS/MS method for the determination of carvedilol enantiomers in human plasma.

A stable isotopically labeled (SIL) analogue is believed to be the most appropriate internal standard in a quantitative bioanalytical liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay. It is assumed that a SIL internal standard always compensates for variability in chemical derivatization, sample extraction and LC/MS/MS analysis due to its nearly identical chemical and physical properties to the unlabeled analyte. Hence, the analyte to internal standard peak area ratio should be constant despite any variations in sample processing or analysis. However, in our laboratories, a deuterium labeled internal standard of carvedilol demonstrated an unexpected behavior-the analyte to internal standard peak area ratio changed with two specific lots of commercially supplied human plasma. Several experiments, including dilution of the extract with LC mobile phase and post-column infusion of the carvedilol solution followed by the injection of extracted blank plasma, have indicated that a high level of matrix suppression affected the ionization of the carvedilol-S enantiomer and its deuterated internal standard differently in these two lots of plasma. For the first time, it was clearly demonstrated that a slight difference in retention time between the analyte and the SIL internal standard, caused by deuterium isotope effect, has resulted in a different degree of ion suppression between these two analogues. This difference was significant enough to change the analyte to internal standard peak area ratio and affect the accuracy of the method.

Adrenergic Antagonists↗
PubMed1980

Development of a provisional reference human cord serum standard for alpha-fetoprotein determination.

A lyophilized human cord serum secondary reference standard (988 vials of 1 mL/vial) has been prepared at the Laboratory Centre for Disease Control (L.C.D.C.) in Ottawa to assist in the standardization of AFP determinations. HBSAG-negative lots of cord serum were used to prepare the standard. The moisture content of the freeze-dried material was less than 0.5 percent. AFP mass calibration standards were prepared by direct weighing in duplicate of highly purified freeze-dried material. Two RIA calibration runs were conducted on the reference cord serum employing the WHO First International Standard for AFP (72/225) and L.C.D.C. mass standards. Parallelism of dose response curves within assays was demonstrated between reference cord serum and mass standards and between the latter and the WHO standard. The mean WHO kIU of AFP per vial of reference serum (+/- coefficient of variation) was 63.0 +/- 6.4 and the mean mass of AFP determined as micrograms per vial was 80.7 +/- 7.9. A small-scale (pilot) interlaboratory calibration of the reference cord serum in mass units resulted in heterogeneous AFP estimates which ranged from 54.4 to 80.7 micrograms/vial. Greater uniformity of the latter results was noted following conversion of the mass estimates to WHO international units conversion factors provided by several laboratories.

Fetal Blood↗
PubMed1998

Comparison of p-fluoroketorolac and [18O3]ketorolac for use as internal standards for the determination of ketorolac by gas chromatography/mass spectrometry (GC/MS).

A chemical and a stable-isotope analog, p-fluoroketorolac and [18O3]ketorolac respectively, were directly compared for applicability as internal standards for the determination of ketorolac in plasma samples using gas chromatography/mass spectrometry (GC/MS) with selective-ion-monitoring detection, following derivatization to form the methyl esters. This comparison involved analyzing ketorolac calibration standards and spiked plasma samples that contained both internal standard candidates. The response for ketorolac and each internal standard was monitored simultaneously and electronically integrated peak heights were obtained. Thus, for each analysis performed, a response ratio was obtained for each internal standard relative to an identical ketorolac response. Linearity of response for ketorolac calibration standards and accuracy for spiked plasma sample analysis were compared using each internal standard. The use of [18O3]ketorolac as the internal standard provided superior accuracy data for the analysis of ketorolac in plasma samples.

Analgesics, Non-Narcotic↗
PubMed2000

Validation and implementation of an internal standard in comet assay analysis.

The comet assay is widely used to detect DNA damage in single cells. However, only moderate attention has been paid to the experimental variability of this assay, especially during electrophoresis. To take into account this variation and to be able to compare measurements from different electrophoretic runs, as would be necessary when large numbers of samples need to be analysed, it is important to integrate an internal standard into the assay. This study presents a first step in the validation and implementation of an internal standard in the alkaline comet assay. Untreated and ethyl methanesulfonate treated cells (K562 human erythroleukemia cell line) were used as negative and positive internal standards, respectively, in each electrophoresis run. Three steps were followed: (1) assessment of the different levels of variability which may influence the damage levels of the internal standards, (2) evaluation of the variability across separate electrophoresis runs on the quantification of DNA damage in the internal standards by three experimenters involved in different studies and (3) proposal of an adequate calculation system to integrate the internal standards into test sample data. The application of the two proposed models to samples from a human biomonitoring study is presented. The model which calibrates the measurements against the negative internal standard is the most useful since this negative standard was the most stable across experiments and among the three experimenters. The percentage of DNA in the tail is the most appropriate parameter to analyse induced DNA damage, because its interelectrophoresis and interexperimenter variation is less pronounced than that of tail length.

Comet Assay↗
PubMed2003

Analysis of biological samples by gas chromatography-mass spectrometry without a reference standard: measurement of urinary 18-hydroxytetrahydro-11-dehydrocorticosterone excretion rate in human subjects.

Reference standards for some minor urinary steroid metabolites are sometimes unavailable. We describe a novel procedure to quantitate a urinary steroid metabolite of known structure and mass spectrum, using as a standard a compound which produces ions in common with it and has a similar retention time in gas chromatography-mass spectrometry. The steroid of interest was 18-hydroxy-11-dehydrotetrahydrocorticosterone (18-OH-THA), the major urinary metabolite of 18-hydroxycorticosterone (18-OH-B), a putative intermediate in the conversion of 11-deoxycorticosterone to aldosterone. The steroid used as an alternative to the authentic 18-OH-THA standard was beta-cortol which, like 18-OH-THA, produces a fragmentation ion at m/z 457. Allo-tetrahydrodeoxycorticosterone (5alpha-THDOC) was used as the internal standard. beta-Cortolone also has the fragmentation ion at m/z 449 (in common with beta-cortol) and an authentic standard is available commercially. To validate the procedure, we quantitated beta-cortolone urinary excretion rate against this alternative standard and also against authentic beta-cortolone standards. Both methods produced similar results (adjusted R(2): 0.998, P<0.001). The method was then used to measure urinary excretion of 18-OH-THA rate in healthy volunteers. The reference range obtained was 20-204 microgram/24 h (n=32). This is similar to the few results available by conventional assay. Method performance was also similar to other assays of urinary steroids. This procedure could be generally applicable for assays when authentic standards are not available but mass spectra are known or can be predicted.

18-Hydroxycorticosterone↗
PubMed1999

Accurate determination of the number of CAG repeats in the Huntington disease gene using a sequence-specific internal DNA standard.

We have developed a sequence-specific internal DNA size standard for the accurate determination of the number of CAG repeats in the Huntington disease (HD) gene by cloning key fragments (between 15 and 64 CAG repeats) of the HD gene. These fragments, pooled to produce a sequence-specific DNA ladder, enabled us to observe the true number of CAG repeats directly, with no need for calculations. Comparison of the calculated numbers of CAG repeats in the HD gene using this sequence-specific DNA standard with a commercially available standard (GENESCAN-500 TAMRA) showed that the latter underestimated the number of CAG repeats by three when analyzed by capillary electrophoresis on the ABI 310 Genetic Analyzer (POP4 polymer). In contrast, the use of the same standard overestimated the number of CAG repeats by one when the samples were analyzed by denaturing polyacrylamide electrophoresis on ABI 377 DNA Sequencer (6% denaturing polyacrylamide gel). This suggests that our sequence-specific standard provides greater accuracy for the determination of the true number of CAG repeats in the HD gene than commercially available standards. The sequence-specific standard can be radioactively labeled and successfully replace conventional DNA size standards when analyzing polymerase chain reaction (PCR)-amplified HD alleles by denaturing polyacrylamide electrophoresis.

Alleles↗
PubMed2006

[Clinical evaluation of a new tonometer on the basis of international standard ISO 8612].

BACKGROUND: There is a continuous process of development of new tonometer types following different measurement principles on the tonometer market. A new tonometer working on the dynamic contour measurement principle is currently available for ophthalmologists. This device has special properties, since it determines the intraocular pressure as well as the ocular pulse amplitude. So far, clinical comparison measurements exist between the new tonometer Pascal and the applanation tonometer by Goldmann albeit without any reference to a standard. Besides, these measurements cover only a small pressure range between 7 mmHg and 23 mmHg which is not sufficient for medical diagnosis. PATIENTS AND METHODS: This new tonometer was investigated by clinical comparison measurements according to the currently valid international standard for human eye tonometers (ISO 8612). The tested tonometer determines the intraocular pressure without fluorescein. In an ophthalmogical hospital in Berlin the clinical comparison measurements were carried out by ophthalmologists on 127 patients according to the methods and criteria of the above-mentioned standard. A calibrated AT 870 from the Haag-Streit company served as reference tonometer. RESULTS: The different cornea surface geometries of individual eyes, the variation of tear liquid volume, and also the different elastic properties of the human eye due to a large variation in rigidity led to measurements of intraocular pressure by this tonometer with an excessively high number of outliers p (i) (i = 1, ..., 3) per group (p (1) = 16.28 %, p (2) = 8.85 %, p (3) = 15.69 %, 5.0 % outliers per group only are permitted for the differences method), which do not correspond to the requirements of the international standard for tonometers ISO 8612. This is also shown by application of total method of least squares of regression line (slope a = 0.964, interception b = 2.868 mmHg, standard deviation s (y) = 2.628 mmHg). CONCLUSIONS: The test of conformity of results of clinical comparison measurements to the international standard for tonometers ISO 8612 is the target of this work. The measurement results of the investigated tonometer are analysed and discussed according to this standard. Statements about the medical application of this medical measurement device for ophthalmologists are presented. According to the presented investigations the requirements of this international standard are not fulfilled by the tonometer Pascal.

Equipment Design↗
PubMed1997

Composite neuropsychological batteries and demographic correction: standardization based on equivalent scores, with a review of published data. The Italian Group for the Neuropsychological Study of Ageing.

Equivalent Scores (ES; Capitani & Laiacona, 1988) is a 5-point scale that offers a solution to the problem of standardizing neuropsychological scores after adjustment for age and education, given that the common z-standardization is not generally applicable in these cases. ES are discussed, and their properties and limits are compared with those of z-standardization. In a battery of ES-standardized tests, the average ES (AES) for the whole battery can provide a measure of the overall cognitive level, free of the influence of age and education. We report empirical data from a battery composed of 10 ES-standardized tests, in order to discuss general properties of ES standardization. The expected mean of the AES is constant, regardless of the number or type of tests included. The standard deviation of the AES, however, is variable: it decreases in proportion to the number of tests, but increases in proportion to their intercorrelation. We provide general indications concerning the normality threshold, which are applicable to all batteries of ES-standardized tests regardless of the number and type.

Adult↗
PubMed2001

Evaluating a visual field screening test for glaucoma: how the choice of the gold standard affects the validity of the test.

OBJECTIVE: To examine the effects of the gold standard on sensitivity, specificity, and area under the ROC curve when determining the validity of a screening test. METHODS: Fifty-eight people were recruited from a Veterans' Administration eye clinic. Screening included testing with the 26-point oculokinetic perimeter (OKP). We used different gold standards to categorize patients as positive or negative for glaucoma. The glaucoma hemifield test (GHT) and corrected pattern standard deviation (CPSD) from the Humphrey visual field analyzer (HVF) were used as objective gold standards. Ophthalmologist review of the HVF, using two different methods for classifying visual field defects, was also used as a gold standard. RESULTS: Using the review of the HVF that included mild, moderate, or severe defects, the area under the ROC curve was not significantly different from 50%. However, for all the other gold standards, the area under the ROC curve was significantly different from 50%. CONCLUSIONS: In determining the ability of the OKP to differentiate between glaucoma and normal subjects, the choice of a gold standard led to different conclusions about its usefulness as a screening test for glaucoma. Furthermore, sensitivity and specificity varied widely depending on which gold standard was used, and what cutoff point was used for the OKP. Although clinician review of the HVF may be used when specific criteria are given to define visual field defects, using objective measures from the HVF is easier and will allow for better comparisons between studies.

Aged↗
PubMed1995

CEN Standards for Testing and Certifying Personal Protective Equipment-Status Quo and Deficiencies: Examples.

By establishing the internal market, the European Union intended to create an area in which safety and health at work are guaranteed. For this purpose, a series of directives was passed. The EC Directive 89/686/EEC "Approximation of the laws of the Member States relating to personal protective equipment" is of particular interest to the manufacturers of personal protective equipment (PPE). On the European level, harmonized standards, that put these basic health and safety requirements into more concrete terms have to be available. The European Standardizing Committee (CEN) is charged with the elaboration of European standards. A total of 176 standards relating to personal protective equipment have to be setup; 57 of them are available at present. All CEN members are obliged to transpose them without modification into national standards. Formerly existing national standards have to be withdrawn. Existing European standards sometimes show deficiencies regarding the specification of requirements according to Directive 89/686/EEC: the standardization of PPE for special fields of application and insufficient harmonization of provisions for different PPE serving the same protective purpose. Test methods are not always described precisely enough.

European directives↗
PubMed2004

Implementation of standards for individual monitoring in Europe.

A large number of standards are available for radiation protection and individual monitoring purposes. They are published by various organisations, international and national. Moreover, the increasing policy of "Quality" applied to individual monitoring requires the implementation of standards on Quality Assurance (QA) both in technical and management aspects of a dosimetric service. Implementation of standards is not mandatory; therefore, varying degrees of implementation can be found in different European countries. However, for a number of good reasons, a degree of harmonisation within the European Union (EU) of the requirements and procedures for individual monitoring would be desirable. Harmonisation as applied to dosimetric services does not mean that they should all follow exactly the same procedures, but that they should aim to meet the same general requirements, and their results should be comparable. This article aims to compile information on the use of all standards applied within individual monitoring practices, be it on the calibration of dosemeters or on the QA procedures to be applied to the overall dose evaluation process. Both "technical standards" and "quality standards" will be discussed. A list of documents of relevance to subjects such as recommendations and requirements in the field of individual monitoring, whose application could help in the harmonisation of procedures, will also be given. As it is agreed that implementation of quality standards is a relevant framework within which harmonisation can be achieved, guidance on the implementation of quality standards in a dosimetric service is given. Accreditation and approval of dosimetric services will be of relevance in the process of harmonisation of individual monitoring within the EU. In this article, a discussion of various procedures and the meaning of both forms of recognition is also provided. Although most of the text applies to the monitoring of internal and external exposure to ionising radiation, the emphasis of this practical guidance is on monitoring for external radiation with passive dosemeters.

Body Burden↗
PubMed2003

Marginal structural models as a tool for standardization.

In this article, we show the general relation between standardization methods and marginal structural models. Standardization has been recognized as a method to control confounding and to estimate causal parameters of interest. Because standardization requires stratification by confounders, the sparse-data problem will occur when stratified by many confounders and one then might have an unstable estimator. A new class of causal models called marginal structural models has recently been proposed. In marginal structural models, the parameters are consistently estimated by the inverse-probability-of-treatment weighting method. Marginal structural models give a nonparametric standardization using the total group (exposed and unexposed) as the standard. In epidemiologic analysis, it is also important to know the change in the average risk of the exposed (or the unexposed) subgroup produced by exposure, which corresponds to the exposed (or the unexposed) group as the standard. We propose modifications of the weights in the marginal structural models, which give the nonparametric estimation of standardized parameters. With the proposed weights, we can use the marginal structural models as a useful tool for the nonparametric multivariate standardization.

Antineoplastic Agents, Hormonal↗
PubMed2003

A global standard for anti-D immunoglobulin: international collaborative study to evaluate a candidate preparation.

BACKGROUND AND OBJECTIVES: The aim of the study was to evaluate a lyophilized anti-D immunoglobulin preparation to serve as a global standard for potency assays of anti-D immunoglobulin products. MATERIALS AND METHODS: The candidate global standard, 01/572, was calibrated against the World Health Organization (WHO) International Reference Preparation (IRP) for anti-D immunoglobulin, human (68/419), along with two reserve candidate reference preparations, in an international collaborative study involving 25 laboratories in 15 countries. The United States Food and Drug Administration (US-FDA) Center for Biologics Evaluation and Research (CBER) Standard for anti-D immunoglobulin, Lot 3, was included for comparison. Most laboratories (20/25) performed AutoAnalyser methodology, competitive enzyme-linked immunoassay (EIA) and/or flow cytometry. RESULTS: The overall mean potency of the candidate global standard, 01/572, was 284.5 international units (IU)/ampoule, with an interlaboratory variability, expressed as a percentage geometric coefficient of variation (% gcv), of 9.7. The mean potency of the US Standard was 859.4 IU/ml with an interlaboratory variability of 9.5% gcv, excluding an outlier. The mean potencies of the reserve preparations per ampoule/vial were 110.6 IU and 106.7 IU when calibrated against the IRP, and 112.2 IU and 106.6 IU when calibrated against 01/572, respectively, with interlaboratory % gcv values of 9.6-18.3 (excluding outliers). CONCLUSIONS: Preparation 01/572 proved more suitable for use as a global standard than the reserve candidate preparations and was established, with an assigned potency of 285 IU/ampoule, by the WHO as the 2nd International Standard for anti-D immunoglobulin; by FDA-CBER as the Standard for anti-D immunoglobulin, Lot 4; and by the European Directorate for the Quality of Medicines (EDQM) as the 1st Biological Reference Preparation for anti-D immunoglobulin.

Australia↗