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PubMed1983

Intercomparison of Nordic exposure secondary standards for soft roentgen rays.

An intercomparison of exposure secondary standards for soft roentgen rays in use in the Nordic countries is reported. One of the standards was used as a reference standard against which all the other standards were calibrated. The statistical uncertainty in the calibrations was estimated to be 0.8 per cent (at the 95% confidence level) and the maximum systematic uncertainty in the intercomparison was estimated to be 0.8 per cent. The observed differences, at most about one per cent, were not considered significant. It was concluded that for this type of chambers a period of about five years is acceptable between recalibrations against a primary standard unless stability checks indicate otherwise.

Calibration↗
PubMed1997

Standardization of marker assays--pyridinoline/deoxypyridinoline.

The hydroxypyridinium collagen crosslinks pyridinoline and deoxypyridinoline (Dpd) are released during the degradation of some mature collagens. Assays for the peptide forms of these crosslinks in blood and urine and for the free and total crosslinks in urine have been developed. Currently there is no internationally accepted reference standard for use in any of these assays. Recently the criteria and strategy for the preparation of a Dpd standard have been described. Using the UV molar absorptivity of 5160 L/mol/cm at 294 nm in 0.1 mol/L HCl and purity checked by NMR spectroscopy, mass spectrometry and elemental analysis sufficient quantities of this reference standard will have to be prepared. Protection from photolysis is essential to ensure stability of the reference preparation. This reference preparation will be suitable for calibration of immunoassays for free Dpd and for HPLC assays of free and total Dpd. The assays for peptide forms of the crosslinks have used standards prepared either by enzymatically digesting collagen or synthesis of oligopeptides. The problem of standardization of some of these peptide assays may be resolved if a reference preparation of digested bone collagen can be produced and appropriately characterised.

Amino Acids↗
PubMed1981

A U.S. reference for human immunoglobulin E.

The Committee on In Vitro Tests of the American Academy of Allergy has collected a large pool of human serum containing high titers of total IgE for the purpose of establishing a U.S. reference material. This pool is free from hepatitis B surface antigen. The serum pool has been subaliquoted, lyophilized and tested for total IgE content. The paper radioimmunosorbent test (PRIST) technique was used for this measurement. All laboratories used the same lot of reagents. The Second International Reference Preparation was used as the reference standard in each assay. Multiple replicates of the pooled sera was tested for total IgE content with one set of reagents by each of the 14 participating committee laboratories. The results for total IgE content (IU) of the vials were: mean of means, 899; median of means, 901; weighted mean, 898; with an overall coefficient of variation of 15.3%. This new IgE reference material is available to all laboratories for use as a primary reference standard from the Research Resources Branch, NIAID-NIH, Bethesda, MD 20205.

Humans↗
PubMed2003

Could the [14C]urea breath test be proposed as a 'gold standard' for detection of Helicobacter pylori infection ?

BACKGROUND: The urea breath test (UBT) with a microdose of [14C] is a non-invasive and simple method for the assessment of gastric infection by Helicobacter pylori. The aim of this study was to compare the [14C]UBT with invasive methods widely used for assessment of H. pylori gastric infection, including histology with hematoxylin-eosin staining, the gastric smear technique using Giemsa staining, and the biopsy urease test. MATERIAL/METHODS: We evaluated patients referred to our clinic for elective upper gastrointestinal endoscopy excluding those on antibiotics and/or bismuth during the previous 4 weeks, patients on H+ blockers or H2 antihistamines during the previous 7 days, pregnant women, and patients who had undergone gastric surgery or had bleeding disorders. Eighty-nine patients ranging in age from 18-75 years were included in the final study population, 61 women and 28 men (mean age: 43(15 years). RESULTS: When histology alone was considered as the reference standard, sensitivity for the [14 C]UBT was 94%, with a specificity of 37%; when the Giemsa technique, sensitivity was 95%, and specificity 35%; and when the biopsy urease test, sensitivity was 94% and specificity 45%. With two or more invasive techniques together considered as the reference standard, the [14C]UBT had a sensitivity of 95%, with a specificity of 44%. CONCLUSIONS: [14C]UBT is an objective and reproducible technique, capable of sampling the whole gastric mucosa. It shows high sensitivity, but low specificity, which could be explained by limited gastric sampling plus subjective interpretation in the invasive techniques that are currently used as gold standard.

Breath Tests↗
PubMed2003

A comparison of the International Standards Organisation reference method for the detection of coliforms and Escherichia coli in water with a defined substrate procedure.

AIMS: This study investigated the use of the International Standards Organisation (ISO) procedure for the comparison of microbiological methods. Using this procedure the ISO reference procedure for the detection of coliforms and Escherichia coli in water was compared with a defined substrate method (ColilertTM). METHODS AND RESULTS: A total of 20 laboratories from 13 European countries compared the use of Colilert/Quanti-TrayTM, a quantitative defined substrate test (DST) for the presence of coliforms and E. coli with the ISO reference procedure, which utilizes tergitol-TTC medium. Results of the study showed that DST detected significantly more coliforms and E. coli than did the reference procedure. In the case of E. coli the recoveries were also higher when using DST and the difference seen was statistically significant. The confirmation rate obtained when using the DST product suggested that no confirmation of wells positive for E. coli was necessary during routine use. CONCLUSIONS: Colilert is a suitable alternative to the ISO reference procedure for the detection of coliforms and E. coli in water. The methods used during the comparison study indicated that confirmation of all colonies/positive wells led to the most accurate information and it is recommended that for future comparison studies this should become standard practice. Confirmation of a small proportion of colonies led to misleading conclusions and should be avoided when comparing microbiological methods. SIGNIFICANCE AND IMPACT OF STUDY: It has been demonstrated that the ISO reference procedure fails to detect a significant proportion of coliforms and E. coli in drinking water. Colilert/QuantiTrayTM is a more suitable alternative.

Bacteriological Techniques↗
PubMedDate not supplied

Determination of ultratrace levels of lead in infant formula by isotope dilution inductively coupled plasma mass spectrometry.

A simple method was developed for the accurate and precise determination of low- and sub-ppb (ng/g) concentrations of lead in infant formula by isotope dilution inductively coupled plasma mass spectrometry using ultrasonic nebulization. After addition of a known amount of 207Pb, samples were microwave digested and the ratio 207Pb/208Pb was measured in the digests. Agreement with certified values for lead in milk powder standard reference materials was good, and isotope dilution analysis using 206Pb yielded identical results for the standard reference materials. Lead concentrations determined for several infant nutritional products were verified by an independent method. Typically, relative standard deviations of < 4% were obtained with this method for lead concentrations above 2 ppb. The recovery of 2 ng of lead from an aqueous standard carried through the microwave digestion was 104 +/- 4%. Infant formula (containing 0.6 ppb lead) to which 0.4 ng of natural-abundance lead had been added, to simulate a formula containing 0.9 ppb lead, was analyzed by isotope dilution, and the result was 96 +/- 18% of the theoretical value. Thus, differences of 0.3 ppb lead could be clearly distinguished, and the detection limit was estimated to be 0.1 ng lead per gram of infant formula. The keys to accuracy for this method are minimizing contamination and accurately determining the concentration of lead in the isotopically enriched standard.

Food Contamination↗
PubMed2005

Development and application of a quantitative RT-PCR potency assay for a pentavalent rotavirus vaccine (RotaTeq).

A sensitive and reproducible method to determine the in vitro infectious potency of a pentavalent reassortant rotavirus vaccine (RotaTeq) has been developed as an alternative to classical potency assays. Potency was determined based on cell-based viral replication followed by quantitative reverse-transcription polymerase chain reaction (RT-QPCR) analysis. In the assay, confluent Vero cell monolayers in 96-well plates were inoculated with serial dilutions of test samples, a pentavalent reassortant rotavirus reference standard and assay controls, followed by incubation for 24h. The cells were lysed with a Triton X-100 solution and the lysates assayed by RT-QPCR to quantitate viral nucleic acid produced during replication. The RT-QPCR utilizes primer/probe sets specific to each virus reassortant and the potencies of each sample were determined relative to the reference standard. This assay, hereafter referred to as the Multivalent QPCR-Based Potency Assay (M-QPA), permits the specific quantitation of each individual reassortant virus in the presence of the other four reassortant viruses. In addition, the assay was demonstrated to be concordant with a traditional method (plaque assay) for the quantitation of infectious virus particles. It is anticipated that assays of this type will become a valuable tool in the assignment of potency values and in the monitoring of stability of live virus vaccines.

Animals↗
PubMed1999

The concept of abnormality in medical genetics.

This paper explores usage of the concept of abnormality in medical genetics and proposes directives for more careful usage of this concept. The conceptual difficulties are first explored, then a model is developed to assess actual usage, followed by analysis of a sample of genetic textbooks and genetics literature. It appears that fact and valuation are often intermingled, that reference standards used to define 'genetic abnormalities' are often not clear and that the concept of abnormality is often used independent of the degree of certainty with which the altered genetype develops into a (seriously) harmful phenotype. On the basis of these findings it is argued that more restraint and more careful use of the concept of genetic abnormality of medical genetics is appropriate as well as more agreement on the use of reference standards.

Congenital Abnormalities↗
PubMed1996

Measuring capacity to complete an advance directive.

OBJECTIVE: To validate reference standards for the assessment of capacity to complete an advance directive and to develop and test three simple screening instruments. METHODS: We administered five measures of capacity to 96 older subjects from nursing homes, retirement homes, and homes for the aged. The measures included two reference standard evaluations: an assessment by a specially trained nurse in collaboration with a multidisciplinary team (Competency Clinic assessment) and geriatrician assessment using a decisional aid. Three screening instruments were also included: a Generic Instrument designed for any advance directive, a Specific Instrument designed for the "Let Me Decide" advance directive, and the Standardized Mini-Mental Status Examination (SMMSE). The screening instruments and the geriatrician's assessment were administered twice to half of the respondents to determine interrater agreement. RESULTS: The chance-corrected agreement for the assessment by two geriatricians was 0.78, and for agreement between the geriatricians and Competency Clinic assessments it was 0.82. Agreement for the Generic and Specific screening instrument assessments by two observers was 0.77 and 0.90, respectively. The areas under the Receiver Operating Characteristic curve relating the results of the three screening instruments to the Competency Clinic assessment were 0.82 for the Generic Instrument, 0.90 for the Specific Instrument, and 0.94 for the SMMSE; chance is an unlikely explanation for the difference between these three values (P < or = .01). CONCLUSIONS: Using rigorous methods, health workers can make reproducible and valid assessments of capacity to complete an advance directive. The SMMSE accurately differentiates people who can learn about and ultimately complete advance directives from those who cannot.

Advance Directives↗
PubMed2003

Establishment of European Pharmacopoeia BRP batch 2 for inactivated poliomyelitis vaccine for in vitro D antigen assay.

A collaborative study was initiated by the European Directorate for the Quality of Medicines (EDQM) to assign a potency value for the candidate Ph Eur BRP batch 2 against the 2nd International Standard (IS) in order to replace the dwindling stocks of Ph Eur BRP batch 1. The candidate material is a concentrated trivalent bulk (Type 1 (Mahoney), Type 2 (MEF1) and Type 3 (SAUKETT)) from a commercially available IPV vaccine. Nine laboratories participated in the collaborative study. Eight laboratories reported results. Participants performed in-house ELISA assays on the candidate BRP, the 2nd International Standard (IS) and the current BRP (BRP batch 1). An additional sample was included to acquire information on the correlation between the in vitro and in vivo assays based on comparison with a previous study. Results of that comparison are included as an annex. Potency estimates were satisfactory in terms of repeatability and reproducibility, however the estimates for the 2nd IS were significantly lower than those for Ph Eur BRP batch 1. These two reference standards are derived from the same material and were originally assigned the same potency value after a joint study run by EDQM and the WHO in 1994. A reconciliation study was therefore designed to determine if the IS stored at NIBSC and the IS which had been sent from NIBSC to EDQM for use in the initial study were equivalent. 3 of the laboratories from the initial study participated. Results revealed no significant difference between the 2nd IS stocks stored in the two different locations at NIBSC nor between BRP batch 1 and the standards stored at NIBSC for types 1 and 2. For type 3 the 2nd IS standards stored at NIBSC are 13 % less potent than the Ph Eur BRP batch 1. The 2nd IS which had been shipped from NIBSC to EDQM was significantly less potent than BRP batch 1 and the 2nd ISs stored at NIBSC for all three types, confirming the observation of the initial study. Possible explanations for this apparent loss of potency of the 2nd IS used in the study are under investigation. Since Ph Eur BRP batch 1 and the 2nd IS in stock at NIBSC appear no more different than when their original potency assignment was made at their establishment, and since the 2nd IS standard used in the initial part of this study was compromised, a consensus potency value for the candidate BRP was determined using Ph Eur BRP batch 1 as the reference standard. The candidate material was therefore assigned a potency of 320-67-282 D Antigen units/ml (IU) for types 1, 2 and 3 respectively. A stability monitoring program will be initiated. The candidate material was adopted by the European Pharmacopoeia Commission at its session in March 2003 as European Pharmacopoeia IPV vaccine BRP batch 2 for D Ag in vitro assay.

Animals↗
PubMed1999

Antioxidative activity of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid.

The (-)-(1S, 3S) isomer of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid was synthesised by Pictet-Spengler condensation of tryptophan with acetaldehyde. It was evaluated for its antioxidative activity in the linoleic acid autooxidation system by the ferric thiocynate method. Butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), and alpha-tocopherol were used as the reference standards. The compound showed moderate antioxidative activity and also synergistic effect with the reference standards. The synergistic effect was in the increasing order of BHT, alpha-tocopherol and BHA. The synergistic effect was higher at higher concentrations studied.

Antioxidants↗
PubMed2003

Contributions of symptoms, signs, erythrocyte sedimentation rate, and C-reactive protein to a diagnosis of pneumonia in acute lower respiratory tract infection.

BACKGROUND: Diagnostic tests enabling general practitioners (GPs) to differentiate rapidly between pneumonia and other lower respiratory tract infections (LRTIs) are needed to prevent increase of bacterial resistance by unjustified antibiotic prescribing. AIMS: To assess the diagnostic value of symptoms, signs, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) for pneumonia; to derive a prediction rule for the presence of pneumonia; and to identify a low-risk group of patients who do not require antibiotic treatment. DESIGN OF STUDY: Cross-sectional. SETTING: Fifteen GP surgeries in the southern part of The Netherlands. METHOD: Twenty-five GPs recorded clinical information and diagnosis in 246 adult patients presenting with LRTI. Venous blood samples for CRP and ESR were taken and chest radiographs (reference standard) were made. Odds ratios, describing the relationships between discrete diagnostic variables and reference standard (pneumonia or no pneumonia) were calculated. Receiver operating characteristic analysis of ESR, CRP, and final models for pneumonia was performed. Prediction rules for pneumonia were derived from multiple logistic regression analysis. RESULTS: Dry cough, diarrhoea, and a recorded temperature of > or = 38 degrees C were independent and statistically significant predictors of pneumonia, whereas abnormal pulmonary auscultation and clinical diagnosis of pneumonia by the GPs were not. ESR and CRP had higher diagnostic odds ratios than any of the symptoms and signs. Adding CRP to the final 'symptoms and signs' model significantly increased the probability of correct diagnosis. Applying a prediction rule for low-risk patients, including a CRP of < 20, 80 of the 193 antibiotic prescriptions could have been prevented with a maximum risk of 2.5% of missing a pneumonia case. CONCLUSION: Most symptoms and signs traditionally associated with pneumonia are not predictive of pneumonia in general practice. The prediction rule for low-risk patients presented here, including a CRP of < 20, can considerably reduce unjustified antibiotic prescribing.

Adolescent↗
PubMed2006

[Value of intradermal skin test and serum sIgE detection in diagnosing artemisia pollinosis].

OBJECTIVE: To evaluate the value of intradermal skin test (IDT) and serum sIgE detection in diagnosing Artemisia sensitivity in Chinese patients with autumnal hay fever. METHODS: 1150 patients with autumnal rhinitis or asthma, 504 males and 646 females, aged 5 approximately 77, were evaluated by experienced physicians, then underwent IDT by using 20 kinds of aeroallergen extracts. The concentrations of Artemisia and Ragweed extracts employed in skin test were 1:1000 (W/V) and the concentrations of other aeroallergens were all 1:100 (W/V). Then all patients underwent detection of Artemisia sIgE. Diagnostic standards were established based on the results of IDT and sIgE results respectively. A reference standard was established according to the typical history, symptoms, and an wheal with a diameter >or= 5mm and a sIgE level >or= 0.35 kU(A)/L, an wheal with the diameter >or= 10 mm alone; or a sIgE level >or= 0.70 kUa/L alone. RESULTS: When using the reference standard as criteria, using IDT had better sensitivity (96.2%), specificity (74.2%), positive predictive value (+PV, 93.5%), negative predictive value (-PV, 85.7%), and efficiency (91.6%) than using sIgE >or= 0.35 kUa/L alone as the criteria of IDT; sIgE detection had better sensitivity (97.6%), specificity (94.9%), +PV (98.7%), -PV (91.1%), and efficiency (97.0%) than using wheal diameter >or= 5 mm alone as the criteria of sIgE detection. The false positive rate of IDT and sIgE detection decreased from 35% and 22.7% to 25.6% and 5.1% respectively when using the wheal diameter >or= 10 mm or sIgE >or= 0.70 kUa/L as a positive criteria. CONCLUSION: IDT and sIgE detection are correlated with each other well in diagnosing Artemisia pollinosis, both of them have the possibility of being false positive, but IDT has higher false positive rate than sIgE detection. The false positive rates of IDT and sIgE detection can be decreased by increasing the positive criteria to higher grading reaction.

Adolescent↗
PubMedDate not supplied

The suitability of an in situ perfusion model for permeability determinations: utility for BCS class I biowaiver requests.

The FDA has published recommendations for sponsors who wish to request a waiver of in vivo bioavailability (BA) or bioequivalence (BE) studies for immediate release (IR) solid oral dosage forms based on the Biopharmaceutics Classification System (BCS). Biowaivers can be requested for IR formulations in which the active ingredient is shown to be a BCS class I drug: that is, a drug showing high permeability and high solubility over a pH range of 1-7.5. For permeability determinations, a variety of experimental methods can be used, such as the rat in situ single pass perfusion or Caco-2 cell culture models, once the suitability of the particular method is established. Following the recommended procedure for assessing the suitability of permeability determinations, we determined the permeability of 20 test drugs using the in situ single pass perfusion model in rats. The test compounds were coperfused through jejunal intestinal segments with an internal permeability reference standard (metoprolol) over a 90 min time period. Sample analysis was performed by HPLC, and the ratio of the effective permeability, Peff (cm/s), of test compound to that of metoprolol was determined. To address the question of test drug permeabilities that approach that of the internal standard, we propose that a statistical analysis such as the "0.8-1.25 rule" used for in vivo or in vitro bioequivalence studies provide guidance for permeability classification using the in situ single pass perfusion model. We developed a method using the 90% confidence interval of the permeability ratio of the test to internal reference standard in order to differentiate between high and low permeability compounds. This analysis allowed for the proper permeability classification of all of the test compounds and suggests a robust means for assessing drug permeability classification.

Animals↗
PubMed1999

Standardisation of DNA quantitation by image analysis: quality control of instrumentation.

BACKGROUND: DNA image analysis is frequently performed in clinical practice as a prognostic tool and to improve diagnosis. The precision of prognosis and diagnosis depends on the accuracy of analysis and particularly on the quality of image analysis systems. It has been reported that image analysis systems used for DNA quantification differ widely in their characteristics (Thunissen et al.: Cytometry 27: 21-25, 1997). This induces inter-laboratory variations when the same sample is analysed in different laboratories. In microscopic image analysis, the principal instrumentation errors arise from the optical and electronic parts of systems. They bring about problems of instability, non-linearity, and shading and glare phenomena. METHODS: The aim of this study is to establish tools and standardised quality control procedures for microscopic image analysis systems. Specific reference standard slides have been developed to control instability, non-linearity, shading and glare phenomena and segmentation efficiency. RESULTS: Some systems have been controlled with these tools and these quality control procedures. Interpretation criteria and accuracy limits of these quality control procedures are proposed according to the conclusions of a European project called PRESS project (Prototype Reference Standard Slide). Beyond these limits, tested image analysis systems are not qualified to realise precise DNA analysis. CONCLUSIONS: The different procedures presented in this work determine if an image analysis system is qualified to deliver sufficiently precise DNA measurements for cancer case analysis. If the controlled systems are beyond the defined limits, some recommendations are given to find a solution to the problem.

DNA, Neoplasm↗
PubMed2005

Do we measure bilirubin correctly anno 2005?

We observed 30% discrepancy between liquid chemistry and dry chemistry analysers for the determination of total bilirubin in human adult serum samples, which were consistent with a 20% overestimation and 10% underestimation relative to a Jendrassik-Grof reference method, respectively. In contrast, standard reference material SRM916, which was recently recommended as being the most suitable material for attaining interlaboratory agreement, shows very good agreement on both types of analysers, as well as close to 100% recovery with respect to the reference method. We show that the liquid vs. dry bilirubin discrepancies seem to originate in the presence of either conjugated or delta-bilirubin. Our observations make it clear that good interlaboratory (or inter-analyser) agreement between bilirubin reference materials does not guarantee the same for bilirubin concentrations in human serum samples.

Adult↗
PubMed1988

Use of a predictor for total body potassium content: application to nutrition and hypertension.

Total body potassium (TBK), measured at different institutions, has no reference standard for comparison. A useful reference formula, however, based on body size and age, has been derived at the Brookhaven National Laboratory. This formula was used to help calibrate a simple whole body counter for measuring total potassium and applied to nutrition and hypertension studies. A sodium iodide detector was used for counting gamma rays emitted by potassium-40 to estimate TBK. The mean ratio (+/- S.D.) of adjusted TBK measurements to predicted values was 1.002 +/- 0.047. The ratio of lean body mass estimated by the TBK measurement to that derived from skin fold thickness was 1.069 +/- 0.056. In hypertensives on low dose thiazide, the ratio of TBK measurements to predicted values was 0.994 +/- 0.052. Thus, our TBK measurements were adjusted in close agreement with a predictor formula, provided higher estimates of lean body mass than did skin fold thickness, and showed no change in thiazide treated hypertensives.

Adult↗
PubMed1994

Rapid automated enzyme immunoassay of serum amyloid A.

Serum amyloid A (SAA), a sensitive acute-phase protein, is the precursor of AA fibrils in reactive amyloidosis. However, SAA is poorly immunogenic, and development and standardization of immunoassays of this protein have been difficult. We established an automated polyclonal/monoclonal microparticle capture enzyme immunoassay, standardized with the World Health Organization prospective reference standard for SAA. A stabilized concentrate of SAA was used for controls and calibrators. The assay range was 1-750 mg/L with CVs < 7% throughout. Plasma and serum gave identical results and no interferences were observed. Linear regression against radial immunodiffusion assay gave a slope of 1.04 (95% confidence interval 0.99-1.10), intercept of -9 mg/L (95% confidence interval -14-3), and residual SD (SEE) of 20 for samples containing < or = 200 mg/L (n = 173). In 105 apparently healthy adults the mean (SD) SAA concentration was 3.7 (3.6) mg/L, the median was 3.0 mg/L, and the range, 0.7-26.4 mg/L. In clinical acute-phase sera, values up to 2200 mg/L were seen. This method will facilitate measurement and investigation of SAA in clinical practice generally and in AA amyloidosis.

Acute-Phase Reaction↗