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PubMed1983

The stability of tissue plasminogen activator (t-PA).

Since tissue-type plasminogen activator (t-PA) derived from tissue culture and recombinant DNA procedures has been proposed for use in thrombolytic therapy in man, it is essential that the t-PA molecule should display reasonable stability in a lyophilised state to facilitate its usefulness. In this study, four laboratories compared the potencies of three preparations of t-PA following storage at 4 degrees, 20 degrees, 37 degrees and 45 degrees C, using each t-PA stored at -20 degrees C as a reference (100% activity) in each case. A pig heart extract of t-PA was the most stable, losing no activity when stored for 30 days at 37 degrees C, while two melanoma cell tissue culture extracts varied in their storage behaviour. One was quite stable at 37 degrees C (losing about 3% of its activity) while the other lost about 16%. Thus both the pig heart t-PA and one t-PA from melanoma cell culture proved suitable for the further development of reference standards for t-PA activity.

Animals↗
PubMed1996

Study design for the evaluation of diagnostic tests.

Diagnostic tests, like therapeutic procedures, require proper analysis prior to incorporation into clinical practice. In studying diagnostic tests, an evaluation should be made of the reproducibility, accuracy, variation among those without the disease, and variation among those with the disease. Both diseased and disease-free states should be identified using a gold standard, if available. Three main guidelines can be used in evaluating and applying the results of diagnostic tests: validity of the study, expression of the results, and assessment of the generalizability of the results. Validity requires an independent, blind comparison with a reference standard. Methodology should be fully explained. Results should include sensitivity, specificity, and a receiver operating characteristic plot. Several categories of results should be provided in the form of likelihood ratios. Management decisions can be made on the basis of the posttest probability of disease after including both the pretest probability and the likelihood ratio in the calculation.

Data Interpretation, Statistical↗
PubMedDate not supplied

Identification of hydrolyzed inulin syrup and high-fructose corn syrup in apple juice by capillary gas chromatography: PVM 4:1999.

A peer-verified, gas chromatographic (GC) method is presented for the identification of hydrolyzed inulin syrup (HIS) and high-fructose corn syrup (HFCS) in apple juice. The procedure involves determining the Brix value of the apple juice or apple juice concentrate and preparing a dilution of the test sample to 5.5 degrees Brix. A 100 microL aliquot of the 5.5 degrees Brix test solution is then freeze-dried in a GC autosampler vial. The sugars in the freeze-dried residue are converted to trimethylsilyl derivatives, by the addition of an appropriate silylation reagent, and the vial is heated at 75 degrees C for 30 min. After derivatization, the solution is introduced into a gas chromatograph where the analytes are separated on a 30 m, 0.25 mm id DB-5 column. The method can use hydrogen, helium, or nitrogen as the carrier gas. The analytes and marker compounds are measured by use of a flame ionization detecone of the 2 syrups at 2 levels. Dilution was ascertained by the presence of retrograde sugar markers found in the 2 sugar syrups. All 3 laboratories involved in the study were able to identify the correct diluent in the blind, randomly coded, apple juice test portions. The levels of dilution in the test portions were 0, 6.9% (HIS), 16.0% (HIS), 8.1% (HFCS), and 17.0% (HFCS). No false positive results were reported. Quantitative conclusions can be drawn when the same syrup is used for dilution and as a reference standard.

Beverages↗
PubMed1985

Anthropometric cut-off points for diagnosis of malnutrition: are they applicable in developing countries? A study in healthy African adults, North-East Nigeria.

Anthropometric evaluations of the upper limb were performed on 614 healthy African adults who were employees of two hospitals in Maiduguri, North-East Nigeria. Measurements were related to reference standards of Jelliffe (1966) and to centiles derived from the United States Health and Nutrition examination survey of 1971 to 1974. A large proportion of subjects, particularly men, fell below the 5th centile and 90 per cent of the Jelliffe reference. These cutoff points, which are often taken to indicate nutritional depletion in developed countries, cannot be used as similar nutritional indicators in this part of Africa.

Adolescent↗
PubMed2006

Selective manipulation of steroid hydroxyl groups with boronate esters: Efficient access to antigenic C-3 linked steroid-protein conjugates and steroid sulfate standards for drug detection.

The temporary protection of 17alpha-alkyl-5alpha-androstane-3beta,16beta,17beta triols as boronate esters is an efficient method for their regioselective functionalisation. This has been applied to the synthesis of protein-steroid conjugates 7-10 suitable for the development of immunoassays targeting classes of steroids banned from competition in Australian horse racing and other sports. The synthesis of steroids sulfate conjugates 42 and 44 for use as reference standards is also reported.

Antigens↗
PubMed1999

Waist circumference values in Spanish children--gender related differences.

OBJECTIVE: To obtain reference values of the waist circumference in Spanish children, and to investigate their dependence on age and gender. DESIGN: Cross-sectional study. SETTING: General school-age population. SUBJECTS: A representative sample of the schools in Zaragoza, Spain, was drawn from seven schools. The population selected comprised 1728 children with ages ranging from 6.0-14.9y. Of the original sample, 368 children (21.29%) were excluded because of chronic diseases or refusal. Finally, 1360 children and adolescents: 701 boys and 659 girls, were studied. INTERVENTIONS: Waist and hip circumferences were measured with an unelastic tape. RESULTS: Waist circumference tended to be higher in males than in females and this difference was significant after 11.5y. In general, hip circumference was higher in females than in males (statistically significant differences at 7.5, 10.5, 12.5 and 13.5 y). In general, percentile values of waist circumference were higher in males than in females, especially after 12.5 y. Difference between males and females on percentile 95 at 14.5 y was 7.6 cm. Hip was greater than waist in both sexes, and the two curves run nearly parallel in males. In females, while hip enlarges continuously, waist shows the reverse tendency between 11.5 and 14.5 y. CONCLUSIONS: Waist circumference showed higher values in boys than in girls, especially after 11.5 y, and waist values increase with age both in males and females. These findings justify the use of age and gender specific reference standards.

Abdomen↗
PubMed2006

Synthesis of fluorinated polybrominated diphenyl ethers (F-PBDEs) as internal standards for environmental analysis.

Polybrominated diphenyl ethers (PBDEs) have become widely distributed as environmental contaminants due to their wide-spread use as flame retardants. Their structural similarity to other halogenated organic pollutants, for example polychlorinated biphenyls (PCBs), has led to speculation that they may have similar toxicological properties and effects. Recent focus on PBDEs as possible priority pollutants has also led to an increasing need for reference standards of PBDEs for toxicological studies and for environmental analysis. In this work we synthesized a series of fluorinated PBDEs (F-PBDEs) which can be used as possible internal standards, as an alternative to high-cost alternatives, such as the (13)C-labelled analogues. F-PBDEs have been synthesized by using different coupling reactions and by bromination of fluorinated starting materials.

Environmental Monitoring↗
PubMed2001

Determination of 2,4-dichlorophenoxyacetic acid (2,4-D) in human urine with mass selective detection.

Method development and validation studies have been completed on an assay that will allow the determination of 2,4-dichlorophenoxyacetic acid (2,4-D) in human urine. The accurate determination of 2,4-D in urine is an important factor in monitoring worker and population exposure. These studies successfully validated a method for the detection of 2,4-D in urine at a limit of quantitation (LOQ) of 5.00 ppb (parts per billion) using gas chromatography with mass selective detection (GC/MSD). The first study involved the determination of 2,4-D in control human urine and urine samples fortified with 2,4-D. Due to chromatographic interference, a second study was conducted using 14C-2,4-D to verify the recoverability of 2,4-D from human urine at low levels using the GC/MSD method. The second study supports the results of the original data. The 2,4-D was extracted from human urine using a procedure involving hydrolysis using potassium hydroxide, followed by a liquid-liquid extraction into methylene chloride. The extracted samples were derivatized with diazomethane. The methylated fraction was analyzed by GC/MSD. Quantitation was made by comparison to methylated reference standards of 2,4-D. Aliquots fortified at 5-, 50-, and 500-ppb levels were analyzed. The overall mean recovery for all fortified samples was 90.3% with a relative standard deviation of 14.31%.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1990

Validity of tissue paste standards for quantitative whole-body autoradiography using short-lived radionuclides.

A method of preparing radioactive standards for quantitative whole-body autoradiography (WBARG) using short-lived radionuclides is described and evaluated. Radioactive standards were prepared from bovine brain paste which was mixed with serial dilutions of the radionuclide being studied. Homogeneous distribution of the radionuclide in the brain paste was verified by direct counting and autoradiographic techniques. In addition, there was good agreement between the amounts of radioactivity obtained from quantitative WBARG and tissue counting in all of the major tissues sampled. Therefore, this method is effective for quantitative analysis of WBARG using short-lived radionuclides, for which permanent reference standards are unavailable.

Animals↗
PubMed2006

Spine bone densitometry in asthmatic children treated with high dose corticosteroids: correcting for racial discrepancies.

PURPOSE: Our hypothesis is that the use of standards based on Caucasian children will under-estimate the incidence of abnormal bone density in African American children. MATERIALS AND METHODS: Eighty-two African American and 80 Caucasian asthmatic children classified as high-dose inhaled corticosteroid users comprised the study population. Bone mineral density measurements were compared to reference standards, based on Caucasians, to calculate Z-values. Regression analysis was used to compare Z-values derived from the race-specific and Caucasian standards for 32 African American children. The derived regression analysis equation was then applied to the entire African American population to determine the incidence of abnormal bone density. RESULTS: The asthmatic Caucasian mean spine bone density was significantly less than the normal standards (p < .001), but the African American mean spine bone density was not, despite the high-dose steroid use. Using the Caucasian standards, Caucasians were significantly more likely to have abnormal bone density detected (p < 0.015). Regression analysis of the 32 children with available race specific standards resulted in the following equation: Z African American= Z Caucasian-0.86. The number of African Americans with abnormal bone density detected using the regression equation was not significantly different than the Caucasian children (p > 0.12). CONCLUSIONS: Asthmatic African Americans treated with high-dose inhaled corticosteroids had denser bones than Caucasians. Caucasian standards can be adjusted using a regression equation.

Absorptiometry, Photon↗
PubMed1993

Radiochemical neutron activation analysis of Fe, Co, Zn, Sb and Se in biomedical and environmental samples.

A radiochemical neutron activation method has been developed for the simultaneous determination of Fe, Co, Zn, Sb and Se levels in cancerous breast tissue, milk samples and fugitive cement dust particulates. Various Standard Reference Materials from NIST, USA (Bovine Liver 1577a, Milk Powder 1549, Coal Fly Ash 1633a and Urban Particulate Matter 1648), IAEA Vienna (Animal Muscle H-4, Milk powder A-11 and Soil-5) and NIES Japan (Pond Sediment) were also analysed for quality control. Samples together with standards were irradiated at a thermal neutron fluence of 10(13) ncm-2s-1 for 2 weeks. After dissolution/fusion together with carriers, the Fe was first separated by extracting with diethyl ether followed by extraction with cupferron in chloroform. From the aqueous phase Co and Zn were extracted using alpha-nitroso-beta-naphthol in chloroform and 2-thenoyltrifluoroacetone in isobutylmethyl ketone, respectively. From another aliquot, Se was first complexed with o-phenylenediamine and extracted in benzene. Later Sb was extracted using KI and 4-(2-pyridylazo)-resorcinol (PAR) in benzene. The method yields reasonably accurate data for monitoring of trace elements in biomedical and environmental specimens.

Animals↗
PubMed1998

Do different heparin brands influence activated clotting times?

A change in brand suppliers of heparin at our institution resulted in a number of anecdotal reports of possible differences in potency. Both products are marketed as heparin sodium extracted from porcine intestinal mucosa. Heparin Leo is 1000 international units (British Pharmacopeia) per ml. while Hepalean is 10,000 United States Pharmacopeia (U.S.P) units per ml. Perfusion records were retrospectively reviewed for one month periods when Heparin Leo (n = 52) or Hepalean (n = 61) were used to provide anticoagulation therapy for cardiopulmonary bypass. Heparin Leo was found to be less clinically potent than Hepalean. While increasing the initial loading dose of Heparin Leo by 5% (378 vs 398 units/kg-1), the initial post load activated clotting time (ACT) was 17% lower (556 vs 666 seconds). Heparin units required per kilogram per minute of cardiopulmonary bypass were 23% higher for Heparin Leo. Additionally 8 of 52 Heparin Leo patients did not achieve an initial post load ACT of greater than 400 secs while this occurred in 2 of 61 patients treated with Hepalean. These results were statistically significant. British Pharmacopeia and United States Pharmacopeia heparin reference standards differences are insufficient to explain the discrepancies observed in this study.

Animals↗
PubMed1989

Quality control procedures for monitoring whole blood and plasma trace metal levels by atomic absorption spectrophotometry.

Well co-ordinated quality control procedures are required to insure that trace metal results determined at ppb (micrograms kg-1 or micrograms l-1) levels by atomic absorption spectrophotometry are reliable. Control materials can be prepared "in-house" provided they are calibrated against standard reference materials (SRM). A mean +/- SD data base should be determined for each quality control material with daily results plotted on Levey-Jennings charts. Westgard's multi-rule quality control scheme is recommended for assessing analytical performance. Additional information may be obtained by using cumulative sum (cusum) charts to detect analytical drift from the mean, and standard deviation index or 'z-score' plot to show analytical bias. Proficiency or quality assurance programs should be used to supplement internal quality verification of analytical performance.

Humans↗
PubMedDate not supplied

Industrial hygiene sampling and applications to ambient silica monitoring.

Interest in ambient exposures to silica has prompted an evaluation of the applicability of the industrial hygiene sampling and analysis experience. Exposure to excessive levels of silica in the workplace has long been recognized as a risk factor for the development of a variety of disabling and sometimes fatal lung diseases. Initial efforts to control occupational exposure to dust were based on reducing exposures as measured by particle-counting techniques. Because silicosis, the disease resulting from exposure to silica, occurs in the lower airways, which can be reached only by small "respirable dust" particles, size selective sampling procedures were introduced for dust monitoring. The analysis of silica in collected dust samples also has undergone development. Initial methods used involved acid digestion of soluble silicates, with subsequent chemical analysis of the insoluble "free silica" fraction. Current methodology relies on the use of X-ray diffraction and infrared technologies to quantify these materials. However, these methods are sensitive to the particle size distribution of the samples. Standard reference materials (SRMs) have been developed for use with respirable size dust samples. Ambient particulate matter is now measured using the U.S. Environmental Protection Agency sampling methods for particulate matter < or = 10 microns, which approximate the collection efficiency for thoracic fraction samplers. Because the existing calibration SRMs were produced for the measurement of occupational crystalline silica, the need to develop appropriate standards and methods for ambient silica measurements should be evaluated.

Air Pollutants, Occupational↗
PubMed1993

Standardisation and validation of enzyme-linked immunosorbent assay techniques for the detection of antibody in infectious disease diagnosis.

Enzyme-linked immunosorbent assay (ELISA) techniques for the detection of antibodies are now widely used throughout the world for the diagnosis of infectious diseases in veterinary medicine. Although many laboratories have independently developed ELISA techniques for their own purposes, little progress has been made with respect to the international standardisation and validation of these techniques. This lack of international conformity is of major concern to organisations such as the Office International des Epizooties (OIE), the United Nations Food and Agriculture Organisation (FAO), the World Health Organisation (WHO) and the International Atomic Energy Agency (IAEA) which are involved in the establishment of international guidelines and programmes for the control, surveillance and/or eradication of infectious diseases. In this regard, a Joint FAO/IAEA Meeting of Consultants was convened in Vienna in January 1992 to review aspects of ELISA data expression, primary reference standards, quality assurance and diagnostic validation. Based on the consensus derived from this meeting, the authors describe procedures which are recommended as a platform on which to build definitive guidelines for international standardisation of ELISA protocols and reagents, in cooperation with the OIE and the OIE Reference Laboratories.

Animals↗
PubMed1998

Bias in discrepant analysis: when two wrongs don't make a right.

Imperfect reference standards (alloyed standards) often hinder evaluation of new diagnostic tests. Discrepant analysis, a two-stage modification of the standard evaluation of diagnostic tests, has been used to circumvent this problem. In discrepant analysis, additional testing is performed to resolve discrepant results of the new diagnostic test and the alloyed standard. This article demonstrates algebraically that sensitivity and specificity will be overestimated by discrepant analysis, even when a perfect gold standard is used to resolve the discrepant results. The magnitude of the bias depends on the true sensitivity and specificity of the new test and initial alloyed standard, the prevalence of disease in the study population, and the proportion of concordant errors between the two tests. The article also demonstrates substantial bias associated with the use of alloyed standard tests in both stages of discrepant analysis. This procedure should not be used routinely for evaluation of diagnostic tests.

Bias↗
PubMed2006

A review of WHO International Standards for botulinum antitoxins.

Clostridium botulinum produces the most potent known toxins, with seven distinct serotypes currently defined (A-G). These toxins can cause a life threatening systemic toxicity whether through natural causes such as food poisoning, infant botulism, wound botulism, or through use as bio-terror agents (e.g. inhalational botulism). It was realised early on that standard reference botulinum antitoxins were required to reduce the variation between assays and ensure a consistent potency of therapeutic antitoxins and vaccines, and to define the serotype. This led to the International Unit being defined by the World Health Organisation (WHO) in the 1960s with the establishment of the first International Standards (IS) for serotypes A-F. Since then botulinum antitoxin ISs have been used world wide as the 'yard stick' to measure the neutralising potency of antitoxins. These primary WHO ISs are used to calibrate in house working reagents that are more extensively utilised. A definition of the International Unit for serotype G antitoxin has yet to be defined or accepted by the WHO and urgently needs addressing. However, before September 11th 2001 there was very little interest in botulinum antitoxin IS and as a result stocks of most of the original preparations are now completely exhausted or depleted and replacements long overdue. We have reviewed the extensive history and availability of the primary WHO ISs and interim materials. All type A and B antitoxin materials were recently assayed and their relative activities confirmed against the original IS preparations. The recent increase in demand for these materials has further exacerbated the shortage. We describe here the production and characterization of stable freeze dried potential candidate replacements along with a new prospective first IS for type G antitoxin. Available toxin A reference preparations are also briefly reviewed.

Animals↗
PubMed1985

Carotid ultrasonography--the new "gold standard". Surgical and angiographic correlation.

Atherosclerotic plaques and high grade stenosis in the carotid circulation are responsible for symptoms of cerebral and retinal ischemia. Identification of these lesions by angiography has been the "gold standard" for which the decision of endarterectomy depended. The recent introduction of high resolution carotid ultrasonography has allowed us to compare thirty-seven surgical specimens with the results of preoperative screening with angiography. UCI had a 97% correlation whereas angiography was accurate only 70%. More importantly there were ten negative angiograms in patients with clinically active ulcerative plaque disease. If surgery were based solely on the angiographic appearance of ulcerative plaques or high grade stenosis, then less than half of the patients have received the correct treatment. UCI deserves to be considered the new reference standard.

Angiography↗