SEARCH · Search PubMed

Results for “Reference Standards”

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

SourceResearch connectionFrom yearThrough year

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

At least 1,783 records · Page 99Linked to original sources

PubMed1988

Quantitative X-ray diffraction analysis of urinary calculi by use of the internal-standard method and reference intensity ratios.

The internal-standard method and the powder diffractometer have been applied here to the quantitative determination of urinary stone constituents by x-ray diffraction (XRD). Reference intensity ratios determined for six stone substances were used in the reduction of intensity data. Constituent concentrations calculated for 21 stones were compared with values obtained from an element-sensitive technique. We conclude that XRD analysis alone cannot be regarded as a routine technique for the quantitative characterization of uroliths, but that semiquantitative XRD analysis supplemented by accurate quantitative elemental data is more suitable for the precise determination of true stone composition.

Calcium Oxalate↗

PubMedDate not supplied

[Obtaining a reference pattern of rabbit brain thromboplastin].

Thromboplastin is a tissue extract used in the prothrombin time test (PT) necessary for oral anticoagulant control. The interlaboratory variability of the results of the PT test with thromboplastins of different tissue types, besides differences due to reporting PT in seconds or percentage, indicate the need for a standardized reference thromboplastin in order to express PT results on a common scale. The aim of the present work is to encourage the laboratory hospital either singly or in regional groups, to produce a standardized thromboplastin for their own use, to insure the control of oral anticoagulant therapy. Rabbit brain thromboplastin was prepared by Quick's technique. The reagent was calibrated against the international reference thromboplastin RBT/079, following the recommendations of the World Health Organization (WHO). Statistical analyses of the data were performed using an orthogonal regression. We obtained an international sensitivity index (ISI) of 2.177, a standard error of 0.0454 and a coefficient of variation of 2.09%. An international normalized ratio (INR) was also obtained for the conversion of measured PT to a common scale. The INNSZ thromboplastin is the first national reference preparation. With this reagent the introduction of an international scale for the control of oral anticoagulant therapy has become feasible in our country.

Animals↗

PubMed1994

MR diagnosis of meniscal tears of the knee: value of fast spin-echo vs conventional spin-echo pulse sequences.

OBJECTIVE: Contrast can be similar on fast spin-echo and conventional spin-echo MR images, but data acquisition is faster with fast spin-echo sequences. This study was designed to evaluate the performance of fast spin-echo sequences in the detection of meniscal tears in the knee, with the established conventional spin-echo technique used as a reference standard. SUBJECTS AND METHODS: We imaged 66 consecutive patients (129 menisci) who were referred for MR examination with suspected meniscal tears. We used our routine two-dimensional, multisection, long repetition time/double-echo spin-echo sequence and one of two fast spin-echo sequences. The fast spin-echo parameters were chosen to minimize the loss of high-resolution detail while otherwise maintaining the sequence as close as possible to the spin-echo sequence. We then did a retrospective evaluation of the fast spin-echo images, using the spin-echo images as the gold standard. RESULTS: Fast spin-echo images showed only 30 (65%) of the 46 meniscal tears seen on the conventional spin-echo images. In addition, four of the 30 tears seen with both sequences were diagnosed with greater confidence on the conventional spin-echo images. In the cases in which both sequences allowed a diagnosis of definite meniscal tear, the abnormalities tended to be more conspicuous on the spin-echo images. CONCLUSION: Our results suggest that the fast spin-echo sequence should not be used for the diagnosis of meniscal tears.

Adult↗

PubMed1985

Candidate reference method for determination of total bilirubin in serum: development and validation.

This candidate Reference Method for measuring total bilirubin in serum is based on the Jendrassik-Gróf principle (Clin Chem 29: 297-301, 1983). Standard Reference Material no. 916 bilirubin (National Bureau of Standards) is used as the standard. Bilirubin standard solutions may be prepared either in human serum or in 40 g/L albumin solution (human or bovine), because we found the molar absorptivity of the azopigment at 598 nm to be identical in these media. The absorptivities of the unconjugated and conjugated azopigments appear to be identical, but the conjugated azopigment is completely hydrolyzed in the final reaction mixture. Bilirubin added to serum from adults or neonates was quantitatively accounted for. Interference by hemoglobin (up to 2 g/L), ascorbic acid (up to 20 mg/L), or zinc (at physiological concentrations) is negligible. Of the therapeutic drugs we tested, only L-dopa and alpha-methyldopa interfere. We established normal adult reference values for total bilirubin and examined the intraindividual variation in 19 subjects.

Adult↗

PubMed2000

Sex differences in the growth of diabetic children.

To investigate the effect of diabetes on the growth of children and to detect possible impairment of their final height, 58 Chinese subjects (22 boys; 36 girls) with childhood diabetes were studied longitudinally from diagnosis. Mean onset age at presentation was 8. 70 years. All patients were measured and weighed at diagnosis and every 3-4 months during the follow up period. Their height and weight measurements were converted to standard deviation scores (S.D. S.) using normal height and weight-for-height reference standards for Chinese children established in Hong Kong. The mean height S.D.S. for boys and girls at diagnosis were +0.76 and -0.07 (P=0.015). The mean final height S.D.S. for boys and girls were +0.14 and -0.57. The final heights of girls were significantly shorter than their target heights. At attainment of final height for diabetic girls, their mean weight-for-height S.D.S. was +0.76 indicating that they tended to become overweight. This study demonstrates the sex differences in the growth of diabetic children. Diabetic boys were tall for age at presentation but they achieved average final heights while diabetic girls attained below average adult stature and they tended to become obese.

Adult↗

PubMed1991

Stable isotope dilution method for the determination of serum glucose using discharge-assisted thermospray liquid chromatography/mass spectrometry.

A discharge-assisted thermospray liquid chromatography/mass spectrometric method for the determination of serum glucose was studied. Isotope dilution technique was used with uniformly labelled (13C6) glucose as an internal standard. Successful liquid chromatography/mass spectrometry was achieved by post-column addition of aqueous ammonium acetate to the mobile phase. Quantification was performed by measuring the peak intensity ratios of the unlabelled and labelled [M + NH4]+ ions. Analytical results using the National Institute of Standards and Technology standard reference material serum showed satisfactory agreement with the certified value, and a relative standard deviation of about 1% was obtained.

Blood Glucose↗

PubMed2026

Which radiographic plane should be used to quantify the distal tibia angle on weightbearing CT images?

BACKGROUND: Precise quantification of distal tibial alignment is essential for planning corrective osteotomies and ankle joint replacement surgery. The lateral distal tibial angle (LDTA) is the principal radiographic parameter used for this purpose. While LDTA is increasingly measured on weightbearing cone-beam CT (WBCT) using two-dimensional coronal slices, the optimal measurement plane remains unclear. METHODS: In this retrospective comparative study, full-leg WBCT scans of patients scheduled for supramalleolar osteotomy (n = 20; mean age 47 ± 12.8 years) were analyzed. LDTA was measured on three coronal planes of the distal tibial plafond (anterior edge, mid-dome, posterior edge) and compared with semi-automated three-dimensional (3D) tibial alignment measurements as the reference standard. RESULTS: Mid-dome LDTA showed no significant difference from the 3D reference (p > 0.05) and demonstrated excellent agreement. Anterior measurements significantly overestimated LDTA, while posterior measurements underestimated it (both p < 0.05), with only fair agreement. CONCLUSION: LDTA should be measured at the mid-dome of the distal tibial plafond on WBCT to ensure accurate and reproducible alignment assessment. LEVEL OF EVIDENCE: Level III - Retrospective Comparative Study.

Humans↗

PubMed1996

Determination of lymphocyte immunophenotypic values for normal full-term cord blood.

Normal reference values for flow cytometric immunophenotypic lymphocyte markers for cord blood (CB) were determined using sufficient numbers of subjects for clinical laboratory use. Samples from 202 normal gestations were processed by whole blood lysis and analyzed in the following combinations: CD14/45, CD4/3, CD8/3, CD45RA/4, CD29/4, CD56/3, Cd19/3, CD19/10. Thirty-five adult laboratory volunteers were analyzed as controls. When compared to adults, CB showed increased relative percentages of naive T-helper cells, B cells, immature B cells, and CD8+3-cells and decreased T cells, cytotoxic T cells, activated T-helper cells, and large granular lymphocytes (CD56+3+). Significant differences were also found when CB samples were stratified by sex and race. These results provide clinical laboratory normal reference values for lymphocyte markers for CB, demonstrate the need for determining separate standard reference values for significantly different patient populations, provide the basis for future investigation of pathologic gestations and for clinical laboratory applications, and provide insight into early immunologic development.

Adolescent↗

PubMedDate not supplied

Antimicrobial susceptibility testing of anaerobic bacteria.

Antimicrobial susceptibility testing of anaerobic bacteria has assumed greater importance in recent years because of (1) an increase in recognition of the clinical significance of anaerobes, (2) a decrease in predictability of susceptibility patterns, (3) the appearance of new antimicrobial agents with variable activity against anaerobes, (4) an increase in use of and demand for susceptibility data by clinicians, and (5) the availability of a standardized reference and practical methods for susceptibility testing of anaerobes. The broth microdilution and broth disk-elution techniques are suitable for clinical microbiology laboratories and have been shown to provide results comparable to those obtained with the reference agar-dilution method developed by the National Committee for Clinical Laboratory Standards. The ability to produce beta-lactamase has been demonstrated in most strains of the Bacteroides fragilis group and in over half of other Bacteroides. Increasing resistance of B. fragilis to clindamycin has been reported, and the newer beta-lactam antibiotics, including moxalactam, piperacillin, cefoperazone, and cefotaxime, have variable activity against this organism. Most medical centers should perform susceptibility tests on anaerobes isolated from patients with bacteremia and bone and joint and central nervous system infections and on those anaerobes isolated in pure culture from other specimens and also should test anaerobic isolates on special request of clinicians.

Anti-Bacterial Agents↗

PubMed2006

Evaluation of reference-based two-color methods for measurement of gene expression ratios using spotted cDNA microarrays.

BACKGROUND: Spotted cDNA microarrays generally employ co-hybridization of fluorescently-labeled RNA targets to produce gene expression ratios for subsequent analysis. Direct comparison of two RNA samples in the same microarray provides the highest level of accuracy; however, due to the number of combinatorial pair-wise comparisons, the direct method is impractical for studies including large number of individual samples (e.g., tumor classification studies). For such studies, indirect comparisons using a common reference standard have been the preferred method. Here we evaluated the precision and accuracy of reconstructed ratios from three indirect methods relative to ratios obtained from direct hybridizations, herein considered as the gold-standard. RESULTS: We performed hybridizations using a fixed amount of Cy3-labeled reference oligonucleotide (RefOligo) against distinct Cy5-labeled targets from prostate, breast and kidney tumor samples. Reconstructed ratios between all tissue pairs were derived from ratios between each tissue sample and RefOligo. Reconstructed ratios were compared to (i) ratios obtained in parallel from direct pair-wise hybridizations of tissue samples, and to (ii) reconstructed ratios derived from hybridization of each tissue against a reference RNA pool (RefPool). To evaluate the effect of the external references, reconstructed ratios were also calculated directly from intensity values of single-channel (One-Color) measurements derived from tissue sample data collected in the RefOligo experiments. We show that the average coefficient of variation of ratios between intra- and inter-slide replicates derived from RefOligo, RefPool and One-Color were similar and 2 to 4-fold higher than ratios obtained in direct hybridizations. Correlation coefficients calculated for all three tissue comparisons were also similar. In addition, the performance of all indirect methods in terms of their robustness to identify genes deemed as differentially expressed based on direct hybridizations, as well as false-positive and false-negative rates, were found to be comparable. CONCLUSION: RefOligo produces ratios as precise and accurate as ratios reconstructed from a RNA pool, thus representing a reliable alternative in reference-based hybridization experiments. In addition, One-Color measurements alone can reconstruct expression ratios without loss in precision or accuracy. We conclude that both methods are adequate options in large-scale projects where the amount of a common reference RNA pool is usually restrictive.

Adenocarcinoma↗

PubMedDate not supplied

Experimental evaluation of different precision criteria applicable to microbiological counting methods.

The dispersion of microbiological counting measurements, when repeating the analysis on the same material both within a laboratory (repeatability) and between laboratories (reproducibility) can be characterized by the organization of interlaboratory studies, where several sets of identical test materials are sent to several laboratories. Using the example of data generated by an interlaboratory study on enumeration of Listeria monocytogenes in foods by the standardized reference method (colony-count technique), 2 types of robust estimators of reproducibility standard deviations, based on the median, were examined, in comparison with the classical estimators, based on the mean. Experimental evaluation indicated that the 3 approaches gave consistent results for most of the combinations. The usual log10 transformation of the enumeration results was also questioned before these calculations were conducted.

Algorithms↗

PubMed1984

Standards for growth in prepubertal primary school Kuwaiti children, a cross-sectional study.

In a cross-sectional study, anthropometric measurements were made in Kuwaiti primary school children aged six to nine years. The sample included 6765 children, of whom there were 3534 boys and 3231 girls. A minimum of 400 children were included in each of the 16 age-sex groups studied. Anthropometric data are presented as percentiles for weight-for-age, height-for-age, and weight-for-height. The results were smoothed and figures were constructed for the three growth standards. A comparison between locally constructed standards and a Western reference growth standard (Tanner et al.) revealed marked similarities in attainable growth. We think that the Western reference standards are suitable for use in Kuwait and probably in other similar developing countries, and the setting of lower targets for those countries is not recommended.

Age Factors↗

PubMed1992

Frozen human serum reference material for standardization of sodium and potassium measurements in serum or plasma by ion-selective electrode analyzers.

Three interlaboratory round-robin studies (RR1, RR2, and RR3) were conducted to identify a serum-based reference material that would aid in the standardization of direct ion-selective electrode (ISE) measurements of sodium and potassium. Ultrafiltered frozen serum reference materials requiring no reconstitution reduced between-laboratory variability (the largest source of imprecision) more than did other reference materials. ISE values for RR3 were normalized by the use of two points at the extremes of the clinical range for sodium (i.e., 120 and 160 mmol/L), with values assigned by the flame atomic emission spectrometry (FAES) Reference Method. This FAES normalization of ISE raw values remarkably improved all sources of variability and unified the results from seven different direct ISE analyzers to the FAES Reference Method value. Subsequently, a three-tiered, fresh-frozen human serum reference material was produced to the specifications developed in RR1-RR3, was assigned certified values for sodium and potassium by Definitive Methods at the National Institute of Standards and Technology (NIST), and was made available in 1990 to the clinical laboratory community as a Standard Reference Material (SRM); it is now identified as SRM 956. Albeit retrospectively, we show how applying an FAES normalization step identical to that used in RR4/5 to the ISE data for SRM 956 after the NIST Definitive Method values were known, consistently moved the ISE results for RR3 closer to the true value for Na+ and K+.

Electrodes↗

PubMed1993

Candidate reference methods for determining target values for cholesterol, creatinine, uric acid, and glucose in external quality assessment and internal accuracy control. II. Method transfer.

We describe the testing of transferability of candidate Reference Methods developed by INSTAND for cholesterol, creatinine, uric acid, and glucose. The methods are based on isotope dilution-gas chromatography--mass spectrometry. The study consisted of two parts: setup of the methods and self-evaluation for readiness in the collaborating laboratory, followed by independent measurements in parallel with INSTAND. Criteria used for judging the transferability and general reliability of the candidate Reference Methods were: the accuracy and precision of the collaborating laboratory and the agreement between the two laboratories. The accuracy was judged from the results on the Standard Reference Material 909 from the National Institute of Standards and Technology. For all analytes except glucose the bias from the certified value was < 0.7%. The mean intralaboratory imprecision ranged from 0.66% to 1.24%. The agreement between the results was tested by an advanced linear-regression analysis and Student's t-test. In general, the results demonstrate that the candidate Reference Methods developed by INSTAND can be successfully transferred without loss of their inherent precision and accuracy.

Blood Glucose↗

PubMed1996

Accuracy evaluation and hematocrit effect of commercial ionized calcium analyzers using Japanese serum reference material.

The serum reference material for concentration measurement of ionized calcium in blood has been established by our research group in Japan. The reference method used is the reference standard cell (RSC:IFCC/WGSE, Covington-Umemoto Cell) system. Here we present the results of the evaluation of accuracy using the serum reference material and the hematocrit effect of the nine commercial ionized calcium analyzers being used in routine measurements by Japanese round robin test program. The ionized calcium concentration and pH of two concentration levels of the reference material were analyzed in triplicate measurements according to the standard procedures designated by manufacturers. The effect of hematocrit in ionized calcium concentration measurement was tested using plasma and whole blood with hematocrit values of 35%, 50% and 65%, respectively. The range of bias of ionized calcium values were -0.14 approximately +0.09 mmol/L, -0.12 approximately +0.09 mmol/L for ionized calcium, respectively. The effect of hematocrit in ionized calcium concentration measurement was strongly observed in GEM Premier, CAI-101 and GASTAT-2 analyzers.

Calcium↗

PubMed1992

Left ventricular hypertrophy in black and white hypertensives. Standard electrocardiographic criteria overestimate racial differences in prevalence.

OBJECTIVE: To assess racial differences in the accuracy of standard electrocardiographic (ECG) criteria in the diagnosis of left ventricular hypertrophy (LVH). DESIGN: The sensitivity and specificity of standard ECG criteria were compared in blacks and whites using echocardiographic LVH as the reference standard. SETTING: Eight worksite-based hypertension clinics in New York, NY. PATIENTS: A sample of 122 black and 148 white hypertensive patients. RESULTS: The prevalence of ECG-LVH was two to six times higher in blacks than in whites, depending on the criteria used (range, 6% to 24% in blacks vs 1% to 7% in whites; P = .0005 to .19 for black-white comparisons). The difference in prevalence of echocardiographic LVH [corrected], however, was less striking and did not attain statistical significance (26% in blacks and 20% in whites; P greater than .2). The sensitivity of the ECG was low (range, 3% to 17%) and did not differ significantly between the two races for any of the conventional criteria; specificity, however, was lower in blacks for all criteria (range, 73% to 94% vs 95% to 100% for whites; P = .0001 to .09). The predictive value of a positive ECG was consistently, although not significantly, lower in the black subjects. Black race was the strongest independent predictor of decreased ECG specificity in multiple logistic regression analysis that also considered age, gender, body mass index, left ventricular mass index, and smoking. CONCLUSIONS: Commonly used ECG criteria for the detection of LVH have a poor sensitivity in both black and white hypertensives and a lower specificity in blacks than in whites; this may lead to a greater number of false-positive diagnoses in black patients, as well as to an overestimation of black-white difference in LVH prevalence.

Black People↗

PubMed2000

Isotopic analysis of uranium in U3O8 by passive gamma-ray spectrometry

Passive gamma-ray spectrometry was applied to analyze the isotopic composition of uranium in U3O8. Depleted and enriched U3O8 standard reference materials were used to calibrate the system. An independent calibration was performed by standard gamma-ray point sources. U3O8 SRM samples of the 950 series were analyzed. The present results show that the isotopic abundances of 235U in SRMs 950, 950a and 950b are higher by +3.6, +0.9 and +0.9% (relative deviation) than the natural value 0.7200%, while relative precisions were +/-0.4, +/-0.7 and +/-0.3%, respectively.

Journal Article↗

PubMed2002

Diversion of first blood volume results in a reduction of bacterial contamination for whole-blood collections.

BACKGROUND AND OBJECTIVES: In a previous study we established a reliable setpoint for the prevalence of bacteria in whole blood. In the present study we investigated the possible preventive effect, of diversion of the first 10 ml of a blood donation, on the bacterial contamination rate. MATERIALS AND METHODS: To divert the first 10 ml of a whole-blood donation, we used a special five-bag system equipped with a Composampler device. After venepuncture, the first 10 ml of a donation was sampled into a vacutainer tube. This was followed by the collection of the whole-blood unit. The extra bag allowed direct sampling of the final donation in a closed system for BacT/Alert. Whole-blood samples were taken after storage (2-14 h at 20 degrees C) and subsequent mixing. BacT/Alert culture bottles were incubated until positive, or for 7 days if negative. Confirmation and identification of positive cultures was performed according to internationally recognized standard reference methods. RESULTS: The prevalence of bacteria in whole blood, as determined by using standard collection techniques, was 0.35% (95% confidence interval 0.27-0.44%, n = 18 257). After diversion of the first 10 ml this value was significantly lower: 0.21% (P < 0.05, 95% confidence interval 0.12-0.35%, n = 7087). Most strikingly, a reduction in the frequency of staphylococcal species was observed (P < 0.02, reduction from 0.14 to 0.03%). CONCLUSIONS: Diversion of the first 10 ml of blood was shown to contribute significantly to a reduction in the prevalence of superficial skin bacteria in whole-blood units. In our opinion, blood collection systems should be adapted to use the first 10-30 ml of a whole-blood donation for testing purposes.

Bacterial Infections↗