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At least 163 records · Page 9Linked to original sources
PubMed1976

Sources of error in glucose determinations in neonatal blood by glucose oxidase methods, including Dextrostix.

An investigation was carried out to examine why a glucose oxidase-peroxidase-orthodianisidine method for plasma glucose, without protein precipitation, gave low results for neonatal blood. The magnitude of the difference between the results with and without protein precipitation was examined in a clinical neonatal series, and in sera to which bilirubin, hemolysate, pure hemoglobin, and uric acid had been added. Systematic linear inhibition was demonstrated with bilirubin, and the results suggested that high concentrations of hemolysate and uric acid could also interfere. Use of alkaline protein precipitants eliminated the inhibition. Dextrostix test results for neonatal blood are compared with results of conventional glucose analyses and possible sources of discrepancy examined.

Bilirubin↗
PubMedDate not supplied

A serious source of error in antiglobulin testing.

The investigation of a failure of proficiency showed that certain saline solutions are inappropriate for use in blood group serology tests. In particular, it was found that solutions of unexpectedly low pH and/or those autoclaved and stored in plastic containers could severely compromise the sensitivity of the antiglobulin test when used as wash solutions. The observed loss of sensitivity ranged from a reduction in titration score to a complete failure in the detection of clinically significant blood group antibodies. It is suggested that careful consideration should be given to the source, pH, and storage container of saline solutions intended for use in serological tests and that improved standardization and sensitivity could be achieved by using phosphate-buffered saline pH 7.0 to 7.2 for all such purposes. It is recommended that unbuffered saline solutions of pH less than 6.0 should not be used for serological testing.

Blood Group Antigens↗
PubMed2002

The role of collaborative planning in children's source-monitoring errors and learning.

The aim of this research was to provide empirical evidence for a cognitive process that may contribute to children's learning from another person. A cornerstone of Vygotsky's sociocultural theory is that knowledge is internalized from others; however, the cognitive processes that support this transformation are underspecified. In a series of three studies, kindergarten children (mean age 5 years 8 months) participated in a categorization task with an adult in several collaborative and noncollaborative conditions and then were tested on their memory of who had performed which actions in the task. After the memory task, children were asked to recategorize the items on their own. Source-monitoring patterns and children's learning varied across conditions according to predictions. A measure of recoding was related to children's planning language that, in turn, predicted learning among the children. The results suggest that one process that contributes to children's internalization of knowledge may involve recoding of agent information and that recoding can be indexed by source-monitoring performance.

Child↗
PubMed2000

Source of error in calculation of optical diffuse reflectance from turbid media using diffusion theory.

Diffusion theory and similarity relations were used to calculate the optical diffuse reflectance of an infinitely narrow laser beam incident upon a semi-infinite turbid medium. The results were analyzed by comparison with the accurate results from Monte Carlo simulations. Because a large number of photon packets were traced, the variance of the results from Monte Carlo simulations was small enough to reveal the detailed defects of the diffusion theory and the similarity relations, which are broadly used in photomedicine. We demonstrated that both diffusion theory and similarity relations provide very accurate results when the photon sources are isotropic and buried more deeply than one transport mean free path in turbid media. We found that the key factor affecting the accuracy of the diffusion theory application was the conversion from the infinitely narrow laser beam to an isotropic point source in turbid media.

Computer Simulation↗
PubMed2000

Statistical motor unit number estimation: reproducibility and sources of error in patients with amyotrophic lateral sclerosis.

The reliability of motor unit number estimation (MUNE) for assessment of the long-term course of ALS is dependent on the reproducibility of the technique. We report our results with the statistical method of MUNE on the ulnar nerve/hypothenar muscle in 16 ALS patients who were studied on 52 occasions. On each occasion, MUNE was performed twice with one electrode placement and once with a different placement. For each MUNE, mean surface motor unit potential amplitude was determined within three different recording ranges or windows at different stimulus intensities. The MUNE results had excellent reproducibility with coefficients of variation of 19% and test-retest correlation coefficients from 0.75 to 0.86. With examination of sources for variability, the reproducibility of statistical MUNE is not affected by minor variation in stimulation and recording electrode placement but may be improved by modifying methods for recording window selection. The high reproducibility of statistical MUNE supports its reliability for estimating the rate of motor unit loss in ALS.

Algorithms↗
PubMed2001

A convenient method for detecting electrolyte bridges in multichannel electroencephalogram and event-related potential recordings.

Dense electrode arrays offer numerous advantages over single channel electroencephalogram/event-related potential (EEG/ERP) recordings, but also exaggerate the influence of common error sources arising from the preparation of scalp placements. Even with conventional low density recordings (e.g. 30-channel Electro-Cap), over-application of electrode gel may result in electrolyte leakage and create low impedance bridges, particularly at vertically-aligned sites (e.g. inferior-lateral). The ensuing electrical short produces an artificial similarity of ERPs at neighboring sites that distorts the ERP topography. This artifact is not immediately apparent in group averages, and may even go undetected after visual inspection of the individual ERP waveforms. Besides adding noise variance to the topography, this error source also has the capacity to introduce systematic, localized artifacts (e.g. add or remove evidence of lateralized activity). Electrolyte bridges causing these artifacts can be easily detected by a simple variant of the Hjorth algorithm (intrinsic Hjorth), in which spatial interelectrode distances are replaced by an electrical analog of distance (i.e. the variances of the difference waveforms for all pairwise combinations of electrodes). When a low impedance bridge exists, the Hjorth algorithm identifies all affected sites as flat lines that are readily distinguishable from Hjorth waveforms at unbridged electrodes.

Algorithms↗
PubMed1997

Caffeine in saliva after peroral intake: early sample collection as a possible source of error.

The influence of collection time on the correlation of caffeine concentrations in saliva and serum was examined in six healthy adults after peroral administration of 5 mg/kg caffeine citrate. Saliva was obtained from three different salivary glands (sublingual, right parotid, and left parotid) and evaluated separately. Caffeine concentrations in saliva and serum samples were determined by high-performance liquid chromatography. There were no differences in the caffeine concentrations in saliva from the three investigated glands (alpha = 0.05). Saliva samples collected earlier than 2 hours after caffeine intake showed higher caffeine concentrations than could be expected from the corresponding serum samples. Gingiva contamination was shown to be responsible for the higher caffeine concentrations in saliva, and it was concluded that saliva is a feasible matrix for therapeutic drug monitoring of caffeine. If caffeine is administered orally, saliva samples should be taken at least 2 hours after caffeine intake. If caffeine-containing beverages are used as the source of caffeine or if subjects do not cooperate by rinsing the mouth of caffeine contamination, an additional 60 minutes should be added before saliva sampling.

Administration, Oral↗
PubMed2000

Dipole location errors in electroencephalogram source analysis due to volume conductor model errors.

An examination is made of dipole location errors in electroencephalogram (EEG) source analysis, due to not incorporating the ventricular system (VS), omitting a hole in the skull and underestimating skull conductivity. The simulations are performed for a large number of test dipoles in 3D using the finite difference method. The maximum dipole location error encountered, utilising 27 and 53 electrodes is 7.6 mm and 6.1 mm, respectively when omitting the VS, 5.6 mm and 5.2 mm, respectively when neglecting the hole in the skull, and 33.4 mm and 28.0 mm, respectively when underestimating skull conductivity. The largest location errors due to neglecting the VS can be found in the vicinity of the VS. The largest location errors due to omitting a hole can be found in the vicinity of the hole. At these positions the fitted dipoles are found close to the hole. When skull conductivity is underestimated, the dipole is fitted close to the skull-brain border in a radial direction for all test dipoles. It was found that the location errors due to underestimating skull conductivity are typically higher than those found due to neglecting the VS or neglecting a hole in the skull.

Electric Conductivity↗
PubMed1999

High affinity binding of fluorescein isothiocyanate to eosinophils detected by laser scanning cytometry: a potential source of error in analysis of blood samples utilizing fluorescein-conjugated reagents in flow cytometry.

BACKGROUND: In samples of peripheral blood cells processed using the commercial kits for detection of apoptosis based on DNA strand break labeling, a subpopulation of cells characterized by high green fluorescence, similar in intensity to that of apoptotic cells but more uniform, was consistently observed by flow cytometry. The labeled cells had no other features of apoptosis. The labeling was observed regardless of the fixative used and was evident in control samples lacking terminal deoxynucleotidyltransferase. Common to all the kits that generated this labeling pattern was the presence of fluorescein (f) conjugated reagents, f-dUTP, f-avidin, or f-antibody. METHODS: Laser scanning cytometry was used to identify the labeled cells and study the mechanism of labeling. Because it was suspected that the traces of unconjugated f-isothiocyanate (FITC) that may contaminate the reagents were responsible for the labeling, FITC binding affinity to white blood cells was studied. Gel electrophoresis was used to detect the presence of unconjugated FITC in the reagents. RESULTS: After staining with Giemsa, the strongly fluorescent objects were identified as eosinophils with normal morphology and no evidence of apoptosis. The fluorescence was localized exclusively within the cytoplasmic granules. Labeling of eosinophils was observed at 2 nM concentration of FITC, which was over three orders of magnitude lower than that needed to label neutrophils, monocytes, or lymphocytes. Gel electrophoresis of the f-conjugated reagents revealed only minor contamination with FITC. CONCLUSIONS: (1) Trace amounts of unconjugated FITC contaminating the reagents are adequate to strongly label eosinophils thereby introducing experimental bias in analysis of apoptosis and in other studies on blood cells utilizing f-labeled antibodies, e.g., in detecting cytokines. (2) FITC at concentration 2-500 nM can be used as a marker of eosinophiles; (3) Because of high affinity to FITC, eosinophiles (or the protein from these cells) may serve as a means of removing traces of unconjugated FITC from the reagents during their manufacture or prior to use.

Apoptosis↗
PubMed2000

Incidental sampling of branchial remnants: a potential source of error in fine-needle aspiration of neck lesions-a case report.

Remnants of the branchial apparatus can produce lesions in the head and neck region in later life, often amenable to fine-needle aspiration (FNA) diagnosis. Yet such remnants or rudimentary lesions can remain clinically undetected and can later interfere with the cytologic interpretation of other deep lesions of the neck, as the present case demonstrates. In this case the lesion, which by a subsequent resection turned out to be a neurilemmoma, had been adequately sampled by the FNA, yet the cytologic diagnosis was sidetracked by the presence in the specimen of immature squamous epithelial tissue fragments and other elements (multinucleated histiocytes, calcifications), on the basis of which the diagnosis of an epithelial lesion, likely malignant, was made. The neck surgery and a preceding endoscopic examination of the mouth, pharynx, and larynx did not identify such a lesion, but a detailed microscopic examination of the fibroadipose tissue between the tumor and the peripharyngeal region revealed the presence of epithelial microfragments with morphology partly corresponding to that of the FNA cytology, highly indicative of a branchiogenic lesion in the peripharyngeal region. The basic embryology of the branchial apparatus resulting in such defects is presented, as well as tentative guidelines for recognizing material deriving from accidental sampling of such lesions during FNA investigations of deep-seated masses of the neck. Diagn. Cytopathol. 2000;22:157-160.

Aged↗
PubMed1980

Possible sources of error in the evaluation of psychopathology.

Mental health professionals have been described as biased in the evaluation of mental illness, almost always in favor of illness. It is a professional bias does exist, two factors could be responsible--situational expectancies and/or professional training. Undergraduate students (N = 32) and psychiatric residents (N = 16) listened to four recorded interviews. Two levels of mental illness expectany were obtained by changing the context of the interviews. The Ss rated the interviewees on scales of psychopathology and recorded their impression of the interviewees. Multivariate and univariate analysis of variance and chi 2 tests were used to evaluate the data. Evidence indicated that the biased perception of mental illness occurred for all Ss when mental illness expectancies were high. The data also indicated that residents are not more inclined than students to label people mentally ill.

Attitude of Health Personnel↗
PubMed1989

Measurement of coronary sinus flow by thermodilution: observations on the effect of respiration and a review of the potential sources of error.

In a series of experiments involving measurement of left ventricular blood flow by thermodilution in the coronary sinus, a consistent, but unexpected, variation in calculated coronary sinus flow, related to respiration, was seen. In some patients the variation was small, but in others it was as much as 300%. To discover its cause, five patients were investigated prospectively with continuous right atrial pressure monitoring during coronary flow measurement and respiratory manoeuvres. In three, ice-cold saline was injected into the right atrium during respiratory manoeuvres while coronary sinus temperature was monitored continuously and the position of the catheter was monitored fluoroscopically. The cause was found to be movement of the catheter such that thermistor approached the right atrium, and the variation was therefore spurious. We report these findings and discuss other known causes of inaccurate coronary flow measurement using the thermodilution technique.

Blood Flow Velocity↗
PubMed1993

Sources of error in quantitative coronary angiography.

Many studies have reported the accuracy of quantitative coronary angiography (QCA) based on experiments using moderated-size phantoms imaged under unrealistic radiographic conditions. However, these observations may not be generalizable to the setting of clinical angiography. To determine QCA accuracy in a realistic radiographic setting and evaluate the impact of the x-ray system line spread function, plexiglass phantoms were imaged inside and out of a human thorax. A realistic radiographic background was associated with a 38% increase in variability of results (p < 0.05). Low concentrations of contrast and large image intensifier input screens were associated with significantly larger errors and variability in results (p < 0.05). There was a systematic overestimation of diameter in the smallest phantom. A mathematical model of the x-ray line spread function was developed that explains the observed overestimation of the smallest phantom and provide a rational approach for correction of the line spread function for QCA. Many factors encountered in clinical coronary angiography such as nonuniform radiographic background, low concentrations of contrast, and small vessel diameters have a significant adverse impact on the accuracy and/or variability of gradient-based edge detection QCA systems.

Artifacts↗
PubMed1983

Accuracy of various techniques in the measurement of the duration of the Q wave: a possible source of error in diagnosing myocardial infarction by electrocardiography.

The method of measuring the width of the Q wave on electrocardiogram is one of the variables contributing to conflicting findings regarding the accuracy of the ECG in the diagnosis of myocardial infarction. This study assesses the accuracy of a variety of methods of measuring the width of the Q wave recorded by direct-writing electrocardiographic instruments. The assessment was made by comparing the width of the Q wave as inscribed by thermal direct-writing electrocardiographs to the width of the Q wave as measured from an oscilloscopic display, the latter representing the "true" width of the Q wave. The measurement of the width as obtained from the upper edge of the tracing obtained with direct-writing electrocardiographs underestimated the true width of the Q wave, while the opposite was the case by measuring the width along the lower edge of the tracing. The most reliable ways to obtain the true width of the Q wave are: (1) to average the measurements as obtained along the upper and lower edge, (2) to measure the width along an ideal line in the middle of the tracing, or (3) to measure the width along the trailing edge of the deflection.

Diagnostic Errors↗