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At least 91 records · Page 5Linked to original sources
PubMed1980

Sources of error in the isotopic cholesterol balance method in African green monkeys consuming a cholesterol-free diet.

Six African green monkeys were labeled intravenously with [1,2-(3)H]cholesterol while consuming a cholesterol-free liquid formula diet. The plasma cholesterol specific activity was compared with the specific activity of the biliary cholesterol and bile acids and with the fecal neutral steroids in order to determine whether the traditional isotopic balance method was valid for the calculation of endogenous cholesterol excretion. The specific activity of biliary cholesterol and bile acids averaged 10-15% lower than plasma cholesterol specific activity. Fecal cholesterol and coprostanone specific activities were similar to that of the biliary cholesterol, but the specific activity of fecal coprostanol was approximately 25% lower. This suggests that biliary cholesterol and bile acids were derived from a pool of hepatic cholesterol that did not completely equilibrate with the whole body exchangeable cholesterol pool. In addition, there was further reduction in the specific activity of coprostanol, the major fecal neutral steroid, presumably by cholesterol synthesized in the lower intestine and preferentially converted to coprostanol. As a result, the traditional isotopic balance procedure underestimated endogenous neutral steroid excretion by 46% and bile acid excretion by 31% in African green monkeys fed the cholesterol-free diet. Within 7 days after the addition of 1 mg cholesterol/kcal to the diet, the specific activities of plasma and biliary cholesterol and biliary bile acids were identical and there was no difference in the specific activities of the individual fecal neutral steroids. Thus, the traditional isotopic balance procedure (DPM fecal neutral steroids + bile acids/specific activity [DPM/mg] plasma cholesterol) can be used for calculation of endogenous cholesterol excretion in cholesterol-fed animals during the nonsteady state when plasma cholesterol concentrations are rapidly increasing, as well as after a new steady state has been achieved.-Henderson, G. R., and R. W. St. Clair. Sources of error in the isotopic cholesterol balance method in African green monkeys consuming a cholesterol-free diet.

Animals↗
PubMed1994

Saline PCO2 is an important source of error in the assessment of gastric intramucosal pH.

OBJECTIVE: To determine whether the measurement error of saline PCO2, using blood gas analyzers, is relevant for the interpretation and clinical use of the gastric intramucosal pH measurement. DESIGN: A comparison of four different blood gas analyzers (ABL-520, Ciba Corning, IL-1302, and Nova), using tonometered saline as the reference. SETTING: Clinical laboratory of a university hospital intensive care unit. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The bias and the precision of each blood gas analyzer was determined for measurements of PCO2 in saline samples. These samples had been balanced to PCO2 levels of 30, 45, and 68 torr (4, 6, and 9 kPa, respectively). In addition, the effect of buffering the saline was evaluated. The bias of the PCO2 measurement increased (p < .001) at the higher PCO2 levels. The bias ranged from -5.2 to -25.9 torr (-0.69 to -3.45 kPa) at a PCO2 of 45 torr (6 kPa) and from -5.2 to -33.1 torr (-0.69 to -4.41 kPa) at a PCO2 of 68 torr (9 kPa), and there was a significant (p < .001) analyzer-PCO2 level interaction. The type of the analyzer also influenced the bias (p < .001). The Nova analyzer underestimated the PCO2 by 50% to 60%. The other analyzers underestimated the PCO2 by 5% to 19%. The use of the buffer reduced the bias of all analyzers (p < .001). Based on the precision of the saline PCO2 measurement, a difference in gastric intramucosal pH of 0.06 pH units can be reliably detected at a PCO2 of 45 torr (6 kPa) by all analyzers, with the exception of the Nova analyzer. CONCLUSIONS: Measurement of saline PCO2 is an important source of error in the assessment of gastric intramucosal pH, and the error depends on both the analyzer used and the actual PCO2 level. Direct comparison of pH values obtained by different analyzers is not valid. Changes in gastric intramucosal pH of 0.06 pH units can be detected by most analyzers in the clinically relevant PCO2 level.

Analysis of Variance↗
PubMed1976

Bubbles in samples for blood gas determinations. A potential source of error.

The presence of small gas bubbles in devices used to collect blood gas samples is considered. A gas bubble whose relative volume is 0.5 to 1% or more that of the liquid in the collection device is a potential source of significant error. Relationships describing the possible magnitude of this error are derived and substantiated.

Blood↗
PubMed1987

Sources of error and variability in the determination of anaerobic threshold in healthy humans.

The derivation of anaerobic threshold (AT) from the ventilatory responses to incremental exercise is associated with several sources of variability including true biological variability and the error attributable to the observer interpretation of data. To define and quantitate the sources of variability in AT determination we exercised 6 healthy volunteers 6 times and submitted plots of ventilation (Ve), CO2 production (VCO2), respiratory exchange ratio (R) and the ventilatory equivalent for oxygen (Ve/VO2) in random order to 4 independent observers. Within-subject variability in AT ranged from 7 to 55% depending on the subject, ventilatory parameter and observer with an overall mean coefficient of variability of 24%. Significant day-to-day variability was demonstrated in 4 of the 6 subjects using AT values derived from at least one of the ventilatory parameters (Anova, p less than 0.05-p less than 0.001). Mean values for AT obtained with the Ve and VCO2 plots (1.91 and 1.69 liter/min VO2) were significantly lower than those obtained from R and Ve/VO2 plots (2.28 and 2.6 liters/min VO2; p less than 0.001, Anova). Anova showed significant differences in AT values derived by one of the observers compared to the other three (p less than 0.001). A significant observer/ventilation parameter interaction was also found (p less than 0.001) due to one observer consistently estimating higher values of AT from the R plots. The observer error in deriving AT from each exercise test using the Ve plots = 24%, for VCO2 = 19% for R = 29% and for Ve/VO2 = 15%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1977

Stainable iron in aspirated and needle-biopsy specimens of marrow: a source of error.

Marrow iron was assessed in needle biopsy sections and in simultaneously obtained aspirated smears and aspirated clot sections from 251 patients. Significantly different amounts of stainable iron were observed in needle biopsy sections and aspirated smears in 15% of the specimens. The usual difference consisted of significantly less stainable iron in needle biopsy sections as compared to the aspirated smears (13%). Of clinical importance was the finding of absent stainable iron in 8% of the needle biopsy sections, in contrast to the definite deposits observed in the corresponding aspirated smear. Of similar interest was the observation that 6% of the needle biopsy sections had significantly less stainable iron than corresponding hemosiderotic smears. The amounts of stainable iron in needle biopsy sections were similar to the amounts observed in the corresponding aspirated clot sections. Evaluation of marrow iron using needle biopsy sections as well as aspirated clot sections differs from results observed in aspirated smears and could be a source of significant error in the assessment of iron stores.

Biopsy, Needle↗
PubMed1988

Source of error in clinical assessment of innominate rotation. A special communication.

The sacroiliac joint (SIJ) is a possible source of low back pain or dysfunction. Various methods of visually assessing the relative position of the innominate to the sacrum have been used to evaluate SIJ dysfunction. The purpose of this special communication is to describe how a false-positive interpretation of innominate rotation may occur when a leg-length difference exists and visual assessment is used.

Adult↗
PubMed1992

Estimating total analytical error and its sources. Techniques to improve method evaluation.

The process of method evaluation starts with identifying goals either to demonstrate the clinical validity of an assay or to identify assay error sources that require improvement. Taguchi's idea of continual quality improvement vs the notion of meeting or failing specification has been applied to clinical chemistry. In this article, I propose a model of assay performance that includes the terms random interferences and protocol-specific biases (a series of systematic errors). I explain these terms, as well as the consequences of failing to consider them. To validate an assay clinically, I recommend direct estimation of total analytical error from a method comparison. To identify assay error sources that require improvement, I recommend a multifactor protocol (in addition to a method comparison). Individual error sources are related to total analytical error with the use of an error propagation technique. Much of the proposed data analysis techniques are straightforward but not routinely practiced. I demonstrate principles with the use of a cholesterol assay.

Chemistry, Clinical↗
PubMed1985

Basilar venous plexus of the posterior fossa: a potential source of error in petrosal sinus sampling.

Sampling of serum from the inferior petrosal sinus can provide important information about the source of elevated adrenocorticotropic hormone (ACTH) levels. This often leads to improved results of pituitary surgery for Cushing disease. The authors describe a successful catheterization technique and illustrate the venous anatomy of the inferior petrosal sinuses and basilar plexus.

Adenoma↗
PubMed1984

Improved techniques for the photometric determination of partition coefficients, with particular reference to the chloroform-ammonia solvent system.

Accurate partition coefficients K = Corg/Caq in chloroform-ammonia can be obtained by measuring the absorbance of the aqueous layer, replenishing with fresh aqueous solvent, and remeasuring the absorption after reequilibration. Provided the solute has a reasonably strong UV absorption, only 0.1-5 mg of material is required. Neither the amount, the extinction coefficient, nor (in most cases) the purity of the substrate material need be known. In general, K values ranging from 100 to 0.01 can be measured with a precision of greater than or equal to 10%. A detailed analysis of the absorbance and volumetric error sources permits the optimum combination of experimental conditions such as volume ratios, cell lengths, and absorbance (either direct or differential, or with scale expansion) to be predicted a priori. Quantitative estimates for all primary error sources, such as photometric precision, baseline error, stray light, and volumetric errors were also experimentally determined. The theoretical error model was tested by determining K for aniline under widely ranging experimental conditions and by comparing the experimental standard deviations with those calculated from the theoretical model. The agreement was found to be satisfactory. The method described appears to be of particular usefulness for the determination of extraction or chromatographic parameters of basic drugs.

Ammonia↗
PubMed1991

Sources of error in the quantitative analysis of MRI scans.

The increasing use of quantitative analysis of MRI scans in the literature has produced a need to identify potential sources of bias in such analysis procedures. Six sources of bias are demonstrated in this paper. These include bias attributable to partial volume effects, head tilt, plane of view, use of noncontiguous slices, contrast/intensity manipulations, and magnetic inhomogeneities. The magnitude of bias for each source varied according to whether a hemisphere or regions within a hemisphere were measured, with regional effects typically exceeding hemisphere effects.

Bias↗
PubMed1986

[The indirect solid-phase method of immunoenzyme analysis, its accuracy and sources of error].

The study of the accuracy of the enzyme-linked immunosorbent assay has revealed that the accuracy of this assay is low. The influence of instruments (dispensers, photometers, plates) on the accuracy of the assay has been studied. As shown in this study, the main sources are titration procedures and differences in the adsorption and optical properties of available plates, those manufactured in the USSR giving greater errors.

Adsorption↗
PubMed1977

Temperature dependence of the absorbance of alkaline solutions of 4-nitrophenyl phosphate--a potential source of error in the measurement of alkaline phosphatase activity.

The absorbance of an alkaline solution of 4-nitrophenyl phosphate is a function of temperature. Quantitative evaluation of this phenomenon indicates that it (a) depends on the concentration of the compound and is independent of source, buffer concentration, and pH above 9.0; (b) is reversible; (c) is not a result of alkaline hydrolysis or 4-nitrophenol contamination; and (d) correlates with a temperature-induced shift of its absorbance spectrum. The phenomenon may represent a potential analytical problem in methods for alkaline phosphatase in which this compound is the substrate. If thermal equilibrium is not reached and maintained during an alkaline phosphatase assay, the thermochromic response will be included in the measured rate. The magnitude of this error depends on the thermal response and control characteristics of each particular instrument and the reaction conditions under which such an analysis is performed.

Alkaline Phosphatase↗
PubMed1989

Age: a truly confounding variable.

As Hinshaw (1981) has noted, the process of designing research might best be conceptualized as a series of informed decisions that involve constant trade-offs and compromise. With each advantage gained by a particular theoretical or methodological decision, the researcher inherits a certain number of threats to the study's internal and external validity and a potential number of error sources. Because of the nature of the research questions of interest to nurses and because of situational and contextual constraints in the clinical setting, nurse researchers often are required to select samples that contain small or large proportions of elderly subjects. The purpose of this article has been to raise some of the theoretical and methodological issues associated with the selection of both age-heterogeneous samples and age-homogeneous samples. Although in research all possible error sources cannot be controlled, it is possible to reduce the amount of error by a clear understanding of the implications of choices regarding age-related issues and inclusion of design features that reduce the amount of error introduced when research subjects who are relatively young are studied along with research subjects who are elderly.

Adult↗
PubMed1994

Source monitoring during name recognition in older adults: psychometric and electrophysiological correlates.

The hypothesis that source monitoring in older adults is specifically related to frontal lobe function was tested. In a fame-judgment task, older adults' ability to monitor the source of name familiarity was independent of their short-term recognition ability. Source errors were not related to performance on the Wisconsin Card Sorting Test, a psychometric index of frontal function, or to the initial orienting response of the contingent negative variation (CNV), a frontally based electrophysiological measure, even though these "frontal" measures were reliably related to each other. Source error was predicted by the latter portion of the CNV, the expectancy response, and by the Benton Facial Recognition Test, a visuoperceptual task not typically linked to frontal function. These data suggest that the accuracy of source attribution in older adults depends on various attentional control processes, not all of which may be frontally based.

Aged↗
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↗