PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Error Sources”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 55 records · Page 3Linked to original sources
PubMed1986

Heterophilic antibody as a source of error in immunoassay.

We describe our experience with a young woman believed to be hypothyroid and menopausal because of erroneously elevated TSH, LH, and FSH estimates. These errors were found to be due to the presence of antibodies to rabbit IgG in the patient's blood. We found that antibody-limited assays for TSH, LH, and FSH using antisera raised in rabbits were affected by this problem unless rabbit IgG was included, whereas antibody-excess assays were not. These problems were most simply detected by observing inappropriate results when measurements were made in dilutions of the patient's serum. The presence of endogenous antibody directed against antibodies used in immunoassays is a significant potential source of error requiring awareness on the part of both the clinician caring for such patients and the clinical laboratory making the measurements.

Adult↗
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↗
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↗
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↗
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↗
PubMed1987

Arm position as a source of error in blood pressure measurement.

The present study was designed to assess the value of correct positioning of a patient's arm when measuring blood pressure (BP). A total of 181 subjects were examined, 141 hypertensives on treatment, 25 untreated hypertensives, 15 normotensives. All the subjects underwent three BP measurements after a 5-min resting period in supine position. Then two BP readings were recorded in standing position with the arm either positioned by the patient's side or supported passively at patient's heart level. Average systolic BP (SBP) in standing position were 144.6 +/- 20.2 mmHg with the arm at the side and 136.4 +/- 21.1 mmHg with the arm at the heart level (p less than 0.001); average diastolic pressures were 99.0 +/- 12.0 mmHg and 90.2 +/- 12.3 mmHg (p less than 0.001), respectively. A fall in SBP greater than or equal to 20 mmHg from the supine to the upright position was detected in 18.2% of cases when measurement was performed at heart level; such a reduction was inapparent in two-thirds of cases when the arm was placed at the patient's body side. Incorrect positioning of a patient's arm during BP measurements in standing position leads to overestimation of BP values and masks the presence of postural hypotension.

Adult↗
PubMedDate not supplied

Color and conventional image-directed Doppler ultrasonography: accuracy and sources of error in quantitative blood flow measurements.

Accuracy of two systems--conventional (DRF 400, Diasonics) and color-coded (Angiodynograph, Quantum/Phillips) image-directed Doppler ultrasonography--was investigated using an in vitro model that generated both monophasic and triphasic pulsatile flow patterns. Estimated and actual blood volume flow rates showed good correlations, but the sampling with a hand-held transducer led to wide variations in measurement error for the conventional (-69.2% to 50%) and the color-coded (-79.3% to 265.7%) systems. By performing multiple measurements, one could improve accuracy considering only the maximal values of a series instead of the mean values. Accuracy was impaired by interposed muscular or fatty tissue due to false low time-average velocity measurements caused by a loss of Doppler signal. Comparison of both systems revealed significant differences between pulsatility index values (p less than 0.001), blood flow velocities (p less than 0.001), and blood volume flow rates (p less than 0.05 for program flow, p less than 0.001 for manual and automatic flow program of the color-coded system).

Blood Flow Velocity↗
PubMed1986

Endogenous thymidine and hypoxanthine are a source of error in evaluating methotrexate cytotoxicity by clonogenic assays using undialyzed fetal bovine serum.

None of 13 fresh human tumor samples of various histology cloned in a two-layer agar culture system with 20% undialyzed fetal bovine serum (FBS) showed sensitivity to three antifolates, methotrexate (MTX), trimetrexate and 5,8-dideazaisofolic acid (IAHQ), even after continuous exposure to the highest concentrations (100 microM) for 21 days. In order to investigate this lack of antifolate drug effect, we compared the toxicity of continuous MTX exposure in the human colon carcinoma cell line HCT-8, cloned in a thymidineless medium (RPMI 1640) supplemented with 10% horse serum (HS), 10% fetal bovine serum (FBS), 20% FBS or 20% dialyzed FBS. In the presence of native FBS, when the minimum clone size was set at 30 cells/colony, the survival of HCT-8 cells reached a plateau at approximately 60% of untreated control after exposure to MTX concentrations between 0.1 microM and 100 microM. Only when the minimum clone size was set at 2 X 10(3) cells/colony was the sensitivity of HCT-8 cells to the antimetabolite comparable to that obtained in HS or dialyzed FBS (ED50 values in the range of 0.01 microM). MTX protection experiments indicated that even very small concentrations of thymidine and hypoxanthine together were sufficient to reproduce the pattern of sensitivity to MTX observed under culture conditions with undialyzed FBS. We conclude that for a proper evaluation of MTX cytotoxicity in clonogenic assays, dialyzed FBS and thymidine-less media should be employed; if native FBS is an absolute requirement for growth, only very large colonies (at least 10 cell divisions) should be scored.

Adenocarcinoma↗