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PubMed2004

Estimation of ultrasound wave aberration with signals from random scatterers.

A method for estimating waveform aberration from random scatterers in medical ultrasound imaging has been derived and its properties investigated using two-dimensional simulations. The method uses a weighted and modified cross-spectrum in order to estimate arrival time and amplitude fluctuations from received signals. The arrival time and amplitude fluctuations were used in a time delay, and a time delay and amplitude aberration correction filter, for evaluation of the retransmitted aberration corrected signal. Different types of aberration have been used in this study. First, aberration was concentrated on the plane of the transmitting/receiving array. Second, aberration was generated with a distributed aberrator. Both conditions emulated aberration from the human abdominal wall. Results show that for the concentrated aberrator, arrival time and amplitude fluctuations were estimated in close agreement with reference values. The reference values were obtained from simulations with a point source in the focal point of the array. Correction of the transmitted signal with a time delay, and a time delay and amplitude filter produced approximately equal correction as with point source estimates. For the distributed aberrator, the estimator performance degraded significantly. Arrival time and amplitude fluctuations deviated from reference values, leading to a limited correction of the retransmitted signal.

Abdominal Wall↗
PubMed1991

CBF measured by Xe-CT: approach to analysis and normal values.

Normal reference values and a practical approach to CBF analysis are needed for routine clinical analysis and interpretation of xenon-enhanced computed tomography (CT) CBF studies. We measured CBF in 67 normal individuals with the GE 9800 CT scanner adapted for CBF imaging with stable Xe. CBF values for vascular territories were systematically analyzed using the clustering of contiguous 2-cm circular regions of interest (ROIs) placed within the cortical mantle and basal ganglia. Mixed cortical flows averaged 51 +/- 10ml.100g-1.min-1. High and low flow compartments, sampled by placing 5-mm circular ROIs in regions containing the highest and lowest flow values in each hemisphere, averaged 84 +/- 14 and 20 +/- 5 ml.100 g-1.min-1, respectively. Mixed cortical flow values as well as values within the high flow compartment demonstrated significant decline with age; however, there were no significant age-related changes in the low flow compartment. The clustering of systematically placed cortical and subcortical ROIs has provided a normative data base for Xe-CT CBF and a flexible and uncomplicated method for the analysis of CBF maps generated by Xe-enhanced CT.

Adult↗
PubMed1993

Danish external quality assessment scheme: an interlaboratory comparison study on lead, cadmium and chromium in lyophilized human blood concentrate.

A Danish External Quality Assessment Scheme (EQAS) was carried out by the Danish National Institute of Occupational Health during the period 1988-1992. The scheme was implemented for 29 international laboratories from 15 countries assaying lead, cadmium, and chromium in human blood to ascertain the systematic error and uncertainty of the analytical methods. In the survey the quality control material AMI B701-B705, based on lyophilized human whole-blood concentrate, were used. As an estimate of the true values the reference values used in this evaluation were (a) the computed values, i.e., sum of the basal and spiked trace element concentration, and (b) the consensus values normally used in the Danish EQAS. This international evaluation of lead, cadmium, and chromium in human blood demonstrated that the use of lyophilized human blood concentrate quality control materials combined with this scheme is valuable in estimating the systematic error and the uncertainty of the analytical methods. For evaluating analytical performance, the computed values were preferable to the consensus values for lead and cadmium in human blood. Due to analytical difficulties suitable reference values were not established for chromium in blood. The study revealed analytical difficulties for cadmium and chromium in human blood. The assessment of laboratories according to established performance indexes indicates that few laboratories can maintain these performance indexes.

Cadmium↗
PubMed1984

Clinical responsiveness to laboratory results.

Digoxin prescriptions written by physicians after obtaining digoxin assay results were reviewed for 100 patients in order to study aspects of experts' interpretation of test results; also 77 pathologists' interpretations of serum digoxin assay results and glucose tolerance curves were studied. There was agreement on the interpretation of only some extreme test result values. Borderline values evoked a mixture of opinions. Responsiveness to result values was measured in terms of the extent of agreement among interpreters and was found to depend on the amount of deviation of the result value from referent values. This is consistent with the idea that the attention given to tests varies with the result value according to its perceived contribution toward reducing clinical error rates. Thus, there is no requirement for unusual analytic precision near referent values, as clinicians respond to results with more skill than anticipated.

Aged↗
PubMed1998

Clinical and statistical evaluation of self-monitoring blood glucose meters.

OBJECTIVE: Our objective was to compare statistical and clinical methods for the evaluation of five self-monitoring blood glucose (SMBG) meters. RESEARCH DESIGN AND METHODS: Two successive capillary blood glucose measurements were performed, and a simultaneous laboratory venous glucose measurement was used as the reference value. Accuracy was studied by comparing each of the two successive meter values with the reference value by 1) a Spearman's correlation test, 2) a Wilcoxon's paired test, 3) the percentage of values within the 10% interval of the reference value according to the American Diabetes Association consensus statement, and 4) the error grid analysis. RESULTS: The first two methods did not discriminate between the SMBG systems: r was >0.92 for the five meters, and a significant difference between the meter and reference values was found for all but one meter. The two other methods allowed classification of the devices into three groups according to their accuracy: good (two meters), acceptable (two meters), and unacceptable (one meter). These two methods gave consistent results and both had a good reproducibility, because the classification was similar for the two successive measurements. CONCLUSIONS: Both the Spearman's and Wilcoxon's paired tests, although commonly used, are inappropriate to evaluate SMBG systems. The percentage of SMBG values within the +/-10% interval and the error grid analysis are more accurate, because they consistently classified the five glucose meters tested in our study with a high degree of reproducibility.

Adult↗
PubMed2005

Age-related variations in acylcarnitine and free carnitine concentrations measured by tandem mass spectrometry.

BACKGROUND: The acylcarnitine profiles obtained from dried blood spots on "Guthrie cards" have been widely used for the diagnosis and follow-up of children suspected of carrying an inherited error of metabolism, but little attention has been paid to potential age-related variations in the reference values. In this study, we evaluated the variations in free carnitine and acylcarnitine concentrations with age, as measured by tandem mass spectrometry. METHODS: Filter-paper blood spots were collected from 433 healthy individuals over a period of 17 months. Eight age groups were defined: cord blood, 3-6 days (control group), 15-55 days, 2-18 months, 19-59 months, 5-10 years, 11-17 years, and 18-54 years. Free carnitine and acylcarnitines were measured for each individual. Mean values were calculated for each age group and compared with those for the control group. RESULTS: Free carnitine was significantly higher in older children than in newborns (P <0.05), but the concentrations of several acylcarnitines tended to be significantly lower in cord blood and in groups of older children than in the control group. Only minor sex-related differences were observed. CONCLUSION: Although the risk of underdiagnosis of fatty acid oxidation disorders with the use of newborn values as reference can be considered as small, in some circumstances the use of age-related reference values may have a potential impact on the diagnosis and management of inherited errors of metabolism.

Adolescent↗
PubMed2000

Reference spirometric values for healthy lifetime nonsmokers in Thailand.

The normal spirometric reference values for Thai people are still not yet available. The aim of this study was to establish standard spirometric equations for Thai people. Subjects 10 years of age and over were selected and their demographic distributions represented that of the population of the whole country. Inclusion criteria were strictly lifetime nonsmokers, no history of chronic cardiopulmonary disease (using a modified ATS--DLD 78 respiratory adult questionnaire), normal standard chest radiograph and unremarkable physical examination. They had to be without respiratory symptoms at the time of the study. Spirometric values were obtained by 5 turbine system 'Pony graphic' (Cosmed, Italy) spirometers which met ATS recommendations. A normal group of 2299 women and 1655 men were selected. Regression analyses using sex, height and age as independent variables were used to provide equations for predicted values. The results were: [table: see text] FVC and FEV1 from this study are close to the Chinese but are 8-20 per cent lower than the Caucasians. These predicted equations are recommended to be used for future reference values in the Thai population.

Adolescent↗
PubMed1995

Reference materials and reference measurement systems in laboratory medicine. Transfer of values to reference materials.

For concentration values assigned to reference and proficiency testing materials, and to patient samples, to be traceable to those in recognised, authoritative reference materials, the value must be transferred from these materials by precise methods. The intent of this document is to outline guidelines for transfer of values from a higher to a lower level reference material, e.g. from primary to secondary4) and from secondary to working reference materials. The guidelines are intentionally broad and relatively non-specific; they may still require revision for specific analytes.

Chemistry, Clinical↗
PubMed1999

Evaluation of hyperhomocysteinaemia in children with stroke.

Hyperhomocysteinaemia is associated with an increased risk of arterial vascular disease and thrombosis in adults. Our aim was to study the association of hyperhomocysteinaemia and stroke in children. Since some patients who had suffered a stroke developed seizures and received treatment with anti-epileptic (antifolate) drugs, we also examined the possible interaction between anti-epileptic drugs and hyperhomocysteinaemia. Plasma total homocysteine was measured in 68 children with stroke (23 of the 68 were taking anti-epileptic drugs) and 100 children undergoing anti-epileptic treatment but without history of stroke, and we compared the values with our reference values for similar ages (n = 195). Total homocysteine was determined by high profile liquid chromatography with fluorescence detection. Hyperhomocysteinaemia was defined as a homocysteine concentration above the 95th percentile for the reference values. Significant differences were found in total homocysteine values of children with stroke and those taking anti-epileptic drugs compared with our reference values for similar ages, except for the adolescent group. Total homocysteine values above the 95th percentile for the reference values were found in 36% of patients with stroke and 28% of children on anti-epileptic treatment. Total homocysteine concentrations in the 23 patients with both stroke and anti-epileptic drug treatment were similar to those of untreated patients with stroke in all age groups. In summary, systematic screening for hyperhomocysteinaemia should be included in the protocol to investigate the aetiology of stroke, even in paediatrics. Anti-epileptic treatment in children with stroke may be responsible for the mild hyperhomocysteinaemia observed in some of them. A dietary supplement of folate may be of benefit in children with stroke and in patients taking anti-epileptic drugs.

Adolescent↗
PubMed1997

Within-subject variation of carcinoembryonic antigen in colorectal cancer -- application of reference of change values and individual reference ranges to patient follow-up.

Dynamic interpretation of results is an alternative approach to the conventional cut-off procedure. Reference change limit is a valuable reference point to interpret dynamically tumour marker values when only very few serial results can be obtained from a patient after treatment. In this paper, a reference change limit of 2.0 microg/l was estimated for carcinoembryonic antigen in patients with complete remission of colorectal cancer. This figure means that a difference greater than 2.0 microg/l has at least a chance of being statistically significant (at 0.05 probability). As complementary information to the reference change limits, with more than four successive results, a simple time series model can be used to obtain predictive limits for the next observation.

Adenocarcinoma↗
PubMed1992

[Present status and problems of the normal values (clinical reference range) of the laboratory tests--results of a questionnaire survey in university hospitals in Japan].

The normal values (clinical references range) of the laboratory tests differs among hospitals due to the differences in: (1) the kinds of instruments and reagents used, (2) how the population for study was selected and the size of the population was, (3) when the specimens were taken, (4) how they were stored until use, and (5) how the data obtained were calculated and (6) who evaluated the results. In this study, questionnaires regarding the above-mentioned points were sent to the heads of the clinical laboratories in 80 university hospitals in Japan. Answers were received from 71 laboratories (the rate of recovery was 88.8%). The normal range of potassium, uric acid, total cholesterol, enzyme activities [ALP, LDH, CHE, AST (GOT) and ALT (GPT)] in the university hospitals in Japan varied. It is not ideal to use different reference values in different hospitals. However, it is impossible to prepare a standard manual to obtain the normal range at present. When the inter-hospital differences become small enough to obtain one normal range for the Japanese peoples, a standard manual for normal values should be made.

Cholesterol↗
PubMed2004

Spirometry values in adults in northern Finland.

OBJECTIVES: If reference values do not accurately reflect the distribution of lung function in the population, the interpretation of spirometry results may be incorrect. Differences in lung function exist between populations, which supports the use of local reference values. In Finland, the national reference values for spirometry are currently in use. The aim of this study was to assess the correlation between measured spirometric values from healthy adults and the reference values used in Finland. METHODS: In the present population-based study, spirometry results were assessed in healthy adults aged 21 to 70 years in northern Finland. After exclusions for any chronic pulmonary disease or symptom, 206 men and 215 women remained in the group. We calculated regression equations for spirometric reference values in adults and compared these with European recommendations, and with the reference values currently used in Finland. RESULTS: These comparisons revealed large differences. The linear models do not take into account the physiological changes in both young and old adults and, thus, the reference values calculated according to the European recommendations differed from the real measured results at both ends of the 20- to 70-year age scale. Moreover, values from the logarithmic Finnish reference equations also diverged from our measurements; the differences were largest in subjects younger than 30, and in elderly men. CONCLUSION: Differences between populations and reference equations make international comparisons difficult, and divergence between reference values and real results may lead to incorrect clinical interpretation.

Adult↗
PubMed1993

Biological monitoring of occupational pesticides exposure.

Two kinds of measurement: (1) enzyme activities in blood, and (2) unchanged pesticides and their metabolites in urine or blood have been used in biological monitoring for assessing exposure to pesticides. The assays of acetylcholinesterase (AChE) activity in whole blood and erythrocytes are mainly applied to estimate inhibition by organophosphates (OPs) and carbamates. A level at 70% of an individual's baseline or of a mean population AChE activity has been recommended as a reference value for exposure control. The measurement of lymphocyte "neuropathy target esterase (NTE)" activity in subjects handling axonopathic OPs is mainly for research application. Analytical methods are available for detecting alkylphosphates, carbamates, pyrethroids, chlorinated hydrocarbons, some herbicides and fungicides, chlordimeform, chlorobenzilate, dichloropropene, dinitrocresol and pentochlorophenol or their metabolites in urine or blood. However, due to lack of significant dose-response or dose-effect relationship, the majority of these determinants can only be used as biological exposure indicators to confirm exposure or to estimate internal dose. Further research in developing adequate indicators and methods for biological monitoring of occupational pesticides exposure is needed. Pre-exposure value and/or reference value of relevant indicators are necessary for assessing the degree of exposure and absorption.

Environmental Monitoring↗
PubMed1999

[Human biomonitoring of polychlorinated biphenyls in 130 exposed elementary school children].

In the classroom air on a primary school polychlorinated biphenyls were present in a wide range extending to 10.220 ng/cbm; in a side room even 19.550 ng/cbm were measured. The school was closed down, a flame retardant paint was detected to be the main source of this contamination. 130 differently exposed persons gave blood specimens for measurement of PCB concentrations. Compared with a comparative reference collective of equal age reported by the analysing laboratory, the PCB blood concentrations of 92 actual pupils were even lower. A comparison with five near-representative child collectives of South Germany did not show any obvious difference. The reference values of the German Human Biomonitoring Commission were exceeded by 4 of 92 pupils for PCB 138, by 6 pupils for PCB 153 and by 6 pupils for PCB 180. In a group of 9 teachers and 1 cleaning person the median values of reference collectives of equal age reported by the analysing laboratory were exceeded by 8 persons for PCB 138, 7 persons for PCB 153 and 8 persons for PCB 180. The 95. Percentiles of these reference collectives and the reference values of the German Human Biomonitoring Commission were not exceeded. In bivariate and multiple regression analyses the data of 92 actual pupils showed positive associations between blood levels of PCB and age as well as nursing period, a negative association between PCB blood concentrations and body-mass index and a weak influence by gender (boys had lower blood concentrations). In addition, the results of multiple regression analyses showed (with the exception of the analyses of PCB 180 without controlling for gender) a significant influence of PCB concentrations in indoor air on PCB blood concentrations. This association could not be detected in bivariate analyses, and in comparison to the mentioned main influence variables it was obviously weaker. But basing on the results of the multiple regression analyses one can calculate an increase of PCB blood concentration by 3% multiplicatively if PCB indoor concentrations increase by 1000 ng/cbm.

Air Pollutants↗
PubMed1983

A laboratory reference vaccine to titrate immunogenic activity of antibrucella vaccines in mice.

The number of bacteria (CFU) in spleens of mice fifteen days after a standard intraperitoneal challenge of Brucella abortus, is dependent on vaccinal immune status of mice. From this observation, a control method of vaccinal activity was previously proposed, which classified the responses in relation to fixed reference values. A reference vaccine, a lyophilized formalin-killed bacterial cell suspension of B. melitensis strains H38 was prepared and titrated. From the dose response curve, the quantities giving reference values were calculated and expressed in a Unit system. This vaccine makes possible inter-laboratory comparisons of vaccinal activity, that can be expressed on the Units basis.

Animals↗
PubMed2005

Power function of the reference change value in relation to cut-off points, reference intervals and index of individuality.

The reference change value, defined as RCV = 1.96 x 2(1/2) x(s(I)(2) +s A(2))(1/2), where s(I) is within-subject biological variation and s A is analytical variation, has been used for many years to take clinical decisions in patient monitoring. Furthermore, the index of individuality was defined as II = (s(I)(2) +s(A)(2))(1/2)/s(G) , where s(G) is the between-subject biological variation. This index has been simplified by later authors to s(I)/s(G) and has been used in monitoring situations to determine the utility of population-based reference intervals. Harris stated that when the index of individuality is lower than 0.6, the specific reference interval of the individual - when available - is better than the population-based reference interval. However, if a change within a patient is equivalent to the RCV applied for the significant difference between two measurements, the probability of detecting this change is only 50% (the same probability of missing it). Therefore, to obtain a higher probability of detecting a change by the RCV (e.g., 90%) the interpretation of the index of individuality has to be reconsidered. This contribution compares the power of the RCV to the use of cut-off points and population-based reference intervals. The benefits of the RCV compared to the distance to cut-off point or reference limit are also described in relation to the index of individuality.

Analysis of Variance↗
PubMed1982

A new concept for quality control of clinical laboratory investigations in the light of clinical requirements and based on reference method values.

Quality control is an essential element in clinical laboratory investigations. In the basic programs for quality control used in recent years accuracy control has been carried out through a comparison with method-dependent assigned values. With this system the "accuracy" of results from different laboratories is relative, and comparability is assured only when the laboratories use the same analytical method. Considering the steadily increasing variety of methods and equipment, a meaningful exchange of information in patient care, teaching and research is becoming more and more difficult; but clinical requirements make such an exchange essential. In this paper a new concept for quality control is presented for discussion. In the basic program incorporating the new concept the method-dependent assigned values are replaced by reference method values, which are method-independent. In addition to accuracy control, an ongoing monitoring procedure using a Shewhart control chart is also carried out. The maximum allowable day-to-day imprecision and the maximum allowable deviation from the reference method value are fixed on the basis of clinical requirements. This means that the ratio of biological variation to analytical between-day imprecision should be greater than or equal to 2. If the biological variation is unknown, then the reference interval is used in its place; the quotient, reference interval/analytical between-day imprecision, should then be greater than or equal to 8. The decision limits for the interlaboratory surveys should be fixed in an analogous manner independent of the analytical method. After the introduction of quality control based on the new concept the results from different laboratories would be comparable to the extent dictated by clinical requirements. The main principles underlying the new concept and the effects of using the new approach are presented for discussion, and the reader is invited to submit comments in writing.

Blood Glucose↗