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PubMed1980

Predictive value and efficiency of laboratory testing.

Literature on determining reference values and reference intervals on "normal" or "healthy" individuals is abundant. It is impossible, however, to evaluate a data set of reference values and select a suitable reference interval that will be meaningful for the practice of medicine. The reference interval, no matter how derived statistically, tells us nothing about disease. This is the main reason the concepts of "normal values" have failed us and why "reference values" will prove similarly disappointing. By studying these same constituents in a variety of disease states as well, it will be possible to select "referent values" that will make the test procedure meaningful for diagnostic purposes. In order to obtain meaningful referent values for predicting disease, it is necessary to study not only the "healthy" reference population, but patients with the disease in question, and patients who are free of the disease in question but who have other diseases. Studies of this type are not frequently found for laboratory tests that are in common use today.

Clinical Laboratory Techniques↗

PubMed2004

Analytical quality specifications for common reference intervals.

Interpretation of laboratory test results requires comparison to some type of reference value or reference interval. These comparisons can be cross-sectional (population-based reference interval and cut-off values) or longitudinal (reference change value). Quality specifications for cross-sectional comparison have been established by determining the influence of analytical bias and imprecision on the percentage of the healthy population falling outside the reference limits, when sharing population-based reference intervals in a Gaussian distribution of results. Quality specifications for longitudinal comparisons are equally important and are often overlooked, since less work has been done in this area. Some criteria suggest that a difference between consecutive results designates a true change in a patient health status when the difference is higher than the within-subject biological variation plus the within-laboratory analytical variation. In this chapter we discuss the clinical considerations and laboratory-related factors that must be considered when quality specifications are applied to sharing reference comparisons. Real life experience shows that different analytical methods can produce comparable results when common quality goals are established, and quality can be achieved through a willingness to work together. Within the existing organization, the current specifications for analytical quality and a dedication to quality health care makes it possible to achieve transferability between laboratories within a geographic area.

Clinical Chemistry Tests↗

PubMed2003

Corneal esthesiometry in the healthy horse.

OBJECTIVE: To determine corneal sensitivity in healthy adult horses in order to establish reference values. ANIMALS STUDIED: One hundred eyes of 50 healthy adult horses. PROCEDURE: Corneal sensitivity was determined by evaluating the corneal touch threshold (CTT) in five different corneal regions using a Cochet-Bonnet esthesiometer. RESULTS: Comparing CTT values (in mm filament length) of the five prescribed corneal regions revealed regional variations in corneal sensitivity, with the central region (21.15 +/- 6.23 mm) being the most sensitive, followed by the nasal (20.75 +/- 5.14 mm), temporal (20.70 +/- 5.37 mm), ventral (20.15 +/- 5.88 mm) and dorsal (15.85 +/- 3.70 mm) region. However, differences between the central, nasal, temporal and ventral regions were not statistically significant, whereas the dorsal region was significantly (P < 0.0001) less sensitive compared to the other regions. Division of the horses into three age groups revealed an insignificant decrease in corneal sensitivity with age in the nasal, temporal, ventral and central region, and an insignificant increase with age in the dorsal region. Correlation of corneal sensitivity with age was statistically significant in the central, ventral and temporal region. No statistically significant difference in the CTT was found between left and right eyes and between males and females. CONCLUSIONS: CTT values in 100 eyes of 50 healthy adult horses evaluated with a Cochet-Bonnet esthesiometer generated reference values. Reference values are necessary to determine alterations of corneal sensation accompanying various eye diseases or systemic diseases.

Animals↗

PubMed2003

Relationships of metabolic profiles to milk production and feeding in dairy cows.

The aim of this study was to assess the practicality of the metabolic profile test (MPT) for feeding evaluation in dairy cattle. Stepwise regression analysis was used to evaluate the relationships of MPT to feeding and milk production of 4,679 cows in 343 commercial dairy herds. Significant explanatory variables were determined by forward set-up selection, among the deviated values from the reference values of 10 blood metabolites and body condition score, to predict dependent variables, i.e., milk production and the rate of feeding to nutrient requirements, in each or all lactation stages and the dry period. The milk production model of the all-lactation stage showed the greatest goodness-of-fit (adjusted R(2)=0.214, p<0.0001) with high positive regression coefficients for serum cholesterol, magnesium, urea nitrogen and albumin, and negative for glucose and calcium. In the feeding models, goodness-of-fit of crude protein was relatively high (R(2)=0.072, p<0.0001) with a positive relationship to blood urea nitrogen. Although the other feeding models were low in goodness-of-fit, several significant explanatory variables to feeding were found. All feeding models in the late lactation stage and the dry period, in which the feeding was stable, had greater goodness-of-fit than those in the early lactation stage in which milk production varied. It was concluded that the values which deviated from the reference values for the MPT components could assess milk production and feeding, and the MPT is a practical tool for auxiliary feeding evaluation.

Animal Feed↗

PubMed1993

On the calculation of reference change values, with examples from a long-term study.

Reference change values (sometimes called critical differences) indicate statistically important changes between test values obtained on two occasions. They are commonly computed from the median (or mean) within-subject variance observed in repeated test measurements on a number of subjects. With this computational approach, all observed within-subject variances are assumed to be estimates of a constant true variance, the same for all individuals. Moreover, any possible correlation between successive values is almost always ignored. This simplified methodology differs from the method originally proposed for computing reference change values, which accounts for variability in true variances and for serial correlation. From data obtained from repeated measurements over 2 to 5 years in 72 physically healthy subjects, we computed and compared reference change values in 18 serum analytes, using the simplified method and the originally proposed procedure. Although the original method is more complicated and requires a computer program, we believe that it produces more-reliable reference change values than those obtained by the simplified approach. The former are generally larger, but remain sensitive to clinically important changes in the individual.

Adolescent↗

PubMed1997

Use of dual-energy X-ray absorptiometry for the measurements of small quantities of mineral.

The aim of the study was to assess the precision and the accuracy of whole-body dual-energy X-ray absorptiometry (DXA) measurements of low quantities of mineral. Six stillborn infants were measured three times in order to assess the precision in vivo. Powdered bone tablets were also measured three times separately or in compact groups (0.32-41.7 g of hydroxyapatite) by whole-body DXA. Mean correlation coefficients were 6.85 +/- 5.99 and 6.74 +/- 6.58% in vivo and in vitro, respectively. DXA-based estimates of the tablets were highly correlated with the actual bone mineral content (BMC; r = 0.99, p = 0.0001). The mean difference between DXA values and the reference values was 2.55 +/- 10.93%, but the agreement between DXA results and reference values rose to 3.99 +/- 3.49% for BMC above 10 g. Very small amounts of mineral can be measured by whole-body DXA, but assessment of an infant with a BMC less than 10 g should be made with care.

Absorptiometry, Photon↗

PubMed1994

Mucopolysaccharidoses screening: dimethylmethylene blue versus alcian blue.

The dimethylmethylene blue (DMB)-based screening procedure for mucopolysaccharidosis and the alcian blue (AB)-based procedure both measure glycosaminoglycan (GAG) content directly in urine. We compared the two procedures. Absorbance per microgram of GAG for DMB was 25 times that obtained with AB, resulting in a requirement for 10 times smaller sample volumes for the former. Recoveries of added heparan sulphate for the AB assay in the absence and presence of added protein (2.5 g/L) were comparable (78-95% and 75-111%), as was the case with the DMB assay. Here, recoveries were generally better (94-103% and 96-100%). The coefficient of correlation (CC) between the two methods measured on 86 reference urine samples was 0.861. For mucopolysaccharidosis urines the CC was higher (0.928). Age-dependent reference values were comparable. Performance of the assays was compared by measurement of GAG content in 24 mucopolysaccharidosis urines. Standard deviation scores (measured value minus mean of reference values divided by standard deviation in reference values) and probabilities for classification in the patient group were calculated and compared. Especially for urines from patients with less distinctly increased GAG content (Sanfilippo, Scheie), scores and probabilities were higher with the DMB assay.

Adolescent↗

PubMed2003

Reassessment of von Willebrand factor (VWF), VWF propeptide, factor VIII:C and plasminogen activator inhibitors 1 and 2 during normal pregnancy.

The use of von Willebrand factor [VWF antigen (WF:Ag)] measurement as a marker of endothelial cell activation for monitoring hypertensive pregnancies is limited by the poor definition of reference values. We reassessed these reference values using different assays, and those of the propeptide (VWF:Ag II) and factor VIII coagulant activity (factor VIII:C), in a large population of normal pregnancies, at 3-week intervals of gestational age. Plasminogen activator inhibitors (PAI-1 and PAI-2) were measured in parallel. Blood was collected at single time points between 12 weeks and delivery in 306 women undergoing normal singleton pregnancy. For clinical purposes, the VWF:Ag reference values were assay independent and the influence of ABO blood group on VWF:Ag or factor VIII:c was found to be limited during the third trimester. VWF:Ag II was not influenced by the ABO blood group. The ratio, VWF:Ag/factor VIII:C was close to 1.0 throughout pregnancy. In contrast, VWF:Ag II increased more slowly than VWF:Ag and the ratio of VWF:Ag II to VWF:Ag in plasma decreased from 1.00 to 0.5 at term. PAI-1 and PAI-2 increased with gestational age, but PAI-2 decreased during the last 2 weeks, indicating physiological placental regression at the very end of pregnancy.

Factor VIII↗

PubMed2006

Accuracy, reproducibility, and comparability of Doppler tissue imaging by two high-end ultrasound systems.

INTRODUCTION: Doppler tissue imaging is a new technology for quantitative evaluation of myocardial motion and contractility, and is available in several ultrasound systems. This study evaluates the comparability, accuracy, and reproducibility of measurements of velocity, strain rate, and strain by two high-end ultrasound systems. METHODS: Accuracy was assessed by imaging a tissue-mimicking gelatin phantom, and the comparability of measurements in the right ventricular free wall and interventricular septum was assessed in 20 healthy participants. Reproducibility was evaluated by repeated recordings in vitro and in a random subset of patients. RESULTS: In vitro, a high degree of accuracy was found in both systems, with one system measuring slightly lower values than the reference values (mean difference 0.35 +/- 0.18 cm/s, P < .001). Values higher than the reference values were measured by both systems for strain and strain rate. In vivo, no systematic differences in measured velocities, strain rate, and strain were found; however, wide limits of agreement were seen for strain and strain rate. Measurements of tissue velocity, strain, and strain rate were well reproducible, nevertheless wide variation was found in both systems (coefficient of variation = 9%-19%). CONCLUSION: For clinical purposes, both systems have sufficient accuracy for measurements of tissue velocity. The variation in measurements of strain rate and strain by Doppler tissue imaging should be taken into account when designing studies using this new technology. Approaches to potentially reduce this variation should be addressed in future studies.

Echocardiography, Doppler↗

PubMed1996

Determination of reference method values by isotope dilution-gas chromatography/mass spectrometry: a five years' experience of two European Reference Laboratories.

We report on the cooperation of two European Reference Laboratories for the determination of reference method values in serum based materials intended for use in internal accuracy control and external quality assessment. Reference method values were determined by isotope dilution-gas chromatography/mass spectrometry for aldosterone, cortisol, oestradiol-17 beta, progesterone, testosterone, thyroxine, theophylline, cholesterol, creatinine, glucose, total triacylglycerols and uric acid. All determinations were done in parallel in the two laboratories, independently and within certain time constraints. The general measurement design consisted of duplicate measurement of each sample on three different occasions. In each laboratory, rigorous internal quality control was performed according to predefined analytical quality specifications. This was done using certified reference materials. If not available, control materials targeted before by the two laboratories were utilized. Here we present the results of the cooperation during five years. We discuss the precision and accuracy achieved, the between-laboratory agreement and the total analytical error. For the hormones and theophylline, the mean overall coefficient of variation for both laboratories (calculated from the measurements on three days) was always < 2%, for the substrates < 1%. For all substances, the method bias (estimated from several measurement series over the five years) was < 1%, and the average deviation of the results between the two laboratories was < 1.2%. The maximum total analytical error was in all cases < 3%. These data demonstrate that current reference methodology is able to guarantee a stable level of high quality of performance, and that reference laboratories of today are capable of providing, in due time, adequate service in the framework of accuracy-based harmonization of methods in routine laboratory medicine.

Aldosterone↗

PubMed1999

Indirect reference limits estimated from patients' results by three mathematical procedures.

Presently, only a few clinical laboratories produce their own reference values, while the great majority use reference intervals reported in the literature. An alternative to this unsatisfactory situation is to estimate indirect reference limits by means of mathematical/statistical procedures from patients' results obtained routinely in the laboratory. The procedures of Bhattacharya (A simple method of resolution of a distribution into Gaussian components. Biometrics 1967;23:115-135) Martin et al. (Reference values based on populations accessible to hospitals. In: Gräsbeck R, Alström T, editors. Reference Values in Laboratory Medicine. Chischester: Wiley, 1981:233-262) and Kairisto et al. (Generation of reference values for cardiac enzymes from hospital admission laboratory data. Eur J Clin Chem Clin Biochem 1994;32:789-796) were applied to 14 biochemical quantities. In order to verify these procedures, the indirect reference limits obtained from patients' results were validated by statistical comparison with reference limits estimated from a reference sample according to recommendations of the International Federation of Clinical Chemistry (IFCC). Calculated indirect reference limits for most quantities studied were reliable, but indirect reference limits for bilirubins and potassium ion substance concentrations, alanine aminotransferase, and aspartate aminotransferase catalytic concentrations in serum were not suitable. We conclude that indirect reference limits can be obtained from patients' results by all procedures studied when skewness and kurtosis of mixed distribution are not too large, but other factors also seem to have an influence on the reliability of these procedures.

Adult↗

PubMed2004

Validation of real-time three-dimensional echocardiography for quantifying left and right ventricular volumes: an experimental study.

BACKGROUND: Assessment of the left ventricular (LV) and the right ventricular (RV) volumes and their functions is important for prognostic prediction and clinical decision making. We compared the accuracy for quantifying the LV and the RV volumes in vitro between conventional two-dimensional echocardiography (2DE) and real-time three-dimensional echocardiography (RT3DE). METHODS: The volumes of 37 rubber-models (10 regularly shaped to simulate normal LV, 7 shaped to simulate LV with symmetric aneurysm, 8 shaped to simulate LV with asymmetric aneurysm, and 12 irregularly shaped to simulate normal RV) and 10 excised canine hearts were measured by RT3DE and 2DE. On RT3DE "full volume" imaging, the inner-surfaces of the rubber-models and canine LV and RV were outlined and the volumes were measured using 2-, 4-, 8- and 16-plane methods with the RT3DE analysis software. On 2DE imaging, the volumes were measured by the Simpson method. The LV and RV volumes measured by drained water were served as reference values, with which we compared RT3DE and 2DE data. RESULTS: In rubber models mimicking normal LV and LV with symmetric aneurysms, RT3DE results were strongly correlated with reference values (r = 0.795 - 0.998) and there was a good correlation between 2DE estimates and reference values (r = 0.715 - 0.729). There were no significant differences between RT3DE estimates, 2DE results and reference values (P > 0.05). In rubber models mimicking the RV and LV with asymmetric aneurysm, RT3DE strongly correlated with reference values (r = 0.765 - 0.988), but 2DE weakly correlated with reference values (r = 0.518 - 0.592). There were no differences between RT3DE and reference values (P > 0.05), but a significant difference between 2DE and reference values occurred (P < 0.05). For excised canine hearts, there was a strong correlation between RT3DE and reference values (r = 0.728 - 0.914), while 2DE showed a less obvious correlation (r = 0.502 - 0.615). Again, there were no significant differences between RT3DE and reference values (P > 0.05), but there was a significant difference between 2DE and reference values (P < 0.05). CONCLUSIONS: RT3DE can accurately quantify LV and RV volumes and provides a new tool to evaluate LV and RV function. For LV and RV measurements by RT3DE, 8-plane strategy is the optimum choice for accuracy and convenience.

Animals↗

PubMed1995

Bone mineral density measurement by quantitative computed tomography in a normal Turkish population.

PURPOSE: To observe the trabecular and cortical bone mineral density values of a normal Turkish population, to examine the effect of age in males, and age and duration of menopause in a female population on bone mineral density. Also to compare Turkish population bone mineral density values with the reference values in developed countries. MATERIALS AND METHODS: Trabecular and cortical bone mineral densities were measured by the quantitative CT method in 255 (110 male and 145 female) normal cases. RESULTS: According to the linear regression test results, loss of bone mineral density per year was 1.97 mg/ml and 2.09 mg/ml for females and 1.37 mg/ml and 1.04 mg/ml for males in the trabecular and cortical bone compartments, respectively. A 70-year-old female loses 56.7% and 31.3% of the bone mass at 20 years of age for the trabecular and cortical compartments, respectively. These ratios were 41% and 16.1% for the male population. Most loss in bone mass was observed in the premenopausal and early postmenopausal period. In the postmenopausal period, duration of menopause had more effect on bone mass than age. Loss of trabecular bone mass per year in the postmenopausal period was 2.36 mg/ml and 2.84 mg/ml with respect to age and duration of menopause, respectively. CONCLUSIONS: Quantitative CT is a valuable method to determine bone mass because it allows to detect bone mass of trabecular and cortical bone separately. Loss in trabecular bone was found to be higher than in cortical bone for both sexes, while overall bone loss was higher in females. Rate of loss increases in the menopause period. Duration of menopause had more effect on bone mass than age. Bone mineral density values in Turkey were similar to reference values of western countries.

Adolescent↗

PubMed2001

IFCC Reference Measurement Procedure for Substance Concentration Determination of Total Carbon Dioxide in Blood, Plasma or Serum. International Federation of Clinical Chemistry and Laboratory Medicine.

A reference measurement procedure for substance concentration determination of total CO2 in blood, plasma (the anticoagulant is usually heparin) or serum is described. The document covers the principle of the method, the materials and equipment needed and essential aspects of the procedure. The substance concentration of total CO2 in blood, plasma or serum is accurately determined and therefore this procedure is recommended for assigning reference values to reference materials and for blood gas quality assurance in laboratories and by manufacturers of blood gas equipment.

Acid-Base Equilibrium↗

PubMed1984

Excessive consumption of alcohol in men as a biological influence factor in clinical laboratory investigations.

It is known that excessive alcohol consumption leads to changes in clinical chemical and haematological parameters that are reversed to a greater or lesser degree after alcohol consumption ceases. Such factors that lead to changes in vivo in the parameters studied are termed biological influence factors. In the study reported here the biological influence factor "excessive alcohol consumption" was assessed in its most severe form, namely alcoholism. To this end 24 clinical chemical parameters and 8 haematological parameters were studied in 82 male alcoholics. The diagnoses of alcohol abuse and alcoholism were made on the basis of the Munich Alcoholism Test (MALT) and the information obtained in the following standardized interviews and examinations: past history, an alcohol questionnaire, general physical examination and neurological examination. All forms were filled in completely. All steps in the clinical laboratory investigations were standardized, and all were subject to ongoing reliability control. In the comparison of the analytical results for the alcoholics with reference intervals for healthy persons (normal ranges) the following alterations were found, the percentage of the alcoholics being given in parentheses. (Table: see text) Furthermore, the result was below the location parameter of the reference sample group for: Urea (80%) Thus excessive alcohol consumption is clearly a biological influence factor that must be taken into consideration in the medical assessment of analytical results for numerous clinical chemical and haematological parameters. In determining reference values and reference intervals for the transverse assessment of analytical results for these parameters it is therefore absolutely essential that subjects with excessive alcohol consumption be excluded from the reference sample group. According to the present data, alcoholism can be neither detected nor excluded by evaluating a single parameter, i.e. on the basis of only one clinical chemical finding.

Adult↗

PubMedDate not supplied

[Prognostic significance of the cholesterol level in the blood of healthy subjects].

The paper describes a new approach to the formation of "normal" (reference) values: the reference group is to be formed from the subjects in good health condition at the time of the first and repeated (say, five years later) examinations; the reference group cannot include people developing chronic diseases within this time interval.

Adult↗

PubMed1980

[Selection of a statistical model for the evaluation of the reliability of the results of toxicological analyses. II. Selection of our statistical model for the evaluation].

Part II presents a statistical model devised by the authors for evaluating toxicological analyses results. The model includes: 1. Establishment of a reference value, basing on our own measurements taken by two independent analytical methods. 2. Selection of laboratories -- basing on the deviation of the obtained values from reference ones. 3. On consideration of variance analysis, t-student's test and differences test, subsequent quality controls and particular laboratories have been evaluated.

Analysis of Variance↗

PubMed1990

Incomplete virilization and subclinical mineralocorticoid excess in a boy with partial 17,20-desmolase/17 alpha-hydroxylase deficiency.

A 17-year-old boy is described with impaired virilization and subclinical mineralocorticoid excess owing to combined 17,20-desmolase/17 alpha-hydroxylase deficiency. His basal plasma progesterone was 20.9 nmol/l (reference value 0.50-1.88), 17-hydroxyprogesterone 21.3 nmol/l (reference value 3.05-4.84), testosterone 6.85 nmol/l (reference value 14.1-22.0), and his excretion of tetrahydro-11-deoxycorticosterone 11.8 mumol/24 h (reference value 1.0-1.5). The differential effects of this combined enzyme deficiency on adrenal and testicular function were studied by ACTH stimulation, dexamethasone suppression, hCG stimulation, and suppression treatment with testosterone.

Adolescent↗