Mitochondrial cytochrome b DNA sequence variation of Atlantic cod, Gadus morhua, from the Baltic and the White Seas

We studied sequence variation of a fragment of the mitochondrial cytochrome b gene using polymerase chain reaction (PCR) and direct sequencing of 109 Atlantic cod (Gadus morhua) from the Baltic and 19 cod from the White Sea. Eight nucleotide substitutions define 12 haplotypes differing from each other by one to six substitutions. All mutations are at silent sites and thus neutral to selection arising from protein action. Frequencies of four common haplotypes are 6%-57% and haplotype diversity is 0.64 +/- 0.031. Testing for neutral theory predictions reveals no departure from neutrality. The Baltic shares its haplotypes with distant localities in the Atlantic but differs in frequency. Within the Baltic none of the variation is explained by geographic location with an AMOVA. Temporal changes of haplotype frequencies of up to 50% are observed between sampling years and yearclasses. A potential confounding of temporal and microspatial variation cannot be excluded due to limited sample size.

Effect of anticoagulant therapy on the hypercoagulable state in patients carrying the factor V Arg506Gln mutation

Resistance to activated protein C, caused by a single point mutation in the factor V gene (Arg506Gln or FV Leiden), is the most prevalent single risk factor associated with venous thromboembolic disease. The aim of this study was to investigate the effectiveness of standard oral anticoagulant therapy (OAT) in patients with the Arg506Gln mutation compared with a matched control group. The study compared selected variables in 27 patients carrying the Arg506Gln mutation with 27 sex- and age-matched controls in steady state oral anticoagulant treatment (OAT). The study showed that similar doses of vitamin K antagonists in carriers and noncarriers suppress and generate a uniform distribution of coagulation markers in steady state OAT. Thus, it seems that OAT with standard treatment doses is just as effective in patients with the Arg506Gln mutation as in comparable controls without the mutation.

The effect of short-term cortisol changes on growth hormone responses to the pyridostigmine-growth-hormone-releasing-hormone test in healthy adults and patients with suspected growth hormone deficiency

BACKGROUND AND AIMS

The interaction between cortisol and growth hormone (GH)-levels may significantly influence GH-responses to a stimulation test. In order to systematically analyse the interaction in a paired design, it is necessary to use a test, which has been proven safe and reliable such as the pyridostigmine-growth-hormone-releasing-hormone (PD-GHRH) test. Three groups of subjects with a different GH-secretory capacity were included.

STUDY A

Eight healthy adults were tested seven times, once with placebo throughout the examination and six times with the PD-GHRH test following no glucocorticoid pretreatment, pretreatment with hydrocortisone (HC) (30 mg/day and 80 mg/day for 1 and 3 days) or pretreatment with 15 mg prednisolone for 1 day. HC (80 mg/day for 1 day) in combination with PD significantly stimulated GH-levels compared to PD alone, 18.9 mU/l +/- 6.1 vs 3.0 mU/l +/- 0.8 (P < 0.05). However, peak GH-responses to PD in combination with GHRH were reduced during HC (80 mg/day for 1 day) compared to no glucocorticoid pretreatment in all healthy adults. Conventional HC therapy (30 mg/day for 1 and 3 days) did not significantly affect peak GH-responses.

STUDY B

16 patients with suspected GH-deficiency (GHD) (seven with known ACTH-deficiency and nine with an intact pituitary-adrenal axis) were tested five times with the PD-GHRH test following no pretreatment or pretreatment with HC (30 mg/day and 80 mg/day for 1 and 3 days). Peak GH-responses were not significantly affected by conventional HC therapy (30 mg/day for 1 and 3 days). However, peak GH-responses to PD in combination with GHRH were reduced during HC (80 mg/day for 1 day) compared to no glucocorticoid pretreatment in all patients. Short-term hypocortisolism did not significantly affect peak GH-responses.

CONCLUSION

The GH-responses to a PD-GHRH test were reduced in all individuals during acute stress-appropriate cortisol levels and the percentage reduction in GH-levels was independent of the GH-secretory capacity. Clinically, we found that peak GH-responses were not significantly affected by a short break in conventional HC therapy nor by conventional HC therapy itself. However, our results also demonstrated that a GH-stimulation test should not be performed on patients, suffering from acute stress.

Methodological aspects of measuring human skeletal muscle electrolyte content and ouabain binding capacity

The aim of the study was to evaluate the use of freeze-dried and dissected small muscle biopsy specimens ("dry") for the determination of human muscle electrolyte content and ouabain binding capacity, compared with an easier method, without this freeze-drying step ("wet"). Freeze-drying and dissection of muscle biopsy specimens reduced the variation in the determination of muscle potassium and magnesium content. The total coefficient of variation was 8.6% in the dry determination of muscle potassium content and 13.5% in the wet determination (P < 0.05). In the determination of muscle magnesium content, the total coefficient of variation was 7.4% in the dry determination and 13.7% when determined wet (P < 0.005). Muscle sodium content had a very large coefficient of variation, independent of the method used. The content of dry solids was too high in biopsies which were incubated in Tris-vanadate buffer (31.9%), compared to biopsies which were not incubated in Tris-vanadate buffer (24.9%, P < 0.001). Hereby, the measured ouabain binding capacity became too high when measured wet. In conclusion, muscle electrolyte content and ouabain binding capacity should be determined after drying and microdissection of the biopsies, because this method confers the least variation and the highest accuracy.

Evaluation of growth hormone assays using ratio plots

To permit comparison between growth hormone (GH) results obtained using the Pharmacia polyclonal assay and the Delfia monoclonal assay, we used both methods to measure GH concentrations in peak GH responses to the pyridostigmine-growth-hormone-releasing-hormone (PD-GHRH) test and in unstimulated samples from 40 healthy adults and 31 patients with suspected GH deficiency. Ratio plots were used for the comparison, and acceptability criteria were based on inherent analytical imprecision and on analytical quality specifications. The mean ratio (r; Pharmacia/Delfia) for the peak GH responses in 40 healthy adults was calculated to be 1.59, and the 95% prediction interval for ratios fulfilling the imprecision criterion was applied. For GH values >1 mIU/L, the peak and unstimulated GH ratios in healthy adults and patients were within the 95% prediction interval, and fulfilled the biological criterion as well. Therefore, the conversion factor of 1.59 is applicable for the evaluation of GH-stimulation tests.

Biological variation of International Normalized Ratio for prothrombin times, and consequences in monitoring oral anticoagulant therapy: computer simulation of serial measurements with goal-setting for analytical quality

Oral anticoagulant therapy (OAT) has a well-established efficacy in prophylaxis and treatment of thromboembolic disorders. Because complications are related to intensity of OAT, optimal control of treatment is mandatory. In studies of OAT, as many as 30% of International Normalized Ratio (INR) measurements for prothrombin times fall outside the therapeutic interval. Preanalytical, analytical, and biological variation all contribute to this. Computer simulations of serial INR measurements were performed for various assumed in-treatment setpoints within the therapeutic interval INR 2.0-3.0 and for an "in-treatment within-subject variation" (CV) of 10.1%. Results are presented in difference plots with therapeutic intervals and critical differences. If the in-treatment setpoint is mid-interval (INR = 2.5), only 5% of simulated INR values fall outside the therapeutic interval. Setpoints deviating from the mid-interval and increases in the in-treatment within-subject variation considerably increase the number of observations outside the therapeutic interval and the critical differences. In conclusion, random variation, biological or analytical, and setpoints (targets) deviating from mid-interval explain a substantial number of the INR values outside therapeutic intervals observed in clinical studies. Analytical imprecision should be kept < 5% and analytical bias < +/- 0.2 INR.

Evaluation of a near-patient test for C-reactive protein used in daily routine in primary healthcare by use of difference plots

We have assessed the technical performance and robustness of NycoCard CRP Whole Blood, a near-patient test for C-reactive protein (CRP), when used in realistic daily routine situations in general practice clinics (GPC). Thirteen GPCs participated, five of them with technician staff. From 898 patients, split-sample measurements for CRP were made. Results from GPCs were compared with results from a turbidimetric laboratory method, traceable to international reference preparations (IFCC CRM 470). Results were evaluated in difference plots where the expected distribution, due to an estimated analytical variation, was compared with measured differences. Of all difference points, 91.5% (n = 819) were within a 95% prediction interval based on the imprecision of both methods. Mean bias (95% confidence interval) was -0.3 mg/L (-0.9 to 0.3). No differences in analytic quality were found between GPCs with technician staffs and GPCs without, and between test results obtained within the first and second week, compared with the rest of the study period. We find the test as good when used in GPCs as could be expected from laboratory testing, and consequently robust, which is a necessity for use in routine situations in general practice. General application of difference plots in test evaluations are discussed in detail.

Graphical interpretation of analytical data from comparison of a field method with reference method by use of difference plots

Various viewpoints have been offered regarding the appropriate use of scatter plots or difference plots (bias plots or residual plots) in comparing analytical methods. In many of these discussions it seems the basic concepts of identity (within inherent imprecision) and acceptability based on analytical goals (analytical quality specifications) have been forgotten. With the increasing number of Reference Methods in laboratory medicine, these basic concepts are becoming more important in validation of field methods. Here we describe a simple and effective graphical test of these hypotheses (identity and acceptability) by use of difference plots. These plots display the underlying hypothesis before the measured differences are plotted and allow interpretation of the results according to specific criteria. We further describe simple but effective interpretations of the data, when the hypothesis is not fulfilled, by using two data sets drawn from comparisons of field methods for S-creatinine with a Reference Method for this analyte. The difference plot is a graphical tool with related simple statistics for comparison of a field method with a Reference Method, focusing on (a) identity within the inherent analytical imprecision or (b) acceptability within analytical quality specifications. Calculation of the standard deviation of the differences is an indispensable tool for evaluation of aberrant-sample bias (matrix effects).

Estimates of the sources of variation (variance components) of bioelectric impedance and anthropometric measurements in an epidemiological case-control study of breast cancer

OBJECTIVE

This study investigated the variability of anthropometric measurements and body fat estimated by bioelectric impedance analysis. Subsequently the methods were applied in a case-control study to investigate the association with breast cancer.

DESIGN, SUBJECTS

The study group included 50 consecutive cases and 75 age-matched controls from the same area. The variation was investigated in 50 healthy women from the control group, who were repeatably measured using standardised measurement procedures, and the variation between-subjects, within-subjects, between-observers, and within-observers were estimated.

RESULTS, CONCLUSIONS

The study showed that the variance components between-subjects were 64-99% of the total variance. The variables of skinfold thicknesses were characterised by having the highest relative observer variation and having many unavailable values that were out of the range of the Harpenden callipers. The mean body fat by bioelectric impedance analysis was 31.2%, and the total coefficient of variation 23%, while the variance components related to subject time, observer and measurement were 98.4%, 1.1%, 0.2%, and 0.4%, respectively. The body fat was significantly correlated with the variables of skinfold thicknesses. We decided to exclude the variables of skinfold thicknesses from the case-control study, and for the other variables to measure each subject only at one time by one observer. The case-control part of the study indicated a non-significant increase in body weight in the postmenopausal breast cancer patients (mean difference 3.6 kg; confidence interval from -0.9 kg to 8.0 kg). Similarly the body fat tended to be higher in the breast cancer patients (mean difference 1.2%; confidence interval from -1.6% to 4.0%).

The influence of analytical bias on diagnostic misclassifications

Quality specifications for analytical imprecision and bias based on the state of the art; 'biology' and 'analysis of clinical situations' have been proposed by several scientists. Most interesting is the assessment of 'diagnostic misclassifications' based on direct evaluation of the consequences of analytical bias on the percentage of false positives and false negatives from a clinical decision situation, or based on the percentage of healthy individuals outside each reference limit when common reference intervals are used. With use of graphical or computer simulations assuming increasing (positive or negative) analytical bias, the expected percentage of misclassifications can be estimated- and, for the error for which the outcome (the fraction of misclassifications) is considered unacceptable, the maximum allowable analytical bias can be defined. An overview is given of previous proposals for specification of allowable analytical bias, and new examples are presented: (i) for S-transferrin. an analytical bias of +10% will increase the percentage of healthy individuals with measured concentration values above the upper reference limit from 2.5 to 10% (ii) the percentage of healthy men with concentration values for S-cholesterol above 6.2 mmol/l (240 mg/dl) will vary between 25 and 85% for analytical bias from - 1.0 to +1.0 mmol/l (+/- 16%): (iii) for glycated haemoglobin, two examples are given which illustrate the effect of analytical bias on the risk of retinopathy and so-called 'microalbuminuria' for measured values identical to the target 7.5% and 10.1% glycated haemoglobin, respectively. It is concluded that analytical bias may have significant impact on diagnostic performance, better standardization is needed, and quality specifications for allowable analytical bias should be based on medical usefulness criteria or, if such data are not available, on biological criteria.

Proposed guidelines for the internal quality control of analytical results in the medical laboratory

The factors involved in analytical quality relate to definition of quality, creation of quality, and control of quality, and errors arise from external and internal sources as well as from permanent and variable factors. Further, the two main types of error are classified as systematic and random errors. Internal quality control (IQC) systems can only operate on the variable factors which are related to batch-to-batch variations (external factors) and to the performance in the laboratory (internal factors). In creating an adequate internal control system, several problems are faced: (i) quality of control materials, (ii) types and frequency of possible errors, (iii) number and types of control materials, (iv) number of replicates of the control, (v) probability of error detection, (vi) probability of false rejection, (vii) consequences of reject signals, (viii) trouble-shooting systems, and (ix) prevention of errors among many other conditions. Gaussian distributions of control results are assumed and the statistical control rules are evaluated in relation to probability of false rejections, Pfr, and probability of error detection, Ped, for the different rules. Combinations of low Pfr and high Ped are obtained by combining results from e.g. four measurements of the same control sample by use of mean and range rules. Further, it is not possible to establish a common control system which can be used for all quantities and analytical procedures; on the contrary, each procedure should have its particular efficient IQC system. These aspects are discussed and a number of guidelines for statistical control rules and problem related internal quality control are presented.

Cord blood immunoglobulin E in like-sexed monozygotic and dizygotic twins

Genetic and environmental factors have been implicated in the etiology of atopy and of serum IgE levels. In order to eliminate post-natal environmental influences we measured IgE in cord blood (CB-IgE) from a cohort of unselected, like-sexed twins. IgE determination was performed with a sensitive radioimmunoassay with a detection limit of 0.01 kU/l. Samples with contamination by maternal blood were identified by IgA determination and excluded. CB-IgE was evaluated in 29 monozygotic (MZ) and 28 dizygotic (DZ) twin pairs. The means and variances for IgE values were comparable for MZ and DZ twins when sex was controlled for. Placental anatomy (MZ twins with mono- and dichorial placenta and DZ twins with one or two placentae) had no significant influence on the IgE levels. In an analysis of variance with sub-sampling the among-pair, within-pair and analytical variance components were calculated. The analytical variance was well below the biological variances. Biometrical analysis showed that the best model by Akaike Information Criteria was a model including only additive genetic and non-shared environmental factors. With this model the heritability estimate was 0.8. These data suggest that the majority of the variation in CB-IgE is accounted for by genetic factors, but a substantial effect of a common environment cannot be excluded with the present sample size.

Characterization and classification of external quality assessment schemes (EQA) according to objectives such as evaluation of method and participant bias and standard deviation. External Quality Assessment (EQA) Working Group A on Analytical Goals in Laboratory Medicine

Within the scope of this paper, the Working Group has attempted to place external quality assessment (EQA) within the whole context of quality management in laboratory medicine. First, the objectives of EQA schemes are defined and current EQA schemes evaluated. In most schemes, the objectives are not defined a priori and do not allow the definition of the origin of unacceptable individual results from participants. There is an ongoing trend for making traditional EQA schemes more interesting for the participants. Analysis of the factors involved in analytical quality allow the definition of the essential analytical tasks of educational EQA schemes. Beside these quality control tasks, educational EQA also includes quality assurance elements. EQA today has not only an important role to play in the assessment of each participant's performance but also in the assessment of the method. Efficiency of the schemes and educational impact can be improved by appropriate scheme designs according to objectives. After this theoretical approach, some practical examples of problem related EQA designs are given.

Consensus of a group of professional societies and diagnostic companies on guidelines for interim reference ranges for 14 proteins in serum based on the standardization against the IFCC/BCR/CAP Reference Material (CRM 470). International Federation of Clinical Chemistry. Community Bureau of Reference of the Commission of the European Communities. College of American Pathologists

The release in 1993 of a new reference material for serum proteins, CRM 470/RPPHS 5 has given rise to a great improvement in the between-laboratory variability of serum protein measurements worldwide. Conversion to the new reference material results in significant changes in reference values for some proteins. The establishment of new reference ranges will take a considerable time, and in the interim several professional societies and diagnostic companies have agreed to use consensus reference ranges based on studies already undertaken.

Effect of high hydrostatic pressure on the enzymic hydrolysis of beta-lactoglobulin B by trypsin, thermolysin and pepsin

Hydrolysis of beta-lactoglobulin B (beta-lg B) by pepsin, a process slow at ambient conditions, is facilitated at a moderately high hydrostatic pressure such as 300 MPa, corresponding to an apparent volume of activation delta V# = -63 ml mol-1 at pH 2.5, 30 degrees C and gamma/2 = 0.16. Digestion of beta-lg by trypsin and thermolysin is likewise enhanced by pressure, and the pressure effect has been traced to pressure denaturation of beta-lg B, which by high-pressure fluorescence spectroscopy has been shown to have a large negative volume of reaction, delta V(o) = -98 ml mol-1, at pH 6.7, 30 degrees C and gamma/2 = 0.16. Pressure denaturation is only slowly reversed following release of pressure and the enhanced digestibility is maintained at ambient pressure for several hours.

External quality assessment: currently used criteria for evaluating performance in European countries, and criteria for future harmonization

A questionnaire was circulated to European countries seeking information on the criteria used for acceptable performance in external quality assessment schemes. Responses were obtained from 21 countries. Fixed limits are used in 13 countries but the basis for these varies widely and includes clinical decision making, biological variation, views of experts, the state-of-the-art, and combinations of approaches. Variable limits based upon statistical analysis of the performance attained are used in 8 countries. The many advantages of harmonization in Europe have prompted the development of criteria based upon within- and between-subject biological variation for use in schemes which circulate single specimen challenges. Currently used criteria, which show much diversity, are compared with these proposals, and the empirical nature of the majority of the former is demonstrated.

Improved RNase protection assay for quantifying LDL-receptor mRNA; estimation of analytical imprecision and biological variance in peripheral blood mononuclear cells

We have improved the protocol for RNA quantification by using RNase protection. Instead of precipitation and extraction with phenol and chloroform, we use a faster and more reliable precipitation based on guanidinium thiocyanate (GdSCN). The internal standard is produced by in vitro transcription of a DNA template constructed so as to allow simultaneous detection of the in vitro transcript and the low-density lipoprotein receptor (LDLR) mRNA by use of the same probe and hybridization. Addition of this internal standard at the step for RNA isolation reduced the analytical imprecision from 40.8% to 19.3%. Estimates of the within- and between-subject biological variations of the LDLR mRNA content in peripheral blood mononuclear cells (PBMCs) isolated from healthy volunteers were 21.5% and 13.6%, respectively, and the analytical imprecision was 22.6%. The mean content of LDLR mRNA in PBMCs from healthy individuals was 0.78 copies per cell.

Improved RNase protection assay for quantifying LDL-receptor mRNA; estimation of analytical imprecision and biological variance in peripheral blood mononuclear cells

We have improved the protocol for RNA quantification by using RNase protection. Instead of precipitation and extraction with phenol and chloroform, we use a faster and more reliable precipitation based on guanidinium thiocyanate (GdSCN). The internal standard is produced by in vitro transcription of a DNA template constructed so as to allow simultaneous detection of the in vitro transcript and the low-density lipoprotein receptor (LDLR) mRNA by use of the same probe and hybridization. Addition of this internal standard at the step for RNA isolation reduced the analytical imprecision from 40.8% to 19.3%. Estimates of the within- and between-subject biological variations of the LDLR mRNA content in peripheral blood mononuclear cells (PBMCs) isolated from healthy volunteers were 21.5% and 13.6%, respectively, and the analytical imprecision was 22.6%. The mean content of LDLR mRNA in PBMCs from healthy individuals was 0.78 copies per cell.

Biological variation of serum and urinary magnesium in apparently healthy males

The biological variations of serum (S-) magnesium and urinary (U-) magnesium concentrations and excretions have been investigated. Serum samples, 24-h and fasting urinary samples were collected from each of 60 supposedly healthy male volunteers. In addition, 12 volunteers collected additional samples 7 and 112 days after the initial sample. The reference interval for S-magnesium was 0.765-0.997 mmol l-1. The biological variation for S-magnesium was 3.2% within subjects and 7.4% between subjects. This indicated an index of indivduality of 0.5, which means that significant changes in S-magnesium can occur within the limits of the reference interval, and that serial determinations of S-magnesium might prove useful as an indicator of changes in whole body magnesium status. It is, on the other hand, unlikely that a single determination of S-magnesium can be used in assessing whole-body magnesium status in the individual. The reference interval for the 24-h U-magnesium excretion, corrected for surface area, was 1.306-4.762 mumol min-1 1.73 m-2. The 24-h U-magnesium excretion exhibited a biological within-subject variation of 36% and a between-subject variation of 26%. The 24-h U-magnesium excretion did not correlate with S-magnesium, and only slightly (r = 0.58) with the fasting U-magnesium/creatinine concentration. This, and the very large coefficients of variation, make it unlikely that the renal magnesium excretion can be used as a measure of whole body magnesium status, or that changes in the renal magnesium excretion can be used as a measure of changes in whole body magnesium status.

Separate estimation of biological and analytical variance components when quantities and reagents are unstable

A model for reliable estimation of variance components for biological within- and between-subject variation as well as for analytical variation when both the quantity and the reagents are unstable has been established. This model was applied to the alpha-interferon receptor on human leucocytes which involves two major problems. First, the receptor has to be quantified within a few hours after blood sampling, and second, the reagents for the measurement procedure must be used within 2 weeks. For the number of receptors per cell the biological estimates of coefficients of variation were 14% for within-subject variation and 20% for between-subject variation, respectively. For the dissociation constant both estimates were zero as expected. The model is robust and applicable to other systems with unstable quantities and reagents.