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PubMed1982

[Determination of the catalytic activity of lipase by the continuous titration method].

Development of a standardized procedure for the titrimetric assay of lipase has been suggested. Comparative studies with triolein und olive oil were therefore undertaken. Optimal conditions, such as pH, substrate and glycocholate concentrations, etc. were determined for the assay with triolein. The results agree with those obtained earlier with olive oil as substrate. Experience with the quality of various reagents used since 1966 is reported. Problems of methodology are then discussed, especially the incomplete characterization and purity of the bile acid preparations, and their effects on the test conditions. A critical analysis shows that two point tests with modifications of the continuous titration cannot give reliable results. Haemolysis and its effect on catalytic activity of lipase are used to illustrate the consequences of the uncritical acceptance of data from the literature. Furthermore, the required sensitivity of the analytical equipment, operational errors, and the uncritical evaluation and interpretation of analytical data are discussed. The first experiments to be performed with the addition of colipase are described, and the question of whether this cofactor should be used routinely for test purposes is considered. The problem of whether lipoproteinlipase can be quantitatively inhibited is discussed. In view of the outlay on apparatus and the time required for the assay, continuous titration is definitely not suitable for routine screening purposes. On the other hand, simpler methods that give reproducible quantitative results have not yet been developed.

Catalysis↗

PubMed1985

Maximizing the efficiency of a study on alcohol-related birth defects by means of data collection and analytic strategy dissociation.

Application of the terms "prospective" and "retrospective" to quasi/experimental research designs used in clinical investigations is often ambiguous; they often lack specification as to whether they apply to data acquisition, analytic strategy, or both. Data may be collected prospectively by preplanned protocol or retrospectively by chart review. In addition, the direction of analysis may be prospective--comparing differential outcomes for at-risk and not at-risk (exposed/not exposed) groups--or retrospective--comparing differential preceding risks for affected and nonaffected groups. Prospective data collection is advantageous in assuring the availability of crucial variables for an entire sample, but prospective analytic strategies may be inefficient, underestimating effect sizes, particularly when the outcome of interest is rare or the effect, even if large, is seen in only a small proportion of cases. In a prospective multilinear regression model of risks for lowered birthweight for gestational age, 2% of the variance was explained by alcohol variables after adjustment for confounding. In comparison, a similar multilinear regression of case-control sample, in which the frequency of the abnormal outcome is raised, showed 18% of the variance explained by alcohol variables. Data collection and analytic strategies may be dissociated. Although some statistical power may be lost because of reduced sample size, synthetic case-control analysis is efficient in examining small effects. It also has the advantage of decreasing the size of the database to be managed and the time required for analysis. Using this approach, it is feasible to perform virtually any analysis that can be done on a mainframe on medium-sized departmental computer system.

Birth Weight↗

PubMed1993

Chemistry with confidence: should Clinical Chemistry require confidence intervals for analytical and other data?

Confidence intervals are not commonly provided with analytical or other data reported in Clinical Chemistry although P values are. However, confidence intervals provide an explicit demonstration of the direction and magnitude of uncertainty and are intuitively easy to grasp, unlike P values. It is therefore argued that the Journal should adopt a policy requiring the provision of confidence intervals. Such a policy would improve the statistical rigor of Journal reports.

Chemistry, Clinical↗

PubMed1985

Fluoride content of selected human food, pet food and related materials.

A survey was made of the fluoride content of selected human foods, some animal feeds, and related materials, with the purpose of a better characterization of products whose fluoride may contribute to the intake of fluoride by man as well as by some kinds of animals. Uptake of fluoride, especially from food with or without a foregoing food chain, was found to be more widely spread than has been documented previously. The major source of fluoride is represented by marine organisms, regardless of the ways by which man or animals are exposed to fluoride. As a consequence of the detailed analytical data given, recommendations would extend towards i) a more wide-spread analytical control of foods and feeds for fluoride, ii) an intensified assessment of fluoride bioavailabilities from foods and feeds, and iii) the consideration of such data in the evaluation of fluoride supplementations for optimized intakes, as recommended.

Animal Feed↗

PubMed1979

Classification of fungi by means of pyrolysis-gas chromatography-pattern recognition.

Repetitive samples of three strains of the mould Penicillium were subjected to pyrolysis-gas chromatography (Py-GC). From the chromatograms, 26 peak heights were used in a subsequent SIMCA pattern recognition analysis. This data analysis gives a marked improvement in the classification of the samples (100% correct, 85% unique) in comparison with the traditional analysis based on the average chromatogram of each class (92% correct, 45% unique). The data analytical method is described in detail using the Py-GC data as an illustration.

Analysis of Variance↗

PubMed1983

Use of anion gap for the quality control of electrolyte analyzers.

A simple model for the simulation of patient Na, CO2, Cl, and anion gap was formulated from patient electrolyte data. Analytical error, either random or systematic, was incorporated into the simulation of the electrolyte data and allowed study of the response of anion gap to error. Power functions, plots of probability of error detection vs. size of analytical error, were constructed and indicated a low probability of error detection when single patient specimens with abnormal anion gaps were reanalyzed. These power functions showed that pooling of the anion gap data by averaging consecutive anion gaps resulted in a high probability for detecting systematic error. We recommend, as a useful quality control procedure, averaging at least eight consecutive anion gaps and testing for a significant difference between the average and the established mean gap.

Acid-Base Equilibrium↗

PubMed1995

Standard reference materials and data quality assurance: the lesson from the analysis of trace elements.

The problem of having accurate and precise analytical data of the concentrations of trace elements and compounds in bioclinical studies is of fundamental importance. This can be conveniently faced if appropriate standard reference materials, with known concentrations of the analyte object of study, are available. This paper reviews the present situation of these standard materials in the field of trace element analysis in biological specimens. The most important requirements in the preparation and in the application of these materials are presented and discussed.

Evaluation Studies as Topic↗

PubMed1990

Epidemiology of adenocarcinoma of the cervix.

There is general evidence that the incidence of adenocarcinoma of the cervix has been rising, particularly among younger women. The determinants of these trends, however, remain largely unknown. We have reviewed the epidemiology of adenocarcinoma of the cervix using descriptive data from cancer registration and clinical series and two main sources of analytical data: clinical studies comparing cervical adenocarcinoma (AC) and squamous carcinoma (SC) and formal case-control and cohort epidemiological studies. In both the United States and northern Europe there is evidence of the rising frequency of AC in absolute and relative terms as compared to SC. These trends are generally restricted to younger women: under-age-35 AC incidence approximately doubled from the early 1970s to the early 1980s. Available data, although scanty, consistently show that the frequency of cervical adenocarcinoma rises with the number of partners and with decreasing age at first intercourse, suggesting a potential role for sexually transmitted (viral) factors. In clinical series, nulliparity was reported more frequently in AC than in SC cases but an inconsistent association was found in three formal epidemiological studies. Similarities with the epidemiology of endometrial cancer are also suggested from the association with overweight, while a possible relation with hypertension and diabetes is based on clinical series only and hence more difficult to interpret. Thus, adenocarcinoma of the cervix appears to share epidemiological characteristics with both adenosquamous cancer of the cervix and adenocarcinoma of the endometrium, although uncertainties in classification and registration leave several questions unanswered.

Adenocarcinoma↗

PubMed1993

[The benefits of auditing clinical histories. Our experience over 5 years].

OBJECTIVE: To evaluate how our clinical records (CR) are filled in and to observe the impact of measures taken to correct faults found over a five-year follow-up period. DESIGN: Three descriptive studies (auditing methodologies) on representative samples of CR selected at random. Four quality indicators were fixed: internal communication (i.e. legibility and comprehensibility), external communication, manageability and the quality of the activity at attendances measured by the SOAP. The optimum standards (OS) were agreed by the team (technique of nominal group). SETTING: "Florida" Health Centre, Alicante. PATIENTS AND OTHERS PARTICIPANTS: Periodic team meetings to analyse results and agree activities. In 1986, N of CR = 367; in 1988, 370; and in 1990, 372. MAIN MEASUREMENTS AND RESULTS: During the follow-up period, the filling-in of all the variables, except the address, the test carried out and blood pressure, improved. But the following did not reach the OS: code, affiliation, origin, instruction, habits, allergies, working activity, socio-economic data, age and gender, family/personal background, test carried out, blood pressure and analytical data. The following all reached the OS: legibility, which went up from 88% to 96.5%, comprehensibility from 62 to 75.3%, external communication from 81 to 88.9%, manageability from 53 to 79.6% and SOAP from 62 to 82.5%. CONCLUSIONS: Auditing allows the level of the filling-in of the CR to be measured. Deficiencies which appear to be due to the design of the record itself can be detected. The efficacy of corrective measures to improve records can also be assessed.

Communication↗

PubMed1986

Modifications of lipid structure and their influence on mesomorphism in model membranes: the influence of hydrocarbon chains.

The influence of hydrocarbon chains on the temperature (TG-LC) of the gel to liquid-crystalline phase transition of model membranes has been investigated over an extensive variety of phosphatidylcholines (PC). The TG-LC is dependent upon the length of the hydrocarbon chains, on whether or not the chains are saturated or have been modified in some way, and on the position of any modification along the chain. For PC having two different acyl chains (heteroacid PC) in the sn-1 and sn-2 positions, the TG-LC is dependent on the chain position and on the inequivalence of chain penetration into the bilayer. Positional isomers of PC have different TG-LC. The first two double bonds introduced in each chain of a PC cause a much greater reduction in TG-LC and in the enthalpy change of the transition than does the subsequent introduction of additional double bonds. Dipolyunsaturated PC have uncooperative (broad) transitions that occur at low temperatures and have small enthalpy changes. While each PC has unique transitional characteristics, there are a number of patterns in the TG-LC which emerge on consideration of all the available data. One such pattern may be useful in predicting TG-LC from analytical data on the composition and positions of acyl chains of various lipids.

Chemical Phenomena↗

PubMed1990

Evaluation of criteria for the acceptance of bioanalytical data.

Results from bioanalytical analyses for registration of a new drug entity are used to define its pharmacokinetics and bioavailability/bioequivalence. Whilst analytical data may be derived from the application of a validated method, it is essential to apply mathematical criteria to its acceptance, in order that the analyst can be assured that the assay is performing within defined limits and to its validated specification. Parameters evaluated for acceptability are the batch calibration curve, the minimum quantifiable concentration and the quality control (QC) sample acceptability. Specifically, six QC samples per analytical batch are used, two samples at each of three concentrations. The rationale for the definition of these criteria is evaluated together with a consideration of their applications and limitations. The relevance and use of Shewhart and Cusum plots to monitor assay performance is illustrated.

Biological Availability↗

PubMed1991

Advances in data assessment. Application to the etiology of nausea reported during chemotherapy, concerns about significance testing, and opportunities in clinical trials.

Typical inferential statistical procedures, such as the t-test and analysis of variance, compare differences in mean values of variables. This approach can sometimes obscure rather than illuminate research data. Here we present and discuss alternative data analytic techniques. Potential advantages of box plots over conventional t-tests for understanding data are shown by comparing the area under high and low frequencies from spectral curves of autonomic changes following chemotherapy treatment. Typical t-tests provide information regarding statistical significance in terms of the differences in group means; box plots and related exploratory techniques provide information regarding the characteristics of the distributions within the groups as well as examination of potential outliers. Multivariate analysis of variance (MANOVA) and other multivariate techniques are commonly used to deal with potentially complex data sets with multiple outcome measures. The potential advantages of visual clustering techniques such as star plots, Chernoff faces, and Andrew's Function Plots are demonstrated by examining changes in facial pallor caused by chemotherapy-induced nausea and vomiting. Typical MANOVA approaches can identify potential differences in mean values between groups; visual clustering approaches do this by graphically presenting complex interrelationships for individual cases. This approach enhances the visual interpretation of potential interactions that would be obscured by simply focusing on overall mean values. Preliminary data from a meta-analysis on the effect of metoclopramide on chemotherapy-induced vomiting demonstrates the potential uses and advantages of this summary technique over simple tabular summaries. We found significant relationships between the effect size of the drug and variables such as the year of study publication and whether the publication was an article or an abstract. While none of these techniques are meant to replace traditional inferential statistics, they offer advantages in terms of data exploration and understanding relationships within data sets that are not clearly addressed by other methods. They are potentially valuable alternatives worthy of exploration. Finally, we discuss issues of interim analyses and multiple endpoint assessment for clinical trials.

Antineoplastic Agents↗

PubMed1997

Limitations of the coupling of amino acid mixtures for the preparation of equimolar peptide libraries.

The standard method of peptide library synthesis involves coupling steps in which a single amino acid is reacted with a mixture of resin-bound amino acids. The more recently described positional scanning strategy (in which each position in the peptide sequence is occupied in turn by a single residue) is different since it involves the coupling of mixtures of amino acids to mixtures of resin-bound amino acids. In the present study, we analyze the compounds produced under these conditions measuring coupling rates and amounts of formed products, using mainly UV, HPLC, LC/MS and MS/MS techniques. Our data do not permit to conclude that the resulting libraries are complete. Indeed, our analytical data indicate that a large part of the di-, tri- and tetrapeptides synthesized with this method are not present in the final mixture. Although chemical compensation (in which poor coupling kinetics is compensated by a larger excess of the incoming amino acid) has been thought to counterbalance these biases, our experiments show that the compensation method does not take into account the crucial influence of the resin-bound amino acid and that even the dipeptide libraries obtained in this way are far from completeness. The present work provides strong evidence that the coupling of mixtures of amino acids to resin-bound residues, which is required by the positional scanning strategy, results in incomplete and/or non-equimolar libraries. It also clearly confirms that coupling rates in solid-phase peptide synthesis are dependent on the nature of both the incoming and the immobilized amino acid.

Amino Acids↗

PubMed1986

Novel sulfur-containing microbial metabolite of primaquine.

Microbial metabolism studies of the antimalarial drug primaquine, using Streptomyces roseochromogenus (ATCC 13400) have produced an N-acetylated metabolite and a methylene-linked dimeric product, both of which have been previously reported, and a novel sulfur-containing microbial metabolite. The structure of the metabolite as a sulfur-linked dimer was proposed on the basis of spectral and chemical data. The molecular formula C34H44N6O4S was established from field-desorption mass spectroscopy and analytical data. The 1H- and 13C-nuclear magnetic resonance spectral data firmly established that the novel metabolite was a symmetrically substituted dimer of primaquine N-acetate with a sulfur atom linking the two units at C-5. The metabolite has been shown to be a mixture of stereoisomers which can equilibrate in solution. This observation was confirmed by microbial synthesis of the metabolite from optically active primaquine.

Chemical Phenomena↗

PubMed1994

Employing simulated data to illustrate an important cause of the 'steepling' effect in breath alcohol analysis.

The 'steepling' effect (large excursions in analytical data over time) is a debated issue in forensic breath alcohol analysis with various explanations being postulated. Simulated breath alcohol data was generated according to a hypothetical kinetic model where single random samples as well as means of duplicate random samples were plotted with respect to time at 0.2 hour intervals. In addition, the simulated data was compared when both two or more digit treatment was employed. Results showed the occurrence of significant noise or 'steepling' when single, two-digit breath alcohol samples were employed as compared to a four-digit mean computed from three-digit duplicates. The magnitude of variability was quantified by means of nonlinear regression resulting in the residual sum of squares (RSS) = 0.00202 for the single analysis and RSS = 0.00053 for the mean of duplicates. The method of data collection and treatment appears to contribute significantly to the 'steepling' phenomenon. Intuitively, replicate analyses reduce variability and allow for more accurate kinetic modelling employing breath alcohol analysis.

Alcoholic Intoxication↗

PubMed1988

Elemental microanalysis of biological specimens.

Although X-ray microanalysis in the electron microscope is the most common method for microanalysis of biological specimens, other methods of elemental microanalysis (electron energy loss spectroscopy, scanning Auger microanalysis, and proton, ion, and laser microprobe analysis) may provide important complementary information and help overcome some of the limitations of electron probe X-ray microanalysis. Despite differences in physical principles and instrumentation, the various microanalytical methods have much in common with regard to specimen preparation, quantitative analysis, and interpretation of analytical data. A common approach to microanalytical problems in the biological sciences, irrespective of the analytical techniques used, seems therefore indicated.

Electron Probe Microanalysis↗

PubMed1993

Pesticide residue control in the years 1988-1989 in Italy.

The paper reports the monitoring for pesticide residue contamination of foodstuffs carried out in the years 1988-1989 by the Italian peripheral laboratories officially commissioned for the task. The tables show the analytical data for each class of substrate versus the limits in force at the time. 2506 food samples and 555 samples from the environment were analysed and a total of 16,259 determinations made. The residues were absent in 90% of the cases; the percentage of irregularities was 1.52%. These results confirm the data obtained in previous years, which is particularly significant considering the much larger number of analytical determinations performed this time. It has been deemed convenient to survey specific types of foodstuffs (for example, cereals and animal products) by examining a larger number of samples.

Edible Grain↗

PubMed1992

Clinical pathology: preanalytical variation in preclinical safety assessment studies--effect on predictive value of analyte tests.

Significant differences in concentrations of analytes in samples may be introduced before samples enter analyzers. These differences are known as preanalytical variation and are part of the overall variation in analytical data. Preanalytical variation is caused by factors that operate during animal preparation prior to sampling, sample collection, sample processing, and sample storage prior to measurement. Preanalytical variation is important because it detracts from the predictive value of analyte measurements. Preanalytical variation may permanently damage data. Because its effects are difficult to quantitate it should be minimized in safety assessment studies. Sources of preanalytical variation are actions performed on animals prior to sample collection and actions performed on the specimen prior to analysis. Preanalytical variation produces a range of artefacts in experimental data. Consequences of preanalytical variation are loss of confidence in the data, obfuscation of real test article effects, false effects, and possibly the expense of repeating a study. To limit preanalytical variation, its sources must be identified, the effects documented, and measures devised to eliminate its sources. Predictive value (likelihood of actual disease) of appropriate clinical pathology tests in toxicology is inversely dependent on preanalytical variation: uncontrolled variation produces data with low predictive values, and controlled variation produces data with high predictive values.

Animals↗