PubMed Health⌕ Search

Biomedical subjects

R Dybkaer

Publications and source records attributed to R Dybkaer.

16 recordsLinked to original sources
PubMed1991

Reference materials--a main element in a coherent reference measurement system.

The analytical reliability of any measurement procedure requires a specifically designed, coherent reference measurement system, including interrelated measurement procedures and measurement standards such as reference materials. The latter may be characterized by three sets of characteristics. The general characteristics comprise origin, mode of production, physical state and phase, homogeneity, physical form, container, additives, storage conditions, stability, and dangerous properties. The specific characteristics describe molecular composition, analyte, purity, matrix, quantity of interest (including scale), assigned value, and uncertainty of measurement. The additional characteristics concern the way in which values for other characteristics were obtained, the hierarchical position of the material, certificate, instructions for use, and intended function. The problem areas of reference materials comprise definition of the appropriate analyte, purification, matrix, assignment of values, and nomenclature. The present ambiguous terminology is presented and a systematic structure of descriptive names is proposed (tab. 1).

Chemistry, Clinical↗
PubMed1991

Scales for measurement based on an antigen-antibody reaction.

In spite of sometimes complicated reaction sequences, the multitude of immunomethods all rely on the principle of a reaction between an antigen and an antibody and follows physico-chemical kinetics according to molecular relationships. The preferred kind-of-quantities for amount of analyte, therefore, should be number of entities (unit: 1) and amount-of-substance (mol)--both requiring definition of the elementary entity of the analyte--rather than mass (kg) and arbitrary amount-of-substance(procedure) (arbitrary unit). Derived kind-of-quantities for concentration (dividing by volume of system) and content (dividing by mass of system) are easily defined. The measurement scale is an ordered set of possible values that the quantity may take. Any scale should be described as to type and the magnitudes and number of possible values. The types comprise nominal (no magnitudes), ordinal (inequality of magnitudes), difference (equality of differences), and ratio scales (equality of ratios). Each scale is characterized by the statistics allowed with the measured values. The magnitudes of possible values are derived from the nature of the quantities being considered and the measurement procedure. The number of possible values will vary from two to many and depends on the uncertainty of results delivered by the procedure. With this systematic description, the ambiguous terms "qualitative" and "semiquantitative" may be abandoned. A given analyte in a certain type of system may give rise to values on any of the scales if it can be measured on a ratio scale because simpler and chemically less informative results may be obtained by transformation.

Antigen-Antibody Reactions↗
PubMed1991

A systematic nomenclature for quantities of the haemostatic system.

The complex interplay of coagulation factors, fibrinolytic factors, and inhibitors characterizing the haemostatic system causes difficulties for devising useful measures of its status in a patient as well as for their calibration, comparability, and nomenclature. The latter problem is addressed by constructing examples of systematic generic quantity names based on IUPAC and IFCC recommendations having the general format "System-Component; kind of quantity" and considering the possibilities for each of these three items with both single and multiple components. The kinds of quantity comprise mass concentration, (amount-of-) substance concentration, catalytic (activity) concentration, time, relative arbitrary (amount-of-) substance concentration, relative time, and reciprocal relative time. For the coagulation system, the relative time specified by the use of thromboplastin reference material WHO 67/40 and the characterization of other thromboplastins by comparison with that reference material is discussed. A descriptive systematic name for international sensitivity index (ISI) is orthogonal regression slope (ORS). The recalculated value for the relative time of coagulation of a sample using any thromboplastin and its ORS is currently called international normalized ratio (INR), but is simply a relative time with the ORS specified.

Blood Coagulation Factors↗
PubMed1990

General metrological requirements of clinical lipid measurements.

Quantities in blood, plasma, or serum having lipid components are often difficult to define, especially as regards the component which must be selected according to chemical, biological, and clinical considerations. The choice of generic quantities and their respective measurement procedures relates to clinical requirements of allowable uncertainty, effectiveness, comparability, and compatibility determining goals of analytical reliability. The measurement procedure should define preanalytical requirements and be based upon traceability from tertiary and secondary reference materials with reference procedure values to primary reference materials. Such materials and procedures should be established internationally. A comprehensive quality assurance system of internal quality control and external quality assessment is essential to ensure worldwide and continued comparability. Validation and transferability should also be demonstrated by regional or international collaboration. Transmutation of results between procedures requires extensive investigations.

Chemistry, Clinical↗
PubMed1989

Measurement, value, and scale.

The terms 'qualitative', 'semiquantitative', and 'quantitative' are used ambiguously. Based on international recommendations by IEC, IFCC, ISO, IUPAC, and OIML, and the work on scales by Stevens, a systematic terminology is presented. Measurement is considered to be the set of operations by which a value (consisting of a relational operator, and symbols, figures, or letters) is assigned to a quantity. The possible values constitute a scale that may be subdivided into classes. A hierarchy of four types of scale is characterized: nominal (values are independent of magnitude), ordinal (ranked according to magnitude), interval (equality of differences, arbitrary zero), and ratio scale (equality of ratios, absolute zero); each type allows a different set of statistical calculations. The type of scale is independent of its number of values or classes, or the uncertainty of measurement. The number of values on a scale is indicated by the terms two-value, three-value,..., multivalue and the number of classes analogously by two-class, etc. Examples of transformation of quantities are given.

Chemistry Techniques, Analytical↗
PubMed1986

Elements of good practice in decentralized clinical laboratories.

The possibilities of producing decentralized clinical laboratory data 'nearer the patient' has augmented rapidly during the last decennium due to both simple and sophisticated equipment, often intended to be operated by nonlaboratorians. The theory and practice of quality assurance in its wider sense has not kept pace with this development. The components of Good Laboratory Practice are presented under the headings: type of laboratory work, discipline, management, personnel, premises, safety, equipment, reagents, standard operating procedures, internal quality control, external quality assessment, method, dedicated operating procedure, syllabi, and clinical relevance. The projects currently being established by different national, regional, and international bodies to formulate guidelines should be coordinated to avoid duplication and conflict.

Chemistry, Clinical↗
PubMed1975

Problems of quantities and units in enzymology.

A knowledge of the molecular structure of an enzyme makes it possible to characterize it by different types of "amount": number (of elementary entities), mass, volume, and amount of substance. Another type of amount is obtained by measuring the rate of reaction of a suitable substrate change elicited by the enzyme in a special defined assay mixture; this way of using the catalytic effect has lead international bodies to different definitions of (kind of) quantity and unit. Their problems are discussed. A coherent scheme of the most important kinds of quantities employed by the enzymologist is presented. The dangers of converting results with one type of assay method to those of another are explained.

Enzymes↗