ISO 17511:2003 In vitro diagnostic medical devices

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ISO 17511:2003 In vitro diagnostic medical devices

Description

ISO 17511:2003 In vitro diagnostic medical devices -- Measurement of quantities in biological samples -- Metrological traceability of values assigned to calibrators and control materials: For measurements of quantities in laboratory medicine, it is essential that the quantity is adequately defined and that the results reported to the physicians or other health care personel and patients are adequately accurate (true and precise) to allow correct medical interpretation and comparability over time and space.

Abbreviation: ISO 17511:2003


MitoPedia concepts: MitoFit Quality Control System 






Publicly available informative sections of standards

Introduction
In this European Standard the concept "accuracy of measurement" (see 3.1) is related to both "trueness of measurement" (see 3.33) and "precision of measurement" (see 3.23) whereas the Directive 98/79/EC on in vitro diagnostic medical devices uses the term "accuracy" instead of "trueness".
To allow 'correct medical interpretation' involves more than the metrological (analytical) aspects of the traceability chain. As the measurement results are eventually used by the physician for the benefit of the patients, the physician should gather information on a number of other aspects, such as knowledge about the pre- and post-analytical phase, the diagnostic sensitivity and specificity, and relevant reference interval(s). The present European Standard deals only with the analytical aspects of measurements in Laboratory Medicine (see also 1 e)).
The measurement of quantities in biological samples requires reference measurement systems including:
— the definition of the analyte in the biological sample with regard to the intended clinical use of the measurement results;
— a reference measurement procedure for the selected quantity in human samples;
— suitable reference materials for the selected quantity, e.g. primary calibrators and secondary matrix-based calibrators that are commutable.
The trueness of measurement of a value assigned to a defined quantity of a calibrator or trueness control material, depends on the metrological traceability of the value through an unbroken chain of alternating measurement procedures and measurement standards (calibrators), usually having successively decreasing uncertainties of measurement. The uncertainty of the value assigned to a given calibrator or trueness control material depends on the stated metrological traceability chain and the combined uncertainties of its links.
The ideal end-point of a metrological traceability chain is the definition of the relevant unit of the International System of Units (SI), but the selection of steps and the level at which metrological traceability for a given value stops, depend on the availability of higher order measurement procedures and calibrators. In many cases, at present, there is no metrological traceability above the manufacturer's selected measurement procedure or the manufacturer's working calibrator. In such cases, trueness is referred to that level of the calibration hierarchy until an internationally agreed reference measurement procedure and/or calibrator becomes available.
The objective of a chosen metrologically traceable calibration is to transfer the degree of trueness of a reference material, and/or reference measurement procedure, to a procedure that is of a lower metrological order, e.g. a routine procedure. Metrological traceability of calibration requires that the reference and routine measurement procedures measure the same measurable quantity with an analyte of the same pertinent characteristics.
In this context, it is important to recognize that different procedures purporting to measure the same quantity may in fact give different results when applied to a particular sample or reference material.
Depending on the possibility of metrological traceability to SI and on the availability of various metrological levels of measurement procedures and calibrators, the following five typical upper ends of the metrological traceability chain can be identified.
  1. Quantities for which results of measurements are metrologically traceable to SI. A primary reference measurement procedure and one or more (certified) primary reference materials (used as calibrators) are available.
  2. Quantities for which results of measurements are not metrologically traceable to SI.
    1. An international conventional reference measurement procedure (which cannot be called a primary reference measurement procedure) and one or more international conventional calibration materials with values assigned by that procedure are available.
    2. An international conventional reference measurement procedure is available but no international conventional calibration materials.
    3. One or more international conventional calibration materials (used as calibrators) with a protocol for value assignment are available, but no international conventional reference measurement procedure.
  3. Neither reference measurement procedure nor reference materials for calibration are available. The manufacturer can establish 'in-house' measurement procedure(s) and calibrator(s) to support value assignment to his product calibrator.
Scope
ISO 17511:2003 specifies how to assure the metrological traceability of values assigned to calibrators and control materials intended to establish or verify trueness of measurement. The calibrators and control materials are those provided by the manufacturers as part of, or to be used together with, in vitro diagnostic medical devices.
External quality assessment (survey) samples, with proven commutability, whose values have been assigned by means of internationally agreed reference measurement systems or internationally agreed conventional reference measurement systems fall within the scope of ISO 17511:2003.
This European Standard is not applicable to:
  1. control materials that do not have an assigned value and are used only for assessing the precision of a measurement procedure, either its repeatability or reproducibility (precision control materials);
  2. control materials intended for intralaboratory quality control purposes and supplied with intervals of suggested acceptable values, each interval obtained by interlaboratory consensus with respect to one specified measurement procedure, and with limiting values that are not metrologically traceable;
  3. correlation between results of two measurement procedures at the same metrological level, purporting to measure the same quantity, because such 'horizontal' correlation does not provide metrological traceability;
  4. calibration derived from correlation between the results of two measurement procedures at different metrological levels, but with quantities having analytes of different characteristics;
  5. metrological traceability of routine results to the product calibrator and their relations to any medical discrimination limit;
  6. properties involving nominal scales, i.e. where no magnitude is involved (e.g. identification of blood cells).
Terms and definitions
Accuracy of measurement: closeness of the agreement between the result of a measurement and a true value of the measurand [SOURCE: VIM:1993, 3.5]. Accuracy of measurement is related to both trueness of measurement and precision of measurement. Accuracy cannot be given a numerical value in terms of the measurand, only descriptions such as 'sufficient' or 'insufficient' for a stated purpose. An estimator of an inverse measure of accuracy is "deviation", defined as 'value minus a conventional true value'. ISO 3534-1, instead of "a true value" in the definition above, uses the concept "the accepted reference value", which can be a theoretical (true), assigned, consensus, or procedure-defined value. In this standard the concept "accuracy of measurement" is related to both "trueness of measurement" and "precision of measurement" whereas the Directive 98/79/EC on in vitro diagnostic medical devices uses the term 'accuracy' instead of 'trueness'.
Analyte: component represented in the name of a measurable quantity. EXAMPLE: In the type of quantity "mass of protein in 24-hour urine", "protein" is the analyte. In "amount of substance of glucose in plasma", "glucose" is the analyte. In both cases the long phrase represents the measurand.
Analytical specificity: ability of a measurement procedure to measure solely the measurand.
bias of measurements: difference between the expectation of the results of measurement and a true value of the measurand. An estimator is the "statistical sample bias of measurements" which is the 'average minus its reference value'.
Calibration: set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realized by standards [SOURCE: VIM:1993, 6.11]. The term "standard" here refers to "measurement standard", not a written standard.
Calibration transfer protocol: detailed description for assigning a value of a quantity to a reference material using a specified sequence of measurement procedures calibrated by higher-order reference materials for the same type of quantity.
Calibrator: calibration material reference material whose value is used for the independent variable in a calibration function.
Certified reference material (CRM): reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which establishes metrological traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence [SOURCE: slightly adapted from VIM:1993, 6.14].
Commutability of a material: closeness of agreement between the mathematical relationship of the measurement results obtained by two measurement procedures for a stated quantity in a given material, and the mathematical relationship obtained for the quantity in routine samples.
Influence quantity: quantity that is not the measurand but that affects the result of the measurement.
International conventional calibrator: international conventional calibration material; calibrator whose value of a quantity is not metrologically traceable to the SI but is assigned by international agreement. The quantity is defined with respect to the intended clinical application.
International conventional reference measurement procedure: measurement procedure yielding values that are not metrologically traceable to the SI but which by international agreement are used as reference values for a defined quantity NOTE The quantity is defined with respect to the intended clinical application.
International measurement standard: international standard; standard recognized by an international agreement to serve internationally as the basis for assigning values to other standards of the quantity concerned [SOURCE: VIM:1993, 6.2].
Matrix of a material system: totality of components of a material system except the analyte [SOURCE: EN 12287:1999, 3.3].
Matrix effect: influence of a property of the sample, other than the measurand, on the measurement of the measurand according to a specified measurement procedure and thereby on its measured value. A specified cause of a matrix effect is an influence quantity. The term 'matrix effect' is sometimes erroneously used for the lack of commutability due to a denatured analyte or an added non-genuine component ('surrogate analyte') meant to simulate the analyte.
Measurable quantity: attribute of a phenomenon, body or substance that may be distinguished qualitatively and determined quantitatively [SOURCE: VIM:1993, 1.1]. Properties that are expressed on a nominal scale are not measurable quantities. "Measurable quantity" is not to be confused with "analyte".
Measurand: particular quantity subject to measurement [SOURCE: VIM:1993, 2.6].
Measurement procedure: set of operations, described specifically, used in the performance of particular measurements according to a given method [SOURCE: VIM:1993, 2.5].
Measurement standard: material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit or one or more values of a quantity to serve as a reference [SOURCE: VIM:1993, 6.1]. A given measurement standard with an assigned value for one quantity can sometimes serve as a reference material for measurement procedures yielding values for more than one type of quantity. (For example, a reference material for cholesterol also serving for cholesterol esters that are measured after hydrolysis as cholesterol). The term 'standard' is used with two meanings: "measurement standard" and "written standard". The full terms should be used when doubt can arise.
Method of measurement: logical sequence of operations, described generically, used in the performance of measurements [SOURCE: VIM:1993, 2.4]. A method of measurement, due to its generalized description, does not have numerically specified performance characteristics. A given method can be the basis of one or more measurement procedures, each with inherent numerical values for its performance characteristics.
Metrological traceability: property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties [SOURCE: VIM:1993, 6.10]. Each comparison is effected by a (reference) measurement procedure defined in a calibration transfer protocol. There are several types of traceability. Therefore the term 'metrological traceability' is used in the present text.
Metrology: science of measurement. NOTE: Metrology includes all aspects both theoretical and practical with reference to measurements, whatever their uncertainty, and in whatever fields of science or technology they occur [SOURCE: VIM:1993, 2.2].
Precision of measurement: closeness of agreement between independent results of measurements obtained under stipulated conditions [SOURCE: ISO 3534-1:1993, 3.14]. Precision of measurement cannot be given a numerical value in terms of the measurand, only descriptions such as 'sufficient' or 'insufficient' for a stated purpose. The degree of precision is usually expressed numerically by the statistical measures of imprecision of measurements, such as standard deviation and coefficient of variation, that are inversely related to precision. "Precision" of a given measurement procedure is subdivided according to the specified precision conditions. "Repeatability" relates to essentially unchanged conditions and is often termed "withinserial" or "within-run precision". "Reproducibility" relates to changes in conditions, e.g. time, different laboratories, operators, and measuring systems (including different calibrations and reagent batches).
Primary reference material: reference material having the highest metrological qualities and whose value is determined by means of a primary reference measurement procedure. The concept "primary calibrator" is subordinate to "calibrator" (see 3.7) and to "primary reference material".
Primary reference measurement procedure: reference measurement procedure having the highest metrological qualities, whose operation can be completely described and understood, for which a complete uncertainty statement can be written down in terms of SI units, and where results are, therefore, accepted without reference to a measurement standard of the quantity being measured. The Consultative Committee on Amount of Substance (CCQM) uses the term "primary method of measurement", but the term "primary reference measurement procedure" in the present context is in conformity with VIM. The term "definitive method'" was omitted in VIM, but is sometimes used for a thoroughly investigated and evaluated reference measurement procedure of high accuracy.
Primary measurement standard: standard that is designated or widely acknowledged as having the highest metrological qualities and whose value is accepted without reference to other standards of the same quantity [SOURCE: VIM:1993, 6.4]. For reference materials, the value can be obtained by applying a primary reference measurement procedure.
Product calibrator: calibrator intended for use with the manufacturer's final product.
Reference material (RM): material or substance one or more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement procedure, or for assigning values to materials (adapted from VIM: 1993, 6.13). The adjective 'homogeneous' refers to the physical homogeneity between macroscopic parts of the material, not to any microheterogeneity between molecules of the analyte.
Reference measurement procedure: thoroughly investigated measurement procedure shown to yield values having an uncertainty of measurement commensurate with its intended use, especially in assessing the trueness of other measurement procedures for the same quantity and in characterizing reference materials [SOURCE: EN 12286:1998, 3.7].
Secondary measurement standard: standard whose value is assigned by comparison with a primary standard of the same quantity [SOURCE: VIM:1993, 6.5].
True value of a quantity: value consistent with the definition of a given particular quantity [SOURCE: VIM:1993, 1.19]. This is a value that would be obtained by a perfect measurement. True values are by nature indeterminate. The indefinite article "a", rather than the definite article "the", is used in conjunction with "true value" because there may be many values consistent with the definition of a given particular quantity. The 'definition of a given particular quantity' may have to include the measurement procedure applied. Therefore, a true value may depend on a specified measurement procedure.
Trueness control material: reference material that is used to assess the bias of measurement of a measuring system.
Trueness of measurement: closeness of agreement between the average value obtained from a large series of results of measurements and a true value. Definition adapted from ISO 3534-1:1993, 3.12 that has '...test results and an accepted reference value', which can be a theoretical (true), assigned, consensus, or procedure-defined value. Concerning the phrase 'a true value'. Trueness of measurement cannot be given a numerical value in terms of the measurand, only ordinal values (e.g. sufficient, insufficient). The degree of trueness is usually expressed numerically by the statistical measure bias that is inversely related to trueness and is the difference between the expectation of the results of measurement and a true value of the measurand.
Uncertainty of measurement: parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand [SOURCE: VIM:1993, 3.9]. The parameter can be, for example, a standard deviation (or a given multiple of it), or the half-width of an interval having a stated level of confidence. The components of uncertainty are evaluated experimentally from statistical distributions (Type A) or evaluated from assumed probability distributions based on experience or other information (Type B). All components are expressed as standard uncertainties that are combined into one final expression.
Validation: confirmation, through the provision of objective evidence that the requirements for a specific intended use or application have been fulfilled [SOURCE: EN ISO 9000:2000, 3.8.5].
Verification: confirmation, through the provision of objective evidence, that specified requirements have been fulfilled [SOURCE: EN ISO 9000:2000, 3.8.4].
Working measurement standard: standard that is used routinely to calibrate or check material measures, measuring instruments or reference materials [SOURCE: VIM:1993, 6.7].