ISO 17511:2003 In vitro diagnostic medical devices

high-resolution terminology - matching measurements at high-resolution

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" is not in the list (MiP concept, Respiratory state, Respiratory control ratio, SUIT concept, SUIT protocol, SUIT A, SUIT B, SUIT C, SUIT state, Recommended, ...) of allowed values for the "MitoPedia concept" property. MitoFit Quality Control System"MitoFit Quality Control System" is not in the list (Enzyme, Medium, Inhibitor, Substrate and metabolite, Uncoupler, Sample preparation, Permeabilization agent, EAGLE, MitoGlobal Organizations, MitoGlobal Centres, ...) of allowed values for the "MitoPedia topic" property. 

From 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.

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