ISO 18153:2003

INTERNATIONAL ISO
STANDARD 18153
First edition
2003-08-15
In vitro diagnostic medical devices —
Measurement of quantities in biological
samples — Metrological traceability of
values for catalytic concentration of
enzymes assigned to calibrators and
control materials
Dispositifs médicaux de diagnostic in vitro — Mesurage des grandeurs
dans des échantillons d’origine biologique — Traçabilité métrologique
des valeurs de concentration catalytique des enzymes attribuées aux
agents d’étalonnage et aux matériaux de contrôle

Reference number
©
ISO 2003
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ii © ISO 2003 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 18153 was prepared by the European Committee for Standardization (CEN) in collaboration with
Technical Committee ISO/TC 212, Clinical laboratory testing and in vitro diagnostic test systems, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
Throughout the text of this document, read ".this European Standard." to mean ".this International
Standard.".
For the purposes of this International Standard, the CEN annex regarding fulfilment of European Council
Directives has been removed.
Contents
page
Foreword.v
Introduction .vi
1 Scope .1
2 Normative references .1
3 Terms and definitions.1
4 Metrological traceability chain and calibration hierarchy .3
4.1 Principles.3
4.2 Structure .4
5 Validation of metrologically traceable calibration.6
5.1 Principles.6
5.2 Analytical specificity of measurement procedures.6
5.3 Commutability of calibrators .7
5.4 Commutability of control materials.7
Annex A (informative) List of IFCC primary reference measurement procedures .8
Annex B (informative) List of certified reference materials (CRM).9
Bibliography .10
iv © ISO 2003 – All rights reserved

Foreword
This document (EN ISO 18153:2003) has been prepared by Technical Committee CEN/TC 140 "In vitro diagnostic
medical devices", the secretariat of which is held by DIN, in collaboration with Technical Committee ISO/TC 212
"Clinical laboratory testing and in vitro diagnostic test systems".
This European Standard EN ISO 18153:2003 including the Amendment shall be given the status of a national
standard, either by publication of an identical text or by endorsement, at the latest by February 2004, and
conflicting national standards shall be withdrawn at the latest by February 2004.
This document has been prepared under a mandate given to CEN by the European Commission and the European
Free Trade Association, and supports essential requirements of EU Directive(s).
For relationship with EU Directive(s), see informative annex ZA, which is an integral part of this document.
The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), the European Confederation of
Laboratory Medicine (ECLM), and the European Diagnostic Manufacturers Association (EDMA) have contributed to
its preparation.
This standard includes a Bibliography.
Annexes A and B are informative.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,
Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
Introduction
The Directive 98/79/EC on in vitro diagnostic medical devices requires that the metrologically traceability of values
assigned to calibrators and control materials be assured through available reference measurement materials and
reference measurement procedures of higher order. Following this concept, the European Standard
prEN ISO 17511 on "traceability" has been elaborated which describes a hierarchical order of measurement
procedures and calibration materials. The general rules expressed in that standard also apply to quantities
involving catalytic activity. Whenever possible, metrological traceability should be demonstrated to the SI unit which
forms the top of the calibration hierarchy.
For the measurement of the catalytic activity concentration of enzymes (hereafter called 'catalytic concentration'), a
hierarchy of calibrators and measurement procedures is described in the present standard. For enzyme
measurements, the definition of the derived coherent SI unit "mole per second cubic metre", given the special
name "katal per cubic metre" by the General Conference on Weights and Measures, is the top of the hierarchy
followed by a primary reference measurement procedure to which lower level measurement procedures,
calibrators, and control materials should be traced whenever possible.
Enzymes in blood or other biological fluids can be measured for diagnostic purposes in terms of their catalytic
concentrations. The analytical principle of the measurement of the catalytic rate of conversion of substrate has
considerable advantages of speed, low limit of detection, analytical specificity, and low cost. Results of catalytic
concentration measurements are only comparable if the enzyme activities are measured under the same
conditions. Therefore, an enzyme measurand cannot be described only by kind-of-quantity (e.g. catalytic
concentration), name of enzyme and of system, but requires also the specified measurement procedure and
especially the indicator component of the measured reaction. At the top of the calibration hierarchy, the
measurement procedure should be internationally agreed, e.g. 'creatine kinase measured by the conversion rate of
NADH in the IFCC reference measurement procedure'.
Thus, the primary reference measurement procedure is an integral part of the definition of the measurand and has
to be followed in all detail, e.g. as concerns:
� kind of substrate (where the specificity of the enzyme allows this to be varied) and its concentration,
� activators and their concentrations,
� direction of catalysed reaction,
� indicator component,
� buffer system and pH,
� temperature,
� pre-incubation time,
� material used for starting the reaction,
� lag time,
� reaction time.
vi © ISO 2003 – All rights reserved

The disadvantage of the procedure-dependence of the definition of the enzyme measurand and therefore of the
results of the measurements are well known: problems are caused in external quality assessment (EQA) and in

assessing the transferability of methods; a multiplicity of biological reference intervals exists with the consequent
risk of clinical misinterpretation of enzyme results. The standardization of routine enzyme measurements is
important to laboratory medicine, to improve the clinical utility and comparability of results through the elimination of
existing differences in biological reference intervals.
Two approaches can be considered:
a) the exclusive routine use of a recommended or standardized procedure for each enzyme;
b) calibration of one or more routine procedures by commutable enzyme calibration materials with values
assigned by a chosen reference measurement procedure.
The "recommended procedure" approach (a)) has been pursued vigorously for more than twenty years. It has had
considerable success in improving the quality and comparability of enzyme measurements and in discouraging the
use of analytically unsatisfactory procedures. However, the recommended-procedure-approach to standardization
appears to have reached the limits of its usefulness. Its disadvantages include: absence of a consensus of choice
among a number of differing recommendations; intentional or unintentional modification of recommended
procedures in routine use; unresponsiveness of recommended procedures to analytical and technical
improvement; and partly non-adaptability of recommended procedures to preferred automation. As a change in
routine enzyme procedures, whether recommended or not, inevitably entails a change of biological reference
values, it is understandably unwelcome to clinicians.
Improvement of the design and analytical performance of enzyme measurements will, and should, continue.
However, this should follow the normal practice of development and dissemination of scientific advances. Attempts
to develop and promote further standardized procedures for universal use are neither practicable nor desirable.
The "reference measurement procedure and calibration material" approach (b)) has, in contrast, received relatively
little attention. Among the objections that have been raised are:
1. lack of stable enzyme reference materials in appropriate matrices to serve as calibrators;
2. dissimilarity between candidate enzyme calibrators and the analyte enzymes in human samples, including
differences in isoforms;
3. absence of a constant inter-procedure ratio between a calibrating (reference) procedure and calibrated
(routine) procedure(s), for both the enzyme calibrator and patients' samples containing the analyte enzyme
(also described as a lack of commutability).
The converse of these objections constitutes a list of specifications, both for higher order enzyme reference
materials and for families of measurement procedures between which calibration is proposed. The calibrator should
be stable and have an analyte enzyme that is close in its catalytic properties within its matrix to those of the analyte
enzyme in the routine samples. The procedures themselves should have the same specificity for the catalytic
activity of the target enzyme.
Harmonization of the results of routine enzyme measurements can thus be achieved by selecting a reference
measurement procedure and identifying a family of related procedures for each clinically important enzyme.
Results obtained by any procedure included within such a family will be metrologically traceable to the chosen
reference measurement procedure.
...