SIST EN ISO 20776-2:2022
(Main)Clinical laboratory testing and in vitro diagnostic test systems - Susceptibility testing of infectious agents and evaluation of performance of antimicrobial susceptibility test devices - Part 2: Evaluation of performance of antimicrobial susceptibility test devices against reference broth micro-dilution (ISO 20776-2:2021)
Clinical laboratory testing and in vitro diagnostic test systems - Susceptibility testing of infectious agents and evaluation of performance of antimicrobial susceptibility test devices - Part 2: Evaluation of performance of antimicrobial susceptibility test devices against reference broth micro-dilution (ISO 20776-2:2021)
This document establishes acceptable performance criteria for antimicrobial susceptibility test
(AST) devices that are used to determine minimum inhibitory concentrations (MIC) of bacteria to
antimicrobial agents in medical laboratories.
This document specifies requirements for AST devices and procedures for assessing performance of
such devices. It defines how a performance evaluation of an AST device is to be conducted.
This document has been developed to guide manufacturers in the conduct of performance evaluation
studies.
Labormedizinische Untersuchungen und In-vitro-Diagnostika-Systeme - Empfindlichkeitsprüfung von Infektionserregern und Evaluation von Geräten zur antimikrobiellen Empfindlichkeitsprüfung - Teil 2: Evaluation der Leistung einer Vorrichtung zur antimikrobiellen Empfindlichkeitsprüfung (ISO 20776-2:2021)
Dieses Dokument legt annehmbare Leistungskriterien für Testsysteme zur Prüfung der mikrobiellen Empfindlichkeit (AST, en: antimicrobial susceptibility test) fest, die zur Bestimmung der minimalen Hemmkonzentrationen (MHK) von Bakterien auf antimikrobielle Substanzen in medizinischen Laboren verwendet werden.
Dieses Dokument legt Anforderungen an Testsysteme zur Prüfung der mikrobiellen Empfindlichkeit sowie Verfahren zur Leistungsbewertung dieser Testsysteme fest. Es legt fest, wie eine Leistungsbewertung eines Testsystems zur Prüfung der mikrobiellen Empfindlichkeit durchzuführen ist.
Dieses Dokument wurde mit dem Ziel erarbeitet, Hersteller bei der Durchführung von Leistungsbewertungs-studien anzuleiten.
Systèmes d'essais en laboratoire et de diagnostic in vitro - Sensibilité in vitro des agents infectieux et évaluation des performances des dispositifs pour antibiogrammes - Partie 2: Évaluation des performances des dispositifs pour antibiogrammes par rapport à une méthode de référence de microdilution en bouillon (ISO 20776-2:2021)
Le présent document établit des critères de performances acceptables pour les dispositifs de mesure de sensibilité antimicrobienne (DMSA), qui sont utilisés pour déterminer les concentrations minimales inhibitrices (CMI) de bactéries des agents antimicrobiens dans des laboratoires médicaux.
Le présent document indique les exigences pour les dispositifs DMSA, ainsi que les modes opératoires permettant d’estimer la performance de ces dispositifs. Il définit comment une évaluation des performances d’un dispositif DMSA doit être effectuée.
Le présent document a été développé afin de guider les fabricants dans la réalisation des études d’évaluation des performances.
Klinični laboratorijski preskusi ter diagnostični preskusni sistemi in-vitro - Preskus občutljivosti povzročiteljev infekcij in vrednotenje delovanja antimikrobno občutljivih preskusnih naprav - 2. del: Vrednotenje delovanja antimikrobno občutljivih naprav (ISO 20776-2:2021)
Ta dokument določa kriterije sprejemljivega delovanja antimikrobno občutljivih naprav (AST), ki se uporabljajo za določevanje minimalnih inhibicijskih koncentracij (MIC) antimikrobnih sredstev za bakterije v zdravstvenih laboratorijih.
Ta dokument določa zahteve za antimikrobno občutljive naprave in postopke za ocenjevanje njihovega
delovanja. Opredeljuje način vrednotenja delovanja antimikrobno občutljive naprave.
Ta dokument je bil pripravljen za usmerjanje proizvajalcev pri izvajanju študij vrednotenja
delovanja.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 20776-2:2022
01-marec-2022
Nadomešča:
SIST EN ISO 20776-2:2008
Klinični laboratorijski preskusi ter diagnostični preskusni sistemi in-vitro -
Preskus občutljivosti povzročiteljev infekcij in vrednotenje delovanja antimikrobno
občutljivih preskusnih naprav - 2. del: Vrednotenje delovanja antimikrobno
občutljivih naprav (ISO 20776-2:2021)
Clinical laboratory testing and in vitro diagnostic test systems - Susceptibility testing of
infectious agents and evaluation of performance of antimicrobial susceptibility test
devices - Part 2: Evaluation of performance of antimicrobial susceptibility test devices
against reference broth micro-dilution (ISO 20776-2:2021)
Labormedizinische Untersuchungen und In-vitro-Diagnostika-Systeme -
Empfindlichkeitsprüfung von Infektionserregern und Evaluation von Geräten zur
antimikrobiellen Empfindlichkeitsprüfung - Teil 2: Evaluation der Leistung einer
Vorrichtung zur antimikrobiellen Empfindlichkeitsprüfung (ISO 20776-2:2021)
Systèmes d'essais en laboratoire et de diagnostic in vitro - Sensibilité in vitro des agents
infectieux et évaluation des performances des dispositifs pour antibiogrammes - Partie 2:
Évaluation des performances des dispositifs pour antibiogrammes par rapport à une
méthode de référence de microdilution en bouillon (ISO 20776-2:2021)
Ta slovenski standard je istoveten z: EN ISO 20776-2:2022
ICS:
11.100.10 Diagnostični preskusni In vitro diagnostic test
sistemi in vitro systems
SIST EN ISO 20776-2:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 20776-2:2022
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SIST EN ISO 20776-2:2022
EN ISO 20776-2
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2022
EUROPÄISCHE NORM
ICS 11.100.20 Supersedes EN ISO 20776-2:2007
English Version
Clinical laboratory testing and in vitro diagnostic test
systems - Susceptibility testing of infectious agents and
evaluation of performance of antimicrobial susceptibility
test devices - Part 2: Evaluation of performance of
antimicrobial susceptibility test devices against reference
broth micro-dilution (ISO 20776-2:2021)
Systèmes d'essais en laboratoire et de diagnostic in Labormedizinische Untersuchungen und In-vitro-
vitro - Sensibilité in vitro des agents infectieux et Diagnostika-Systeme - Empfindlichkeitsprüfung von
évaluation des performances des dispositifs pour Infektionserregern und Evaluation von Geräten zur
antibiogrammes - Partie 2: Évaluation des antimikrobiellen Empfindlichkeitsprüfung - Teil 2:
performances des dispositifs pour antibiogrammes par Evaluation der Leistung einer Vorrichtung zur
rapport à une méthode de référence de microdilution antimikrobiellen Empfindlichkeitsprüfung (ISO 20776-
en bouillon (ISO 20776-2:2021) 2:2021)
This European Standard was approved by CEN on 16 December 2021.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20776-2:2022 E
worldwide for CEN national Members.
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SIST EN ISO 20776-2:2022
EN ISO 20776-2:2022 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 20776-2:2022
EN ISO 20776-2:2022 (E)
European foreword
This document (EN ISO 20776-2:2022) has been prepared by Technical Committee ISO/TC 212 "Clinical
laboratory testing and in vitro diagnostic test systems" in collaboration with Technical Committee
CEN/TC 140 “In vitro diagnostic medical devices” the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by July 2022, and conflicting national standards shall be
withdrawn at the latest by January 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 20776-2:2007.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard : Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 20776-2:2021 has been approved by CEN as EN ISO 20776-2:2022 without any
modification.
3
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SIST EN ISO 20776-2:2022
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SIST EN ISO 20776-2:2022
INTERNATIONAL ISO
STANDARD 20776-2
Second edition
2021-12
Clinical laboratory testing and in
vitro diagnostic test systems —
Susceptibility testing of infectious
agents and evaluation of performance
of antimicrobial susceptibility test
devices —
Part 2:
Evaluation of performance of
antimicrobial susceptibility test
devices against reference broth micro-
dilution
Systèmes d'essais en laboratoire et de diagnostic in vitro — Sensibilité
in vitro des agents infectieux et évaluation des performances des
dispositifs pour antibiogrammes —
Partie 2: Évaluation des performances des dispositifs pour
antibiogrammes par rapport à une méthode de référence de
microdilution en bouillon
Reference number
ISO 20776-2:2021(E)
© ISO 2021
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SIST EN ISO 20776-2:2022
ISO 20776-2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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SIST EN ISO 20776-2:2022
ISO 20776-2:2021(E)
Contents Page
Foreword .iv
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test methods . 5
4.1 General . 5
4.2 Methods . 5
4.2.1 Reference method . . 5
4.2.2 Strain selection . 5
4.2.3 Quality control (QC) . 6
4.2.4 Quality control (QC) of the reference method . 6
4.2.5 Reproducibility testing of test device . 6
4.2.6 Isolate testing protocol . 7
4.2.7 Inoculum preparation . 7
4.2.8 Discrepancy resolution testing . 7
4.2.9 System under evaluation . 7
5 Data analysis and acceptance criteria . 8
5.1 Accuracy of test device . 8
5.1.1 General . 8
5.1.2 MIC devices . 8
5.1.3 Qualitative AST devices . 8
5.2 Quality control (QC) of test device . 8
5.3 Reproducibility of test device . 8
5.4 Documents related to study . 8
Annex A (informative) Evaluating the performance of MIC tests . 9
Annex B (informative) Rationale for bias analysis .12
Annex C (informative) Sensitivity and specificity analyses for qualitative tests .14
Bibliography .16
iii
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SIST EN ISO 20776-2:2022
ISO 20776-2:2021(E)
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 non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 212, Clinical laboratory testing and in
vitro diagnostic test systems, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 140, In vitro diagnostic medical devices, in accordance with the Agreement
on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 20776-2:2007), which has been
technically revised.
The main changes are as follows:
— Revision in the title of this document to better align with the intended information.
— Addition of an Introduction (not present in the first edition).
— Revised Clause 3 as follows:
— Removed definitions for category agreement, susceptible, intermediate, resistant, non-
susceptible, major discrepancy, minor discrepancy, very major discrepancy, breakpoint test
and zone diameter;
— Added definition for contemporary isolate (3.11.1), and removed definitions for fresh isolate,
recent isolate;
— Added definitions for reproducibility (3.9), bias of the test method (3.10.3), sensitivity analysis
(3.10.4.1), specificity analysis (3.10.4.2), bacterial organism group (3.16);
— Added definition for qualitative test (3.7) and removed definition for breakpoint test;
— Revised definitions for minimum inhibitory concentration test (3.4), breakpoint (3.6), quality
control (3.8), discrepancy (3.10.1).
— Reordered Clause 4 (Test methods);
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SIST EN ISO 20776-2:2022
ISO 20776-2:2021(E)
— Moved general requirements for a performance evaluation as a separate section, to the overview
(now renamed general section, subclause 4.1) under test methods);
— Revised quality control section, subclause 4.2, and referenced EUCAST and CLSI documents for
quality control ranges;
— Revised subclause 4.2.1 (Reference method) to add variability;
— Revised subclause 4.2.2 (Strain selection) and incorporated new definition of contemporary isolates
(3.11.1);
— Revised subclause 4.2.5 (Reproducibility testing);
— Updated subclause 4.2.8 (Discrepancy resolution testing);
— Combined data analysis and acceptance criteria subclauses (Clause 5);
— Revised subclause 5.1 (Accuracy of test device) to remove category agreement;
— Revised data analysis for MIC devices to remove category agreement. Added bias requirement;
— Removed acceptance for breakpoint AST devices;
— Added provisions on acceptance criteria for qualitative AST devices (5.1.3) and included sensitivity
and specificity requirements;
— Revised subclauses on quality control of test device and reproducibility of test device (5.2 and 5.3);
— Revised Bibliography;
— Added Annex A — Evaluation the Performance of MIC Tests, Annex B — Rationale for Bias Analysis,
and Annex C — Sensitivity and Specificity Analyses for Qualitative Tests.
A list of all parts in the ISO 20776 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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SIST EN ISO 20776-2:2022
ISO 20776-2:2021(E)
Introduction
In vitro antimicrobial susceptibility tests are performed on bacteria suspected of causing disease,
particularly if the isolate is thought to belong to a species that can exhibit resistance to frequently used
antimicrobial agents. The tests are also important in resistance surveillance, epidemiological studies of
susceptibility and in comparisons of new and existing agents.
Dilution procedures are used to determine the minimum inhibitory concentrations (MICs) of
antimicrobial agents for antimicrobial susceptibility testing. MIC methods are used in resistance
surveillance, defining and identifying wild type phenotypes, comparative testing of new agents,
to establish the susceptibility of organisms that give equivocal results in routine tests, for tests on
organisms where routine tests can be unreliable and when a quantitative result is required for clinical
management. In dilution tests, bacterial strains are tested for their ability to produce visible growth in
broth (broth dilution) containing serial dilutions of the antimicrobial agent or on a series of agar plates
(agar dilution).
The lowest concentration of an antimicrobial agent (in mg/l) that, under defined in vitro conditions,
prevents the appearance of visible growth of an isolated bacterial strain within a defined period of time,
is known as the MIC. Careful control and standardization are required for intra- and interlaboratory
reproducibility of broth MIC tests. The MICs of quality control (QC) strains generally span three
doubling dilutions with a dominant central value, but can have a four-dilution range.
Broth micro-dilution denotes the performance of the broth dilution test in micro-dilution trays.
Broth micro-dilution is now one of the most common methods used globally to perform antimicrobial
susceptibility tests.
This document is the second edition of ISO 20776-2. It is designed for the evaluation of antimicrobial
test devices against the standard broth micro-dilution reference method (ISO 20776-1) using pure
cultures of aerobic bacteria that are easily grown by overnight incubation on agar and grow well in
standardized micro-dilution trays containing standardized Mueller-Hinton broth (volume of ≤200 µl),
which can need to be modified depending on the antimicrobial agent being tested.
Quantitative MIC and qualitative evaluations detailed in this revised document measure the accuracy,
reproducibility and QC of tests performed with antimicrobial test devices that generate MIC values
against the standard broth micro-dilution reference method. Antimicrobial agar disc diffusion tests are
not included in this document.
This document has been revised using the premise that the MIC test is an in vitro assay, subject to
intra- and interlaboratory assay variation. When making the comparison between any derivative test
and that of the reference method, it is appropriate to apply measures of assay performance only and
not result interpretation. For this reason, and because interpretive categories were removed from the
second edition of ISO 20776-1, categorical agreement (CA) and its associated terminology, as described
by the U.S. Food and Drug Administration (FDA), the Clinical and Laboratory Standards Institute (CLSI)
M23 document, and other international documents, has not been applied. Avoiding an assessment of CA
also assists in reducing the requirement to reassess assay performance automatically when the only
change has been a breakpoint change (which is external to the assay itself).
This document applies to new performance evaluations initiated after the publication date; studies
conducted prior to the acceptance date of this document should not need to be re-designed and/
or re-analysed using these criteria. Studies conducted prior to these standards or acceptance of this
document follow standard practice or guidance at the time of the study.
For derivative tests with more than three two-fold dilutions, assay performance is assessed with tools
designed to measure accuracy using essential agreement (EA) and bias, and precision using EA only. For
derivative tests with 1 to 3 concentrations, assay performance is assessed using standard sensitivity
and specificity measures.
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SIST EN ISO 20776-2:2022
INTERNATIONAL STANDARD ISO 20776-2:2021(E)
Clinical laboratory testing and in vitro diagnostic test
systems — Susceptibility testing of infectious agents and
evaluation of performance of antimicrobial susceptibility
test devices —
Part 2:
Evaluation of performance of antimicrobial susceptibility
test devices against reference broth micro-dilution
1 Scope
This document establishes acceptable performance criteria for antimicrobial susceptibility test
(AST) devices that are used to determine minimum inhibitory concentrations (MIC) of bacteria to
antimicrobial agents in medical laboratories.
This document specifies requirements for AST devices and procedures for assessing performance of
such devices. It defines how a performance evaluation of an AST device is to be conducted.
This document has been developed to guide manufacturers in the conduct of performance evaluation
studies.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 20776-1, Susceptibility testing of infectious agents and evaluation of performance of antimicrobial
susceptibility test devices — Part 1: Broth micro-dilution reference method for testing the in vitro activity
of antimicrobial agents against rapidly growing aerobic bacteria involved in infectious diseases
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
antimicrobial susceptibility test device
AST device
device, including all specified components used to obtain test results that allow MIC determination of
bacteria with specific antimicrobial agents
Note 1 to entry: Specific components of the device include inoculators, disposables and reagents, media used to
perform the test, and readers or analysers. Non-specific components, such as swabs, pipettes and tubes, are not
part of the device.
1
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SIST EN ISO 20776-2:2022
ISO 20776-2:2021(E)
3.2
reference method
method of analysis recognized by experts or used as a reference by agreement between parties, which
gives, or is supposed to give the accepted reference value of the measurand
Note 1 to entry: For the purpose of this document, the reference method described in ISO 20776-1 is employed.
This reference method describes dilution procedures to determine the minimum inhibitory concentration (3.3) of
antimicrobial agents.
[SOURCE: ISO/TS 22176:2020, 3.1.20, modified — Note 1 to entry added.]
3.3
minimum inhibitory concentration
MIC
lowest concentration that, under defined in vitro conditions, prevents visible growth of bacteria within
a defined period of time
Note 1 to entry: The MIC is expressed in mg/l.
3.4
minimum inhibitory concentration test
MIC test
test that is capable of determining a MIC (3.3) covering a range of at least four consecutive doubling
dilutions, and for which essential agreement (EA) (3.10.2) can be determined
3.5
on-scale MIC test result
on-scale minimum inhibitory concentration (MIC) test result
result from a minimum inhibitory concentration (MIC) test (3.4) when there is growth in at least one
dilution below the MIC endpoint and no growth in at least one dilution above
3.6
breakpoint
specific values of parameters, such as MICs (3.3), on the basis of which bacteria can be assigned to
clinical categories such as “susceptible” (S) or “resistant” (R)
Note 1 to entry: For current interpretive breakpoints and interpretive categories, reference should be made to
[2] [3]
the latest publications of organizations employing this reference method (3.2) (e.g. CLSI and EUCAST ).
3.7
qualitative test
test for which the principal objective is to provide a qualitative result
EXAMPLE Using a breakpoint (3.6) or screening concentration.
Note 1 to entry: Such tests have a limited range of 1 to 3 doubling dilutions.
3.8
quality control
QC
use of carefully selected bacterial strains with given expected minimum inhibitory concentration (MIC)
(3.3) results
Note 1 to entry: MICs of antimicrobial agents for control organisms should be within the ranges given in the latest
[2] [4]
editions of the CLSI M100 document or the EUCAST Quality Control document. It is not possible to provide a
single Quality Control Table.
3.9
reproducibility
extent to which consistent results such as MICs are obtained when the test is repeated
3.10 Terms relating to the evaluation of test results
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SIST EN ISO 20776-2:2022
ISO 20776-2:2021(E)
3.10.1
discrepancy
difference in a result between the test method [either a minimum inhibitory concentration (MIC) test
(3.4)] or a qualitative test (3.7)) and the result of the reference method (3.2) outside the region of essential
agreement (EA) (3.10.2) (MIC test), or outside the region of sensitivity and specificity (qualitative test)
3.10.2
essential agreement
EA
minimum inhibitory concentration (MIC) (3.3) result obtained with the antimicrobial susceptibility test
(AST) device (3.1) that is within plus or minus one two-fold dilution step from the MIC value established
with the reference method (3.2)
Note 1 to entry: Used for MIC devices.
Note 2 to entry: Another representation of the concept is:
N
EA
*100
N
where:
N
is the number of bacterial isolates with an EA;
EA
N is the total number of bacterial isolates tested.
Note 3 to entry: The overall EA is expressed as a percentage.
3.10.3
bias of the test method
evaluation of test device results to determine whether the results that differ from the reference method
(3.2) are significantly skewed or predominantly in one direction
Note 1 to entry: Used for minimum inhibitory concentration (MIC) tests (3.4).
3.10.4 Terms relating to sensitivity analysis
3.10.4.1
sensitivity analysis
measure of agreement between test device results and reference
method (3.2) results that are positive or above a published
...
SLOVENSKI STANDARD
oSIST prEN ISO 20776-2:2021
01-julij-2021
Klinični laboratorijski preskusi ter diagnostični preskusni sistemi in-vitro -
Preskus občutljivosti povzročiteljev infekcij in vrednotenje delovanja antimikrobno
občutljivih preskusnih naprav - 2. del: Vrednotenje delovanja antimikrobno
občutljivih naprav (ISO/DIS 20776-2:2021)
Clinical laboratory testing and in vitro diagnostic test systems - Susceptibility testing of
infectious agents and evaluation of performance of antimicrobial susceptibility test - Part
2: Evaluation of performance of antimicrobial susceptibility test devices against reference
broth micro-dilution (ISO/DIS 20776-2:2021)
Labormedizinische Untersuchungen und In-vitro-Diagnostika-Systeme -
Empfindlichkeitsprüfung von Infektionserregern und Evaluation von Geräten zur
antimikrobiellen Empfindlichkeitsprüfung - Teil 2: Evaluation der Leistung einer
Vorrichtung zur antimikrobiellen Empfindlichkeitsprüfung (ISO/DIS 20776-2:2021)
Systèmes d’essais en laboratoire et de diagnostic in vitro - Sensibilité in vitro des agents
infectieux et évaluation des performances des dispositifs pour antibiogrammes - Partie 2
: Évaluation des performances des dispositifs pour antibiogrammes contre méthode de
référence de microdilution en bouillon (ISO/DIS 20776-2:2021)
Ta slovenski standard je istoveten z: prEN ISO 20776-2
ICS:
11.100.10 Diagnostični preskusni In vitro diagnostic test
sistemi in vitro systems
oSIST prEN ISO 20776-2:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 20776-2:2021
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oSIST prEN ISO 20776-2:2021
DRAFT INTERNATIONAL STANDARD
ISO/DIS 20776-2
ISO/TC 212 Secretariat: ANSI
Voting begins on: Voting terminates on:
2021-04-30 2021-07-23
Clinical laboratory testing and in vitro diagnostic
test systems — Susceptibility testing of infectious
agents and evaluation of performance of antimicrobial
susceptibility test —
Part 2:
Evaluation of performance of antimicrobial susceptibility
test devices against reference broth micro-dilution
ICS: 11.100.20
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ISO/DIS 20776-2:2021(E)
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PROVIDE SUPPORTING DOCUMENTATION. ISO 2021
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oSIST prEN ISO 20776-2:2021
ISO/DIS 20776-2:2021(E)
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oSIST prEN ISO 20776-2:2021
ISO/DIS 20776-2:2021(E)
Contents Page
Foreword .iv
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test methods . 5
4.1 General . 5
4.2 Methods . 6
4.2.1 Reference method . 6
4.2.2 Strain selection . 6
4.2.3 Quality control (QC) . 6
4.2.4 Quality control (QC) of the reference method . 7
4.2.5 Reproducibility testing of test device . 7
4.2.6 Isolate testing protocol . 7
4.2.7 Inoculum preparation . 7
4.2.8 Discrepancy resolution testing . 7
4.2.9 System under evaluation . 8
5 Data analysis and acceptance criteria . 8
5.1 Accuracy of test device . 8
5.1.1 General. 8
5.1.2 MIC devices . 8
5.1.3 Qualitative AST devices . 8
5.2 Quality control of test device . 9
5.3 Reproducibility of test device. 9
5.4 Documents related to study . 9
Annex A (informative) Evaluating the performance of MIC tests .10
Annex B (informative) Rationale for bias analysis .13
Annex C (informative) Sensitivity and specificity analyses for qualitative tests .15
Bibliography .17
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oSIST prEN ISO 20776-2:2021
ISO/DIS 20776-2:2021(E)
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 non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 212, Clinical laboratory testing and in
vitro diagnostic test systems.
This document cancels and replaces the first edition (ISO 20776-2:2007), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Revision in the title of part 2 to better align with the intended information;
— Addition of an Introduction – not presented in the original version.
— Revised Terms and Definitions as follows:
— Removed definitions for Category agreement, susceptible, intermediate, resistant, non-susceptible,
major discrepancy, minor discrepancy, very major discrepancy, breakpoint test, zone diameter;
— Added definition for contemporary isolate and removed definitions for fresh isolate, recent isolate;
— Added definitions for reproducibility, bias of the test method, sensitivity analysis, specificity
analysis, organism group;
— Added definition for qualitative test and removed definition for breakpoint test;
— Revised definitions for minimum inhibitory concentration test, breakpoint, quality control,
discrepancy;
— Moved general requirements for a performance evaluation as a separate section, to the overview
(now renamed general section) under test methods;
— Reordered Test methods section;
— Revised quality control section, and referenced EUCAST and CLSI documents for quality control
ranges;
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oSIST prEN ISO 20776-2:2021
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— Revised reference method section to add variability;
— Revised strain selection section and incorporated new definition of contemporary isolates;
— Revised reproducibility testing section;
— Revised discrepancy resolution section;
— Combined data analysis and acceptance criteria sections;
— Revised Accuracy of test device section to remove category agreement;
— Revised data analysis for MIC devices to remove category agreement. Added bias requirement;
— Removed acceptance for breakpoint AST devices;
— Added section for acceptance criteria for qualitative AST devices and included sensitivity and
specificity requirements;
— Revised sections for quality control of test device and reproducibility of test device;
— Revised bibliography;
— Added Annexes A - Evaluation the Performance of MIC Tests, B - Rationale for Bias Analysis, and
Annex C - Sensitivity and Specificity Analyses for Qualitative Tests
A list of all parts in the ISO 20776 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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oSIST prEN ISO 20776-2:2021
ISO/DIS 20776-2:2021(E)
Introduction
In vitro antimicrobial susceptibility tests are performed on micro-organisms suspected of causing
disease, particularly if the organism is thought to belong to a species that may exhibit resistance
to frequently used antimicrobial agents. The tests are also important in resistance surveillance,
epidemiological studies of susceptibility and in comparisons of new and existing agents.
Dilution procedures are used to determine the minimum inhibitory concentrations (MICs) of
antimicrobial agents for antimicrobial susceptibility testing. MIC methods are used in resistance
surveillance, defining and identifying wild type phenotypes, comparative testing of new agents,
to establish the susceptibility of organisms that give equivocal results in routine tests, for tests on
organisms where routine tests may be unreliable and when a quantitative result is required for clinical
management. In dilution tests, micro-organisms are tested for their ability to produce visible growth in
broth (broth dilution) containing serial dilutions of the antimicrobial agent or on a series of agar plates
(agar dilution).
The lowest concentration of an antimicrobial agent (in mg/l) that, under defined in vitro conditions,
prevents the appearance of visible growth of a micro-organism within a defined period of time is
known as the MIC. Careful control and standardization are required for intra- and inter-laboratory
reproducibility of broth MIC tests. The MICs of quality control strains generally span three doubling
dilutions with a dominant central value, but may have a four-dilution range.
Broth micro-dilution denotes the performance of the broth dilution test in micro-dilution trays.
Broth micro-dilution is now one of the most common methods used globally to perform antimicrobial
susceptibility tests.
This document is a revision of a previous ISO document (ISO 20776-2: 2007, Clinical laboratory
testing and in vitro diagnostic test systems — Susceptibility testing of infectious agents and evaluation
of performance of antimicrobial susceptibility test devices — Part 2: Evaluation of performance of
antimicrobial susceptibility test devices). The document is designed for the evaluation of antimicrobial
test devices against the standard broth micro-dilution reference method (ISO 20776-1:2019) using
pure cultures of aerobic bacteria that are easily grown by overnight incubation on agar and grow well
in standardized micro-dilution trays containing standardized Mueller-Hinton broth (volume of ≤200
µl), which may need to be modified depending on the antimicrobial agent being tested.
Quantitative MIC and qualitative evaluations detailed in this revised document measure the accuracy,
reproducibility, and quality control of tests performed with antimicrobial test devices that generate MIC
values against the standard broth micro-dilution reference method. Antimicrobial agar disc diffusion
tests are not included in this revision.
This document has been revised using the premise that the MIC test is an in vitro assay, subject to intra-
and interlaboratory assay variation. When making the comparison between any derivative test and that
of the reference method, it is appropriate to apply measures of assay performance only and not result
interpretation. For this reason, and because interpretive categories were removed from the revision
of the companion document ISO 20776-1, categorical agreement (CA) and its associated terminology,
as described by the U.S. Food and Drug Administration (FDA), the Clinical and Laboratory Standards
Institute (CLSI) M23 document, and other international documents, has not been applied. Avoiding an
assessment of CA also assists in reducing the requirement to reassess assay performance automatically
when the only change has been a breakpoint change (which is external to the assay itself).
This document applies to new performance evaluations initiated after the acceptance date of the
standard; studies conducted prior to the acceptance date of this document may not need to be re-
designed and/or re-analysed using these criteria. Studies conducted prior to these standards or
acceptance of this document follow standard practice or guidance at the time of the study.
For derivative tests with more than 3 two-fold dilutions, assay performance is assessed with tools
designed to measure accuracy using Essential Agreement (EA) and bias, and precision using EA only.
For derivative tests with 1-3 concentrations, assay performance is assessed using standard sensitivity
and specificity measures.
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oSIST prEN ISO 20776-2:2021
DRAFT INTERNATIONAL STANDARD ISO/DIS 20776-2:2021(E)
Clinical laboratory testing and in vitro diagnostic
test systems — Susceptibility testing of infectious
agents and evaluation of performance of antimicrobial
susceptibility test —
Part 2:
Evaluation of performance of antimicrobial susceptibility
test devices against reference broth micro-dilution
1 Scope
This document establishes acceptable performance criteria for antimicrobial susceptibility test
(AST) devices that are used to determine minimum inhibitory concentrations (MIC) of bacteria to
antimicrobial agents in medical laboratories.
This document specifies requirements for AST devices and procedures for assessing performance of
such devices. It defines how a performance evaluation of an AST device is to be conducted.
This document has been developed to guide manufacturers in the conduct of performance evaluation
studies.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 20776-1:2019, Susceptibility testing of infectious agents and evaluation of performance of antimicrobial
susceptibility test devices — Part 1: Broth micro-dilution reference method for testing the in vitro activity
of antimicrobial agents against rapidly growing aerobic bacteria involved in infectious diseases
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
antimicrobial susceptibility test device
AST device
device including all specified components used to obtain test results that allow MIC determination of
bacteria with specific antimicrobial agents
Note 1 to entry: Specific components of the device include inoculators, disposables and reagents, media used
to perform the test, and readers. Non-specific components, such as swabs, pipettes and tubes, are not part of
the device.
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3.2
reference method
reference method described in ISO 20776-1 most recent version. This reference method describes
dilution procedures to determine the minimum inhibitory concentration of antimicrobial agents
3.3
minimum inhibitory concentration
MIC
lowest concentration that, under defined in vitro conditions, prevents visible growth of bacteria within
a defined period of time
Note 1 to entry: The MIC is expressed in mg/l.
3.4
minimum inhibitory concentration test
MIC test
test that is capable of determining an MIC [3.3] covering a range of at least four consecutive doubling
dilutions, and for which Essential Agreement (EA) can be determined
3.4.1
on-scale MIC test result
result from a MIC test [3.4] when there is growth in at least one dilution below the MIC endpoint and no
growth in at least one dilution above
3.5
breakpoint
specific values of parameters, such as MICs [3.3], on the basis of which bacteria can be assigned to
clinical categories such as “susceptible” (S) or “resistant” (R)
Note 1 to entry: For current interpretive breakpoints and interpretive categories, reference should be made to
the latest publications of organizations employing this reference method [3.2] (e.g., CLSI(1) and EUCAST(2)).
3.6
qualitative test
test that has the principal objective to provide a qualitative result (e.g., using a breakpoint [3.5] or
screening concentration)
Note 1 to entry: Such tests have a limited range of 1-3 doubling dilutions.
3.7
quality control of antimicrobial susceptibility tests
quality control includes the use of carefully selected bacterial strains with given expected MIC [3.3] results
Note 1 to entry: MICs [3.3] of antimicrobial agents for control organisms should be within the ranges given in
[1] [3]
the latest versions of the CLSI M100 document or the EUCAST Quality Control document. It is not possible to
provide a single Quality Control Table.
3.8
reproducibility
extent to which consistent results such as MICs are obtained when the test is repeated
3.9
evaluation of test results
3.9.1
discrepancy
difference in a result between the test method (either a MIC test [3.4] or a qualitative test [3.6]) and
the reference method [3.2] (ISO 20776-1) outside the region of essential agreement (MIC test [3.4]), or
outside the region of sensitivity and specificity (qualitative test [3.6])
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3.9.2
essential agreement
EA
MIC [3.3] result obtained with the AST device [3.1] that is within plus or minus one two-fold dilution
step from the MIC [3.3] value established with the reference method [3.2] (ISO 20776-1)
Note 1 to entry: Used for MIC [3.3] devices.
Note 2 to entry: Another representation of the concept is:
N
EA
×100 , where:
N
N is the number of bacterial isolates with an EA;N is the total number of bacterial isolates tested
EA
Note 3 to entry: The overall EA is expressed as a percentage.
3.9.3
bias of the test method
evaluation of test device results to determine whether the results that differ from the reference method
[3.2] are significantly skewed or predominantly in one direction
Note 1 to entry: Used for MIC tests [3.4].
3.9.4.1
sensitivity analysis
measure of agreement between test device results and reference
method [3.2] results that are positive or above a published breakpoint [3.5] Can also be considered as
positive percent agreement when reference results are interpreted as positive
Note 1 to entry: Used for qualitative tests [3.6].
Note 2 to entry: See Table 1 .
Table 1 — Sensitivity analysis for a qualitative (screening or breakpoint) test
Reference method
Total
(-) or no growth (+) or growth
(-) or no growth a b a+b
Test method
(+) or growth c d c+d
Total a+c b+d Sum of (a,b,c,d)
Sensitivity = 100×÷db()+d
[]
3.9.4.2
sensitivity analysis
measure of agreement between test device results and reference
method [3.2] results that have the MICs [3.3] at the high end of the scale
Note 1 to entry: Used for qualitative tests [3.6].
Note 2 to entry: See Table 2 .
Table 2 — Sensitivity analysis for a three-dilution qualitative test
Reference method
Total
≤ Low MIC Middle MIC ≥ High MIC
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Table 2 (continued)
≤ Low MIC a b c a+b+c
Test method Middle MIC d e f d+e+f
≥ High MIC g h i g+h+i
Total a+d+g b+e+h c+f+i Sum of (a to i))
Sensitivity = 100×÷ic()++fi
[]
3.9.5.1
specificity analysis
measure of agreement between test device results and reference
method [3.2] results that are negative or below a published breakpoint [3.5] Can also be considered as
negative percent agreement when reference results are interpreted as negative
Note 1 to entry: Used for qualitative tests [3.6].
Note 2 to entry: See Table 3 .
Table 3 — Specificity analysis for a qualitative (screening or breakpoint) test
Reference method
Total
(-) or no growth (+) or growth
(-) or no growth a b a+b
Test method
(+) or growth c d c+d
Total a+c b+d Sum of (a,b,c,d)
Specificity = 100×÷aa()+c
[]
3.9.5.2
specificity analysis
measure of agreement between test device results and reference
method [3.2] results that have the MICs [3.3] at the low end of the scale
Note 1 to entry: Used for qualitative tests [3.6].
Note 2 to entry: See Table 4 .
Table 4 — Specificity analysis for a three-dilution qualitative test
Reference method
Total
≤ Low MIC Middle MIC ≥ High MIC
≤ Low MIC a b c a+b+c
Test method Middle MIC d e f d+e+f
≥ High MIC g h i g+h+i
Total a+d+g b+e+h c+f+i Sum of (a to i))
Specificity = 100×÷aa()++dg
[]
3.10.1
contemporary isolate
isolate recovered from a clinical sample within the previous six months that has been minimally sub-
cultured
Note 1 to entry: Ideally, they are consecutive and prospectively collected. These isolates can have been frozen
prior to use.
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3.10.2
stock isolate
isolate recovered from a clinical sample that has been retained, stored or obtained from a culture
collection
Note 1 to entry: Stock isolates are usually included because they have known or rare resistance mechanisms
or are of a genus or species for which the antimicrobial agent is indicated but are not commonly isolated. Such
organisms are unlikely to be available in contemporary isolates used in the evaluation. There is no requirement
for how long ago the isolate was obtained.
3.11
coordinator
person empowered by the manufacturer or investigator [3.12] with responsibility for the entire
performance evaluation
3.12
investigator
person responsible for the execution of the performance evaluation at a certain location
3.13
evaluation plan
description of a planned performance evaluation
3.14
evaluation report
description of and conclusions from a performance evaluation
3.15
organism group
group of related micro-organisms that share similar characteristics
4 Test methods
4.1 General
The manufacturer or investigator takes the responsibility for the initiation and the conduct of
a performance evaluation according to the evaluation plan. The manufacturer shall define the
responsibility and the interrelation of all personnel who manage and conduct a performance evaluation.
The manufacturer or investigator shall appoint a coordinator with overall responsibility for the
performance evaluation and the evaluation report. This may include a coordinator, who shall assess
and document criteria used and indicate which performance claims are met.
An evaluation conducted by a manufacturer shall consist of accuracy using contemporary and stock
strains, reproducibility and quality control testing performed in at least three different laboratories,
of which a maximum of one may be the manufacturer's laboratory. Alternatively, these studies may
be conducted at a single site that mimics three sites (e.g., multiple users/instruments, geographically
diverse source of organisms. This single site may be within the manufacturer’s laboratory. The complete
testing protocol should focus on the m
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