The technical stages of the establishment of a new standardized reference method or the revision of an existing standardized reference method have been described in standard ISO 17468.
Validation required after revision depends on the nature of the changes in the method.
Learn more about ISO 17468, major and minor changes and their impact.
A new edition of ISO 17468:2023 ‘Microbiology of the food chain – Technical requirements and guidance on the establishment or revision of a standardized reference method’ has been recently published. This International Standard sets common rules for the validation of reference methods standardized in the field of microbiology of the food chain by ISO/TC 34/SC 9 and its corresponding structure at European level (CEN/TC 463 ‘Microbiology of the food chain’). It defines the technical stages of the establishment of a new standardized reference method or the revision of an existing standardized reference method in International Standards.
Six technical stages may be followed for the validation of a method in its standardization process as a reference method, the last one consisting of an interlaboratory study (ILS). The values of performance characteristics of the method are derived from these ILS data. The experimental design and calculation of the performance characteristics in the different stages are cross-referenced to the appropriate part of the ISO 16140 series.
Major/minor changes in the revision of International Standards
Validation required for the revision of an existing International Standard, i.e. a standardized reference method, depends on the nature of the technical changes in the method, whether they are minor or major. A major technical change is, for example, a modification in the method detection or quantification technology or a substantial modification of the procedure (e.g. nature of the enrichment broth or isolation agar, incubation time or temperature). It is expected to produce a different result. An example for a major technical change is shown in ISO 21528-1:2017, ISO 22964:2017 or ISO 10273:2017. A minor change is, for example, an editorial change to the text of the method or a minor technical change that is not expected to affect the result. An example of a minor technical change is shown in the ISO 10272 series for the detection and enumeration of Campylobacter spp., where the confirmation tests on microaerobic growth at 25 °C and aerobic growth at 41,5 °C were replaced by aerobic growth at 25 °C.
If the technical change in the method is evaluated as being major, a re-validation of the method is needed. When the re-validation of the method is conducted, the impact on the performance characteristics shall be evaluated to determine if the changes are to be regarded as major (performance characteristics have substantially changed) or minor (no impact on performance characteristics observed). In certain cases, a major technical change in the method can be considered to be minor, if the re-validation of the method shows that it has no significant impact on the performance characteristics or test results. An example for a major technical change considered as minor is shown in the ISO 11290 series for the detection and enumeration of Listeria monocytogenes and of Listeria spp.
Upon revision of a standardized reference method, a statement on the changes made (minor or major and with or without impact on performance characteristics) is to be included in the introduction of the revised International Standard.
More information on (proprietary) method validation and method verification can be found here.
Main changes in ISO 17468
ISO/TC 34/SC 9/WG 3 ‘Method validation’ has recently finalized the revision of ISO 17468 from 2016. The main changes in ISO 17468:2023 are as follows:
• Clarification on which steps are mandatory [method(s) selection, selection of one candidate reference method for further validation and interlaboratory study] or recommended/optional [method(s) optimization, method(s) evaluation study and “real life” study].
• A new optional step has been added, “method(s) optimization”. In addition, a new annex providing guidance on method optimization studies is included, to compare two options during the development of a new standardized reference method or for its revision.
• Inclusion of the case of confirmation and typing methods.
• A cross-reference in the different steps is made not only to ISO 16140-2, but also to ISO 16140-4 and ISO 16140-6.
• The assessment of the nature of a change (minor/major) during the revision of a standardized reference method has been included.
• To provide guidance and templates on the drafting of the clauses of standardized reference methods on validation data, a reference has been added to the document: Microbiology of the food chain — Template and guidance for drafting ISO/CEN standards, 3rd edition.