Terminology Extensions: What They Are And Why Develop One?
What are Terminology Extensions?
Terminology extensions are used to expand upon the content that is produced by Standards Development Organizations (SDO). Only a few terminologies provide support for extensions within their native data structures. Those that do not provide support for extensions can still be extended using local data structures.
Why are Terminology Extensions Needed?
The best outcome when recording patient data is to represent exactly what you are observing or performing. However, even with the large standard terminologies, such as SNOMED CT, there may remain healthcare information that is not represented. There are a wide array of reasons for this to be the case. The main ones are:
The information may never be able to be represented in the standard due to resource constraints within the standards development organizations (SDO)
Need for the data recorded faster than can be expected to be adopted by the SDO
Is unique to a specific institution (whether public or private)
May be various ways to represent the information while a single institution may elect to utilize a specific one
Desire to focus at a deeper level than available such as for research purposes
Generalizing, or opting to record data with a broader meaning can be good in certain use cases and is what you do in the case of using a billing or classification system like ICD-10. This strategy does not accurately represent patient data and will lead to a loss of meaning over time because the original meaning is not preserved.
How are Terminology Extensions implemented within a Terminology Server/Terminology Browser?
A good terminology server and terminology browser will make the display and use of a terminology extension almost invisible to the user. The content that must be made available is any metadata or extension specific attributes that the terminology extension contains. Terminology servers and terminology browsers treat extensions the same as the base terminology and essentially just add the extension on top. For example, the US Extension of SNOMED is added on top of SNOMED Core. Likewise, the VA Extension of SNOMED is added on top of the US Extension of SNOMED.
See our Terminology Browser at https://snomed.westcoastinformatics.com/ for examples of the SNOMED CT US Extension. If you search for “Chronic viral hepatitis C with hepatic coma” you will see an example of an Extension concept.
What are the most popular terminologies that have a defined mechanism for Extension Support?
A number of terminologies have an established mechanism for creating extensions. Amongst them are:
SNOMED CT: Has an official extension mechanism in place. For more information, see <link>
ICD-10: Countries are able to extend ICD-10. For example, the United States (through the National Library of Medicine) has extended ICD-10 into ICD-10-CM and ICD-10-PCS. Meanwhile, Canada (through Canadian Institute for Health Information) has extended ICD-10 into ICD-10-CA.
What are the different types of Extensions?
There are a couple of options for accurately representing patient data and each of them have their strengths and weaknesses. These include building your own local code system, creating an extension to an existing standard, or using something called post-coordination. The different types of extension are:
Official Standard/National Release Center (NRC) extensions: Extensions that are created by Standards Development Organizations (SDOs) or National Release Centers are typically developed to create and support content that is used or is specific to a nation or specific domain. Examples of this type of extension would be the various national extensions of SNOMED CT or ICD-10-CM which is a clinical modification of the WHO version of ICD-10 which is used within the US.
Local extensions: Even with the original content created by the terminology developer and the National/SDO extensions there still may be the need to create content locally. Kaiser Permanente has created and maintained an extension to SNOMED CT since the first release of SNOMED CT.
What is a Local Extension?
Local extensions are extensions that are created by organizations that need content for a specific use case that may not apply in a national or international context. Local extensions may also be used for content that is needed quicker than it can be added nationally/internationally.
What is a Standard/National Release Center (NRC) Extension?
Standard/National Release Center extensions are produced by International or National organizations that develop extensions to support some specific national or domain specific use case.
What information can be added to a Terminology Extension?
What you can author in an extension depends on the standard you are trying to extend and what they allow or provide. Standards like SNOMED CT fully support your ability to create extensions whereas others are not as supportive and may require permission before you begin.
Descriptions: Sometimes you are not missing a concept, you are just wanting to call one by a different name. If it is synonymous, then adding a description to an existing concept is an easy task and something that doesn’t take a lot of time to maintain with each new release.
Reference Sets/Value Sets: Reference Sets and/or Value Sets are collections of concepts or descriptions that are meant to be used for a particular purpose. For example, a set of concepts that are used within a specific field in a record.
Mappings: Allow you to translate a concept in one terminology into another concept in a different terminology or coding system. If you wish to change an existing mapping or add new mappings an extension would allow you to make these changes.
Concepts: This component of an extension can be the most difficult to create and maintain. If concepts are urgently needed then having an extension allows you to add it for immediate use. The other option would be to submit for inclusion in the national or international standard, but this may take months or years. Adding concepts are made difficult due to the fact that you will need to detect equivalent concepts to ensure you are not adding a duplicate concept. You will also need to verify it meets the concept model of the standard you are extending.
Relationships: If there are errors found within the standard or an extension you could update the relationships to correct the issue until a fix can be made. Since terminologies can sometimes take months to fix and release reported issues, making a change in an extension to allow for the correct use of relationships are important to allow accurate retrieval of information.
When would you extend a Terminology's Concepts?
If the terminology is missing a concept that you need to record patient data then adding a concept in an extension would be appropriate. This typically requires the addition of descriptions and relationships for those terminologies that require them.
When would you extend a Terminology’s Descriptions?
Missing synonymy is a common use case for terminology extensions. The ability of standards organizations to add all of the required synonyms for concepts they maintain is limited.
When would you extend a Terminology's Relationships?
This is most commonly done in conjunction with the addition of a new concept. However, if an error is noticed while using a concept from a terminology, corrections to the relationships could be made in an extension. This should be done in rare instances and would be best reported to the SDO for correction.
When would you extend a Terminology's Mappings?
Terminology mappings from an SDO or National Release Center may not always match what the end user wishes to map to. If you need to change an existing mapping or add new mappings an extension would allow you to make these changes.
When would you extend a Terminology's Reference Sets/Value Sets?
Reference sets/value sets from an SDO or National Release Center may not always match the needs of your organization. These can be customized using an extension by either adding or removing content.
How can you extend Terminology Standards?
Depending on the size and complexity of the extension you are trying to create, you will want some form of tools and processes to manage the changes that will be needed over time. There are a few things that you can use to help you maintain them:
Spreadsheets: Doing something small can certainly be done using spreadsheets. Adding your own Descriptions, small reference sets, small changes and additions to mappings can easily be handled via a spreadsheet. This method of creating and maintaining spreadsheets would quickly become cumbersome and migrating to some form of tooling would become a priority.
Proprietary Tooling: A variety of tools allow you to extend terminology but may not support. Not all proprietary tools perform all the Extension tasks you may need to easily maintain the content you are developing.
SDO Tooling: While not available to everyone nor for all terminologies, SDO’s like SNOMED International provide a suite of tooling for National Release Centers that wish to create a national extension.
What are the Benefits in Using Terminology Extensions?
There are great benefits to using terminology extensions. They are:
More Control of Your Data
Having an extension allows you to add new synonyms and preferred ways of naming existing concepts. This gives you more control over how you describe things. You can also then map them to other standards in a way that best works for your use cases.
Better Data Reuse
Having more control of your data representation leads to better reuse of your data because you know exactly what was observed or performed. As terminologies change and evolve over time you will also know that the data you recorded was accurate at the time and won’t lose its original meaning.
What are the Risks When Using Terminology Extensions?
There are a variety of risks involved when using a terminology extension. A few of them include:
Content Quality Issues
Adding content, especially concepts, require extensive knowledge of how the standard terminologies are created, maintained, and intended to be used. This includes in-depth knowledge of the concept model used to create the concepts.
In complex terminologies like SNOMED CT, you need to ensure that you have appropriately and completely placed the new concept within the correct hierarchies. This should involve using a description logic classifier to detect new relationships and eliminate redundant ones.
To ensure that the content you add is done correctly you should utilize quality assurance checks to ensure you are not introducing errors within the extension. Nothing kills an application faster than a good cycle error. Using an extension that is external to your organization doesn’t guarantee that it is free of quality issues. You should do your own evaluation of the content before you begin to use it.
Interoperability Difficulties
Exchanging data may be more difficult if everyone creates their own extensions. If the organizations you are communicating with do not have access to your extension the data you are exchanging may not be reusable.
Never-Ending Maintenance
Every time a standard terminology that you have built your extension off releases an update you will need to determine whether you will process that release and make the necessary changes to your extension. Types of changes include:
New concepts that may need to replace your content.
Retired concepts that could have been used to model your concepts.
Changes to hierarchies that could require changes to your concepts (new parents, removed parents).