# Do I need an external interface terminology to implement SNOMED CT? *Collection: Implementation dilemmas* **Summary**: No, as a general approach, SNOMED CT does not require an external interface terminology to be implemented in clinical settings. SNOMED CT descriptions function as interface terminology, and clinical projects in member countries submit requirements and updates to improve this resource's quality continuously. *** ## Implementation dilemma Some SNOMED CT implementers consider whether it is necessary to use an external interface terminology, i.e., a list of clinical terms specially designed to facilitate data entry. Each term would be mapped to SNOMED CT. The goal of using custom interface terminology is to have more control over the terms presented to the user, intending to provide a better fit for the local context. ### What's an external interface terminology? Custom interface terminologies offer a separate set of terms that can match user search strings and are directly mapped to SNOMED concepts. These custom terminologies can include terms that do not adhere strictly to SNOMED naming conventions, such as local terms, jargon, typos, etc. Maintaining a custom interface terminology requires great effort and dedication to keep current and ensure the best quality. To what extent is a custom interface terminology required when integrating SNOMED CT into clinical systems? ## Advice The recommended approach in modern SNOMED CT implementations is to use SNOMED descriptions as the interface terminology. The separation of "interface" and "reference" terminology roles has been reviewed in many articles[1](#references), where the interface terminology is used to collect information, and the Reference Terminology is used to represent the information with the greatest possible level of detail and its relationships to other concepts. An antecedent version of SNOMED from 1997 was denominated SNOMED RT (Reference Terminology), describing the intended role of that version of the terminology. However, the next generation of SNOMED terminologies, the one we use today, was released in 2001 and includes specially designed interface terminology functions. Today, SNOMED CT is implemented worldwide using its native interface terminology features for data entry without requiring an external interface terminology. The June 2024 International Edition contains 1.6 million active descriptions for 368,000 active concepts, averaging 4.4 descriptions per concept[2](#references). SNOMED terms have a clinical level of detail, including wording as submitted by clinicians in member countries. Members and affiliates can add additional terms as required in national or local extensions. Using best practice text matching algorithms supports partial matching and meaningful sorting, which facilitates clinicians' search by parts of clinical terms. The best matches are properly shown first in the results, facilitating identification and selection. Clinicians can search for SNOMED CT concepts using text searches that match the descriptions provided in the International Edition or any SNOMED Extension.

Table 1: Example of native SNOMED CT interface terminology features

| Concept Id | Term | Description ID | | ---------- | ---------------------------------------------------- | -------------- | | 22298006 | Myocardial infarction (disorder) | 751689013 | | | Myocardial infarction | 37436014 | | | Cardiac infarction | 37442013 | | | Heart attack | 37443015 | | | Infarction of heart | 37441018 | | | MI - myocardial infarction | 3726632018 | | | Myocardial infarct | 1784873012 | | 406506008 | Attention deficit hyperactivity disorder (disorder) | 2150336014 | | | Attention deficit hyperactivity disorder | 2158158016 | | | ADHD - Attention deficit disorder with hyperactivity | 2163260014 | | | Attention deficit hyperkinetic disorder | 2163265016 | | | Hyperkinetic disorder | 2163261013 | | | Hyperkinetic syndrome | 2163262018 | | | MBD - Minimal brain dysfunction | 2163266015 | | | Minimal brain dysfunction | 2163263011 | | | Overactive child syndrome | 2163264017 | Custom interface terminologies are usually incomplete and map only to a part of SNOMED CT. They are challenging to maintain and keep up to date with new SNOMED versions, with risks of quality issues like duplication and ambiguity. Users who access SNOMED content through interface terminology will experience the continuous improvements and enhancements published monthly in SNOMED releases only when those are reflected in the custom terminology. The SNOMED release is prepared to be imported into standard terminology servers supporting effective search engines. Maintaining additional synonyms as part of an extension of SNOMED CT provides many benefits for seamless integration with SNOMED updates and integrations in clinical systems. Local or custom interface terminologies can play a role in migrating systems to SNOMED CT. Some systems may need more flexibility to incorporate full use of standard terminology services, or the clinical user base could be inclined to continue coding with a local set of terms. However, it is recommended that this be an interim solution until the system is upgraded to support full access to SNOMED CT content directly, unlocking the complete breadth of content in SNOMED CT for data entry. Modern SNOMED CT is a global collaborative terminology system with over 50 member countries actively contributing to its development. These countries prioritize development areas, submit new content, and shape a unified health language. Accessing SNOMED CT content solely through an external interface terminology will restrict access to continually updated content and ongoing improvements. ### Tips for best results implementing direct data entry with SNOMED CT * Focus on creating the best possible terminology bindings: use value sets or ECL (the Expressions Constraint Language) to ensure that only the right concepts are available for data entry * Use a terminology server for out-of-the-box best-practice text-matching algorithms or implement these algorithms locally[3](#references) * Train clinical users on how the multiple prefixes, no order, string matching technique works. * Include local synonyms as new descriptions on a local extension, or submit synonyms requests to national or international editions. * Consider the use of a local synonyms table for pre-normalization of search terms. * Implement advanced NLP or AI matching to compensate for spelling errors ("Did you mean...?) *** ## References 1. Rosenbloom ST, Miller RA, Johnson KB, Elkin PL, Brown SH. Interface terminologies: facilitating direct entry of clinical data into electronic health record systems. J Am Med Inform Assoc. 2006 May-Jun;13(3):277-88. doi: 10.1197/jamia.M1957. Epub 2006 Feb 24. PMID: 16501181; PMCID: PMC1513664. 2. SNOMED Release Statistics: 3. ## Learn More To learn more, please reach out to . Provide Feedback --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.snomed.org/implementation-guides/implementation-fact-sheets/implementation-dilemmas/do-i-need-an-external-interface-terminology-to-implement-snomed-ct.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.