Background

SNOMED CT is a clinical terminology with a global scope covering a wide range of clinical specialties and requirements. Each concept in SNOMED CT represents a clinical idea to which a unique concept identifier has been assigned. Some concepts represent atomic, or simple, meanings, such as  |Edema (finding)| , or |Foot structure (body structure)| , while other concepts represent more complex clinical meanings, such as |Atypical mycobacterial infection of lung (disorder)| , or |Positron emission tomography with computed tomography of heart (procedure)| . SNOMED CT concepts are also referred to as precoordinated concepts or Precoordinated expression.

Aside from the unique concepts, meanings can also be represented in SNOMED CT through postcoordinated expressions, which are structured combinations of two or more concept identifiers. The ability of SNOMED CT to support postcoordination is important because it enables a wide range of clinical meanings to be captured in a record, without requiring the terminology to include a separate concept for every detailed combination of ideas that may potentially need to be recorded. Thus, postcoordination greatly increases the depth of detail that SNOMED CT can represent, while avoiding a combinatorial explosion of precoordinated concepts. The SNOMED CT concept model provides the rules for the kinds of relationships that can be specified between particular types of concepts when creating postcoordinated expressions.

Objective and Scope

The objective of this guide is to provide a practical point of reference for the best practice principles for enabling postcoordination with SNOMED CT.

The chapters of this guide aim to answer the following questions:

• What characterizes a postcoordinated expression?
• What are the use cases for postcoordination?
• What are the prerequisites for enabling postcoordination?
• What approaches can be taken to enable postcordination in an Electronic Health Record?
• What are the steps involved in the creation, implementation, and use of postcoordinated expressions?
• What is required by a terminology server designed to support postcoordination?

Status

The guide is intended to provide an overview of the preliminary work done to facilitate the safe use of postcoordination with SNOMED CT within Electronic Health Records. It offers guidance on the best practices and considerations for implementing postcoordination effectively, and outlines potential risks and benefits associated with this approach. We encourage initiatives to follow the implementation approaches outlined in this guide on a trial basis to evaluate their effectiveness and suitability for your specific use case.

The document is a dynamic resource, and it will continue to advance as implementation experience and maturity expand. Its content will be regularly updated to reflect the latest advancements and insights in the domain. Users are encouraged to utilize this guide as a source for continuous learning and enhancement of their use of SNOMED CT and postcoordination.

Out of Scope

This document presents the design and technical implementation of an expression repository and terminology services required when enabling postcoordination in an EHR. However, some areas are not included in the current version, as they are still under investigation and will be added in the future as knowledge and experience in this are increase.

The does not offer detailed maintenance documentation for the expression repository, and implementing postcoordinated expressions in a production environment, therefore, requires careful analysis and establishment of required processes. The guide also lacks information on governance structures, work processes, and clinical validity beyond the rules specified in the Machine Readable Concept Model. Therefore, anyone attempting to support postcoordination in their EHR should follow the editorial guidelines to ensure logical consistency and clinical meaningfulness of meanings expressed through SNOMED CT.

Audience

This guide is targeted towards SNOMED CT Members and Affiliates who are involved in the creation, implementation, and maintenance of postcoordinated expressions.

• People involved in the design and development of SNOMED CT enabled solutions
  • This includes designers and developers of EHR systems, information models, data entry interfaces, storage systems, decision support systems, retrieval and analysis systems, communication standards, and terminology services

Document Overview

This document presents a practical guide to postcoordination with SNOMED CT and is structured as follows:

• 1. Introduction: This chapter explains the background, purpose, scope, audience and overview of the document
• 2. SNOMED CT Expressions: This chapter introduces SNOMED CT expressions, describing the syntax, structure and forms of expressions. It also outlines the benefits, challenges and considerations associated with the decision to support postcoordinated expressions
• 3 System Components: This chapter introduces the components included in the design of systems enabled to support postcoordination
• 4. Expressions in the EHR: This chapter introduces and exemplifies how expressions may be used within an Electronic Health Record to support key tasks including clinical data entry, storage, display, exchange and retrieval
• 5. Expressions in a Terminology Server: This chapter describes the requirements and design of a terminology server supporting postcoordination. It introduces various levels of implementations that have been specified to ensure the safe implementation of postcoordination, and it documents how the design can be met complying with RF2 or HL7 FHIR

Feedback

We invite SNOMED CT Members and Affiliates to try this initial version of the guide. It will be extended and enhanced following feedback. Please send any comments or questions to info@snomed.org.