This section provides an overview of:

Why is this important?

Clinical information recorded using SNOMED CT may include data that is relevant to reports, statistical returns, billing claims, etc. that need to be encoded using a specific code system or a statistical classification such as ICD-10. Mapping allows relevant information to be used for those purposes, minimizing the requirement for additional manual data entry.

Organizations planning to implement SNOMED CT based solutions may also be faced with data transformation and migration challenges which lead them to consider mapping their existing clinical data, code systems or classifications to SNOMED CT.

As a common global reference terminology, SNOMED CT limits the need for development of "everything to everything" maps between multiple different code systems.

Problem: Map Everything to Everything

Solution: Map to a SNOMED Clinical Terms


What is this?

Maps are associations between particular codes, concepts or terms in one code system and codes, concepts or terms in another code system that have the same (or similar) meanings. Mapping is the process of defining a set of maps. Maps are developed in accordance with a documented rationale, for a given purpose and as a result there may be different maps between the same pair of code systems to meet different uses cases.

There are a number of different types of mapping activities that an organization may need to undertake. These include mapping:

The completeness of mapping between two code systems depends on the scope, level of detail provided by the two schemes and the precision of mapping required to safely meet the intended mapping use case.

Mapping Approaches

The approaches used when undertaking mapping include human mapping, automatic mapping or a combination of both of these.

Automatic mapping is when computer algorithms are used to create maps between concepts and or terms - for example between local clinical content and SNOMED CT. Lexical mapping, where the structure of the words in the clinical term is compared and analyzed as to whether the words are the same, similar or different, is often incorporated within automatic mapping. Significant care must be taken with automatic mapping, because severe mapping errors can result if not done in a controlled way. Automatic mapping, in conjunction with human review (and manual remapping where necessary), is likely to achieve better results than automatic mapping alone.

Human mapping is the use of human knowledge and skill to author maps. Each map is built singly and individually. The process requires examination of each and every concept in the coding system. Informed judgments or decisions are made about the shared meaning of concepts. Electronic or computational tools are used, but only in support of work process.

How SNOMED CT Represent Maps

SNOMED CT specifications and content include resources that support mapping to and from other code systems, classifications and terminologies. These resources support simple, complex and extended mappings. Simple maps, where there is a one-to-one Relationship between a SNOMED CT concept and code in a target scheme, are represented using a Simple Map Reference Set. Complex and Extended Map Reference Sets enable the representation of:

Steps in a Mapping Process

The main steps to be completed and documented when completing a mapping process include:

Evaluating Mapping as a Solution

When approaching the creation of a map, the first step is to understand the data which needs to be transformed or migrated and the requirements for use of that data. Key questions to address include:

Produce Mapping Requirements

It is essential to fully understand the structure, content and semantics of both the source and target code systems. It is also important to understand how the meaning of the codes is affected by the structure and functionality of the source and target systems. Once the code system and how it has been used is fully understood, a document should be created which defines the rules to be applied when creating maps to or from SNOMED CT. These rules will address for example, the approach to inexact mappings, the use of synonyms, postcoordinated expressions and others. In order to be able to understand the evolution of the maps, an audit trail of the map creation and maintenance activity should be maintained.

Human resource requirements are dependent on the mapping scale, the model used for mapping and the type and complexity of the map being developed. The roles that may be required could include mapping sponsor, mapping manager, mapping specialist, clinical specialists and a mapping advisory group.

Once all requirements have been defined, appropriate software tools to support the creation of the maps must be decided upon. The tools required depend on the complexity of the map and mapping process. Three main alternatives include the use of simple multipurpose tools like Excel, dedicated map maintenance applications and/or custom built applications.

Develop the Map

The process of map development needs to be done in a controlled manner and involves:

Checks and balances should be used at each stage to ensure that the process is technically accurate and any maps created should be checked either using a map verification process or by parallel independent mapping. Once maps are created and published a cycle of testing should be performed to validate that the results obtained through the use of the maps to transform or migrate data meets the defined requirements.

Use the Maps

Having created the maps to or from SNOMED CT, there are various aspects to consider when using the maps to migrate or transform clinical data. The actual specific use case needs to influence the final requirements of how this is undertaken. Specific attention needs to be paid to reporting, interoperability and data migration. The more common use cases are:

Throughout the use of maps, there are fundamental principles and best practices that should be adhered to including:

Review Activity

As with any process, a post-activity review stage is recommended. This should ensure that: