SNOMED CT (Systematized Nomenclature of Medicine – Clinical Terms) is the most comprehensive and precise multilingual clinical health terminology used all over the world. There is an international organization, called SNOMED International, that owns and maintains the terminology, and like the International Classification of Diseases, Tenth Revision (ICD-10), there is an U.S. extension of it.

NLM is the U.S. National Release Center for SNOMED CT. NLM creates the US Edition of SNOMED CT, which is a combination of the U.S. extension of SNOMED CT and the SNOMED CT International Edition. NLM oversees licensing of users in the United States, helps make the latest releases of SNOMED CT available to U.S. users, and represents the U.S. in international discussions about SNOMED CT. If you are in the United States, you should visit the NLM SNOMED CT website to download the US Edition of SNOMED CT.

SNOMED CT has been designated as a national standard for several purposes (including problem list and public health reporting) in the initial certification criteria for EHRs issued by ASTP/ONC.

Activity

You can see how SNOMED CT is used in EHR systems via this SNOMED CT Search demo. SNOMED CT has been implemented in this demo EHR system.

Start typing Chest pain in the "Reason for Encounter" field and select the term.

Start typing Myocardial infarction in the "Diagnosis" field and select the term.

Start typing Electrocardiographic procedure in the "Procedure" field and select the clinical term.

You are querying the SNOMED CT data and selecting a SNOMED CT concept. SNOMED CT codes are associated to each of these concepts and allow for interoperability between different healthcare providers and systems.

For demo purposes only, after you save the selected concepts and create an entry in the Encounter History, you can hover over the concepts to see the associated SNOMED CT codes.

Below is an example of an entry documenting a diagnosed myocardial infarction (heart attack), showing the SNOMED CT code (22298006).

The hundreds of thousands of concepts in SNOMED CT are organized into a multi-axial hierarchy. Also, there are defining attributes assigned to a concept, such as IS A relationships, that are used to determine where in the hierarchy the concept is placed and to create a logical definition.

Here is an example of how SNOMED CT concepts use these defined attributes to create a logical definition. This diagram shows the logical definition for the concept Myocardial infarction. It is an Ischemic heart disease and it is a Myocardial necrosis; hence, the multi-axial hierarchy. Myocardial infarction also has a finding site of Myocardium structure and an associated morphology of Infarct. Knowledge can be embedded in SNOMED CT through these links. This representation provides significant power for queries by any of these relationships.

In addition to predefined relationships, there will be times when a condition or concept isn’t an existing concept in SNOMED CT but could be created from existing terms. When a term is entered into the system as its own unique code, it is called a pre-coordinated term. When it is created from other codes, it is called a post-coordinated term.

Here is an example of a post-coordinated term:

SNOMED CT support of the post-coordination technique allows additional clinical detail to be represented if required. Post-coordination greatly increases the depth of detail that SNOMED CT can represent without having to include every possible specific site for every possible disorder via a concept.

For example, the concept |bacterial pneumonia| has a defining relationship specifying its |causative agent| as |bacteria| and this can be refined to |streptococcus pneumoniae|.