SNOMED CT-AU descriptions

Descriptions are human readable names (text strings) that describe a clinical concept in SNOMED CT-AU. There are two description types in SNOMED CT-AU:

  1. Fully Specified Name (FSN);
  2. Synonym – of which there are 2 subtypes;
    1. Preferred synonym (commonly known as the Preferred Term); and
    2. Acceptable synonym.

Every concept must have one FSN and one Preferred Term. Therefore, each description has a unique description id but shares the same concept id with other descriptions that describe the same concept.

What is the purpose of the different description types?

Fully Specified Name
e.g. Myocardial infarction (disorder)

The FSN is the full, unambiguous description for a concept. Each FSN is a unique text string and contains a semantic tag (bracketed words at the end of a description), that indicates the hierarchy in which the concept is located.

The FSN is not recommended for use as the display term at the user interface, as it can be wordy, may include all the attributes of a concept, and may not be the recognised term for use in Australia.

Preferred Term
e.g. Myocardial infarction

The Preferred Term is the preferred way of naming the concept in Australian healthcare settings and is recommended as the display term at the user interface. NCTS terminologists curate these terms according to country specific language variants, recognised usage, relevancy and clinician feedback.

The Preferred Term is unique within a given SNOMED CT-AU hierarchy but may not be unique across different hierarchies.

Acceptable Synonym
e.g. Cardiac infarction, Heart attack, Infarction of heart, MI – myocardial infarction, Myocardial infarct

Acceptable synonyms are alternative ways of naming the concept, which are acceptable for use in Australian healthcare settings. A concept may have none or several of these.

Acceptable synonyms are usually implemented together with the Preferred Term in a product’s search function, to support different ways a user might search for the same concept e.g. “MI” and “Heart attack” are common ways to search for “Myocardial infarction”.

Uniqueness of descriptions within a hierarchy

Preferred and acceptable synonyms can have identical text but the concepts they describe (link to) must be unique to avoid ambiguity especially when the synonyms belong to the same hierarchy.

For example, the below are two descriptions with an identical text string but the concepts they link to have different meaning:

  • Botulism is the Preferred Term for the concept Intoxication with Clostridium botulinum toxin (disorder).
  • Botulism is an Acceptable synonym for the concept Infection caused by Clostridium botulinum (disorder);

To prevent user confusion through display of look-alike descriptions, search results should always display the Preferred Terms of concepts but allow searching across all synonyms (both Preferred Terms and acceptable synonyms). Refer to the following for further guidance – section 8.1.3 of the SNOMED CT-AU Australian Technical Implementation Guide

Some Preferred Terms or Acceptable synonyms may not reflect typical Australian healthcare use. To modify an existing description or add a new one, please send us a request submission.

Refer to these documents for further details about SNOMED CT descriptions: and

Description id

The description id is the unique identifier for each description type that belongs to a concept. The description id is the primary key for the description file table (in the SNOMED CT-AU RF2 release file format).

For example, the concept id 22298006 has the following seven unique description ids:

  1. Fully Specified Name 751689013 Myocardial infarction (disorder)
  2. Preferred Term 37436014 Myocardial infarction
  3. Acceptable synonym 37442013 Cardiac infarction
  4. Acceptable synonym 37443015 Heart attack
  5. Acceptable synonym 37441018 Infarction of heart
  6. Acceptable synonym 1784872019 MI – myocardial infarction
  7. Acceptable synonym 1784873012 Myocardial infarct

When implementing SNOMED CT-AU data in a system, the description id may be used e.g. as part of obtaining the preferred terms or acceptable synonyms of a concept by linking to the Australian Dialect reference set. However, when recording and storing clinical information within a system, the concept id (not the description id) and its associated description text (usually the Preferred Term) are recommended to be captured. Similarly, during clinical information exchange between systems, the concept id and associated description text is recommended for use.

For further guidance on the description file, refer to

For further guidance on recording and storing clinical information, refer to section 8.2 Recording, storage and display of clinical information of the SNOMED CT-AU Australian Technical Implementation Guide

For further guidance on terminology requirements for clinical information exchange, refer to the NCTS Guidance for Use of Medical Nomenclatures in Information Exchange.

Character length

All descriptions must be displayed fully when used in a system i.e. no truncation. This is to avoid the incorrect selection of a concept for recording in clinical practice.

However, some systems may have character length limits. Some strategies can help assist in this scenario, e.g. creating a tool tip to display the full term or highlighting an incompletely displayed long term.

All descriptions in SNOMED CT have a maximum of 255 characters.

All descriptions in SNOMED CT-AU (including AMT) have a larger maximum of 2048 characters. The larger maximum is mainly to cater for medicinal content (e.g. multi-ingredient preparations with many ingredients, and each ingredient is listed).

As of Jan 2019, only 0.05% of descriptions in SNOMED CT-AU (Australian and international content) that is non-AMT related has greater than 200 characters.

The median length of AMT product descriptions is 47 characters.

How are descriptions authored?

Descriptions are authored or modified by the NCTS terminologists according to the SNOMED CT Editorial Guide (, which contains general criteria and naming conventions, and certain rules and constraints evident from the concept model attributes within different hierarchies.

There are also further editorial guidelines for SNOMED CT-AU, such as the AMT Editorial Rules which have been developed with input from our terminology user community and undergo regular reviews.

Description changes

A change to a description’s text string should always result in a change to its description id. However, depending on the type of change, its related concept id may or may not change.

Minor changes

A concept id may remain unchanged when a description is inactivated and replaced with a new one, for the following minor changes:

  • Capitalisation
  • Punctuation
  • Spelling
  • Word order
  • Moving concept within a single top-level hierarchy

For example, the concept id 175211000036103 remains unchanged and active, while its Preferred Term (description id and associated text string) have been inactivated and replaced.

  • For concept id 175211000036103 |rosuvastatin 10 mg tablet [30] (&) ezetimibe 10 mg tablet [30], 1 pack|, its Preferred Term description id 872731000036117 is inactivated and been replaced by the below description;
  • For the same concept id 175211000036103 |ezetimibe 10 mg tablet [30] (&) rosuvastatin 10 mg tablet [30], 1 pack|, its new Preferred Term description id 1401531000168114 is active, which replaced the above description.

Major changes

For major changes, a concept id must change if the meaning of a concept has changed due to some reason e.g. change in source data, or clinical understanding of that concept. The concept is inactivated (status changed to inactive) and replaced with a newly authored active concept. However, all the descriptions of the original concept remain unchanged, because the descriptions are valid names that still accurately describe the concept.

For example, the original concept 700381000168104 |ADT Booster injection suspension, 0.5 mL syringe| was made inactive and replaced by a new concept 837331000168108 |ADT Booster injection, 0.5 mL syringe| including new FSN and preferred term descriptions.

The original concept’s FSN and preferred term descriptions will however remain active and unchanged in the datafiles.

Read more about SNOMED CT’s inactivation policy and history mechanism from the SNOMED CT Technical Implementation Guide (