SNOMED Clinical Terms -
Introduction
Anne Casey RN, MSc FRCN
Editor Paediatric Nursing
Adviser in Informatics Standards to the Royal College of Nursing
Clinical Domain Lead, NHS (England) Information Standards Board
for Health and Social Care

Overview
Requirements summary
SNOMED CT
– Basics
– Relationships to other terminologies
Getting involved
– IHTSDO governance
– Working groups
‘Local work towards a national / international standard’
Implementation considerations
Discussion

SNOMED CT documents at
www.ihtsdo.org/snomed-ct/snomed-ct-publications/
• SNOMED Clinical terms Fundamentals ppt
• IHTSDO Modeling style guide overview
• SNOMED Clinical Terms® User Guide
• Content inclusion principles and practice
• Style guides: anatomy, clinical findings, procedures etc
• Technical reference guide

eHealth opportunities
– Multi-disciplinary, cross sector records and
communications
– Ways of recording /displaying information not
possible in paper records (helpful record
structures)
– Ways of aggregating individual level data to
support population analyses
– Content standards for clinical elements of
electronic records (that support good standards of
treatment and care)

Context
ICT that supports clinical decision making and the
work of clinicians
Future of cross sector working, team based care,
single shared record, (consumer-owned)
Current ‘mixed economy’ for healthcare records
– separate records for each profession
– single patient record with different sections for each
profession
– single patient record
– Patient/client held record

Content Requirement
patient terminology?
nursing terminology
medical terminology
laboratory terminology
physiotherapy terminology, dietetics, ….
drugs, equipment terminologies
social care terminology
…….

Requirements to support interoperability
in an eHealth world
Standard, multi professional terminology
with characteristics that support data entry, retrieval,
links to decision support, messaging, maps to other
terminologies / classifications, translation etc.

SNOMED Clinical Terms…..
…a terminological resource that can be implemented
in software applications to represent clinically
relevant information
comprehensive (>350,000 concepts)
multi-disciplinary coverage but discipline neutral
structured to support data entry, retrieval, maps etc
Maintained and updated based on user input and
quality review

Requirements drive the design,
development and maintenance of SCT
Requirements related to electronic patient records
– Support for effective delivery of high quality healthcare to individuals and to
populations
General requirements for a terminology
Implementation and migration requirements
Requirements related to the intended user communities
– International, multilingual applicability
– Support for particular local requirements
National and strategic priorities

General Properties
Interface - supporting data entry
– broad coverage, granular, synonyms, pre-coordinated terms,
‘natural language’, translations
Reference - supporting data retrieval
– Subtype hierarchies that allow items to be aggregated
– Defining relationships that allow computation of equivalence
and subsumption
– … and aspects of the terminology that manage context

Relationship between SNOMED CT
and other terminological systems
Different terminologies have features suited to
their different purposes, such as...
clinical definitions
– e.g. pyrexia in an immunocompromised patient = 37.5°C
‘knowledge’ relationships
– e.g. contraindications for use of aspirin
classification concepts
– e.g. other procedure
simple coding scheme for use on paper
grouping / organisation of terms for particular purposes
– e.g. a list of investigations to be done for pyrexial patient

SNOMED CT has a specific set of
purposes – it doesn’t do what some other
‘terminologies’ do..
Example 1. ICF
..describes body functions and structures, activities
and participation - used to understand and measure
health outcomes
Example 2. Nursing terminologies such as NANDA
diagnoses
..support the description of nursing for practice,
education and research; may include knowledge that
supports clinical reasoning (e.g. defining
characteristics of NANDA diagnoses)

Basic Elements of SNOMED CT
Concepts
• The basic units of SNOMED CT
Descriptions
• These relate terms that name the concepts to the concepts
themselves. Each concept has at least two Descriptions.
Relationships
• Relationships are the connections between concepts in SNOMED
CT.
Attributes / qualifiers - properties of concepts
Formal concept definitions - relationships that define the meaning of a
concept relative to other concepts
Tables – SCT distributed as flat files for incorporation into software
(terminology server or direct to EPR ‘catalogue’)

Concepts
Represent distinct clinical meanings
Are identified by a unique numeric identifier (Concept ID)
that never changes and a unique human readable
name (Fully Specified Name)
Are associated with a set of relationships (the “logical
definition”) and two or more descriptions

Descriptions
Concept descriptions relate the terms or names of a SNOMED CT
concept to the concept itself.
“Term” in this context means a phrase used to name a concept. A single
description associates a single term with a single Concept ID.
Descriptions are an important interface property because they give end
users the flexibility to use terms that they are familiar with
The Concept ID ties terms with the same meaning together to aid
consistent interpretation and retrieval.

Description types
Preferred Term
• The most common word or phrase used by
clinicians to name a concept
The Fully Specified Name
• Provides an unambiguous way to name a concept
Synonyms
• The rest of the names that may be used for a
concept

A SNOMED CT Concept
Some of the descriptions associated with ConceptID
22298006:
• Fully Specified Name: Myocardial infarction (disorder)
DescriptionID 751689013
• Preferred term: Myocardial infarction
DescriptionID 37436014
• Synonym: Cardiac infarction
DescriptionID 37442013
• Synonym: Heart attack
DescriptionID 37443015
• Synonym: Infarction of heart
DescriptionID 37441018

FSNs reduce ambiguity
Dressing (oneself) Dressing (observable entity)
parent – personal care
activity
Dressing (e.g. a bandage) Dressing, device (physical
object)
Dressing (assisting the Dressing patient (procedure)
person to dress)
Dressing (of wound) Dressing of wound (procedure)

The problem with words and
meaning
What is a “pyogenic granuloma?”
• Pyogenic = pus forming
• Granuloma = a collection of inflammatory cells
of a particular type
But
• Pyogenic granuloma = a benign tumor of small
blood vessels of the skin
• It is neither pyogenic nor a granuloma.
Combinations are frequently very
different from the sum of their parts

SNOMED is not the “language
police”
SNOMED CT seeks to
• Establish how language is used by clinicians
• To represent meaning as faithfully as possible.
SNOMED CT declares what it thinks a phrase means
• To reflect current usage
• To minimise ambiguity
• Not to shape or control the way a phrase is used
If you want someone to demand that clinicians change what they
call “pyogenic granuloma”
• That may be someone else’s job
• It’s not something SNOMED CT is trying to do

Top-level hierarchies
1. Clinical finding 2. Procedure
3. Observable entity 4. Body structure
5. Organism 6. Substance
7. Pharmaceutical/biologic product 8. Specimen
9. Physical object 10. Physical force
11. Events 12. Environment or geographical
Location
13. Social context 14. Situation with explicit context
15. Staging and scales 16. Qualifier value
17. Special concept 18. Linkage concept
19. Record artifact 20. SNOMED-CT UK Administrative
Concepts

Relationships
The connections between concepts
• Every SNOMED CT concept has at least one
relationship to another concept
• Relationships characterize concepts and give them
their meaning
• The list of relationships for a particular concept makes
up the logical definition of that concept
2 types:
• IS-A (sub-type/super-type)
• Attribute

Relationships cont…
‘Is a’ relationship also known as supertype-subtype or parent
child relationships
A relationship is assigned only when that relationship is
always known to be true (i.e there are no ‘maybes’)

‘Only necessarily true’
‘Pain in calf’ is included in SNOMED CT as it is a
concept agreed to be relevant in practice
It is also possible to say which calf, how severe,
how long etc but these are NOT definitional of
the specific phrase ‘pain in calf’

Attribute Relationships
Characterize and specify concepts
An example of an attribute is FINDING-SITE,
which is used to further specify Disease
concepts
- e.g. part of the logical definition of the concept
Pneumonia in SNOMED CT is:
- Concept = Pneumonia
- Attribute = FINDING-SITE
- Value of attribute = Lung structure

‘Context’
Context refers to the effects of embedding a concept
code in a clinical statement
A code is embedded in a clinical statement when it is used in a
clinical record
Embedding a code in a clinical statement
Adds information
– Date of finding or action
– Author, performer, etc.
May also elaborate its meaning in one of several ways
– Subtype qualification
– Axis modification
– Affirmation or Negation
– Combination

Context: Representation
Context can be represented in various ways
Pre-coordination of SNOMED CT concepts
– Example
160303001 Family History of diabetes mellitus
Post-coordination of SNOMED CT concepts that together express a
more specific concept
– Example
57177007+(246090004=73211009 ) Family history + (Assoc. finding = Diabetes
mellitus)
Structures and attributes specific to a proprietary data model or a
standard reference model
– Examples from HL7 RIM
ActRelationshipclass
moodCodeattribute

Other things –
RefSets: Reference Sets [aka Subsets] including language
RefSets
Extensions: support Realm-specific content that is not required
in the international release
e.g.leave granted under the Mental Health Act 1983 (England and
Wales)
Cross Maps: linking SNOMED CT to other terminologies
mechanisms for developing and maintaining
shared resources

Reference Set mechanism
‘The effective usage of SNOMED CT requires a way to
refer to sets of components that are appropriate for a
specific use case’
This ‘referring to’ is achieved by the SNOMED CT
Reference Set mechanism
[SNOMED CT Reference Sets at www.ihtsdo.org]
NOTE: The preferred term is Reference Set (RefSet),
as Subset is potentially misleading (and the RefSet
mechanism does more than the original SNOMED
Subset mechanism).

Terminology Infrastructure
IHTSDO Board
SNOMED CT
Committees
international feedback
Working groups
SNOMED CT
National terminology Service + national subsets
National working groups & extensions
System suppliers
SNOMED CT
In Use
Other Terminologies

Nursing Special Interest Group
Reports to IHTSDO Content Committee
Objectives:
– ensure adequate content to support nursing practice
– Identify and prioritize new content inclusion
– Develop partnerships and relationships with (nursing) system suppliers
& other specialty organization
– Provide guidance about the use of SNOMED CT in Nursing practice
Open membership: ICN, ANA, RCN, nurses from IT, clinical
practice, education

Examples of Nursing SIG projects
Working with SNOMED CT – basic guide
Education, advice and counselling
Representing assessment scales in
SNOMED CT
Lines, catheters, cannulae – with anaesthesia

Education Special Interest Group
Reports to Quality Committee
Open participation
Issues
– conflict of interest declaration
– IPR issues
– volunteer v funded work
– Consensus v evidence based
– use what’s out there; provide back to others;
evaluate and refine

Education SIG priorities
SNOMED Editors’ curriculum
– Specialist additions: mappers, translators
– Competency framework and certification
– Informs tools specification (safe place to practise!)
SNOMED Implementers’ curriculum
[educational needs of clinical and other communities]
NB curriculum v syllabus or standard course content

SNOMED CT Content development
Expert
committee
System content SNOMED CT
developer
End user

Contributions to content
development and quality review
Specialty lists - making implementation easier:
radiology, general practice, nursing
Encoding of national (international?) standards
– Assessment instruments: Glasgow coma scale, Barthel
index,
– Standard structured records / clinical datasets: diabetic
retinopathy screening record, national renal dataset
– Archetype repositories

Wouldn’t it be
good if..
Clinical guidelines and
accompanying audit
datasets used consistent,
SNOMED aligned
terminology

Local work…
Emergency Department diagnosis recording using SNOMED ED
Subset v national data dictionary term list
450 terms v 22 terms (including diagnosis not classifiable)
PRE: 28.9% of 18,457 records had no recorded diagnosis.
POST: 7.7% of 18,798 records had no recorded diagnosis
Lessons learnt: gaps in subset (770); anatomy post co-ordinated?
Tony Shannon, Consultant in Emergency Medicine, Leeds Teaching Hospital &
Clinical Lead, Clinical Content Service, NHS Connecting for Health

SNOMED CT –
a terminological resource
‘The benefit of recording information in a
standard terminology such as SNOMED CT is
linked to the benefits of the electronic care
record and the benefits of recording clinical
information in a structured form’
SNOMED CT - the language of the NHS Care Records Service.
www.connectingforhealth.nhs.uk/publications

Content standards
A ‘terminological resource’
= Many ways to say the
same thing
SNOMED CT
366,000 Coded Concepts
993,000 Terms For patient safety and
1.46M Relationships good communication we
need standards for record
and message content
including restricted sets of
SNOMED terms/codes

Implementation requires evolution of….
SNOMED CT – usable components work
Systems
Users
In the context of ACTUAL
requirements for coded
data (also evolving)

Implementation of SNOMED CT
in clinical systems
‘Level 2 systems have internal support for SNOMED CT
using both pre and post co-ordinated content…..
most fully exploit the benefits of using SCT.
For the most part these systems do not exist and will
require the development of new user interfaces,
database information and system interfaces.’
[Implementing SNOMED CT within national electronic record solutions –
CHIRAD Health Informatics, www.chirad.org.uk – Big Issue]

Users?
1. Clinicians
Administrative and secretarial staff
Secondary users of data: researchers,
auditors, coders ..
2. System content developers including
expert clinicians
3. Terminology developers

Migration of clinician users…
…from unstructured, non …to structured, standard
standard, narrative records records and messages
…from vague, ambiguous, ...to standard, defined,
local terminology and locally evidence based
adapted clinical tools terminologies and tools
...from paper records …to ICT that supports
clinical workflow, decision
making, recording and
communication (and has
standard terminology for
interoperability)