A brief introduction to SNOMED CT - the ontology based medical terminology. This covers the basic definitions, the difference between SNOMED CT and ICD9, Post co-ordination use-cases and some general information. This is not an extensive guide for SNOMED CT adoption in a system

1. Introduction to SNOMED
Guru Kini

2. Overview
What is SNOMED
Applications of SNOMED
Concepts, Hierarchies & Relationships
SNOMED vs. ICD9
Post Co-ordination and Pre Co-ordination
Things to consider before opting for SNOMED
This may be useful for requirement analysts, project managers or software developers
who are faced with implementing SNOMED support in the healthcare related software.
This is not a How-To guide or a detailed technical analysis of SNOMED. However, there
are several useful references in the notes and the slides for these contexts.
Apologies for the heavily bulleted slides

3. What is SNOMED?
Systemized NOmenclature of MEDicine
It is an organized lists of a wide variety of clinical terminology
defined with unique codes
Perhaps the most comprehensive clinical terminology in the
world
It is older than you think!
Started as early as 1965
Has had several iterations since
Currently used variant: SNOMED Clinical Terms (SNOMED CT)
Provides cross maps to various terminologies such as ICD9,
ICD10 and LOINC
Continued…

4. What is SNOMED? (contd.)
SNOMED covers a wide no. of medical terminologies for
Disorders and finding (what was observed)
Procedures (what was done)
Event (what happened)
Substance/Medication (what was consumed/administered)
Pretty much anything that may be used to capture Medical
data
SNOMED is designed as an Ontology
Each Concept could have relationships with other Concepts

5. What is an ontology?
Ontology is a formalized model for particular domain
Consists of 4 basic elements:
Individuals/Objects – an actual, concrete instance of
something that can described as a part of the ontology (viz.,
Angina, Class 1)
Classes – abstract concepts (Procedure, Disease, etc.).
Essentially a “category” for a set of Individuals
Attributes – certain properties associated with a class
Relations – define who certain classes (and objects) are
related to each other
Yes, a class diagram of a program written in an OO
programming language is a visual representation of an
ontology

6. Where can I find SNOMED codes?
National Library of Medicine’s UMLS is the one stop
shop for SNOMED codes
SNOMED is now freely available for use for U.S. users
It is now maintained by International Health
Terminology Standards Development Organization
(IHTSDO)

7. Concepts, Hierarchies &
Relationships
A “Concept” is the basic unit in SNOMED
Has a numeric representation (Concept ID), which is assigned arbitrarily
Can represent anything that may have a possible use in recording clinical
information
The same Concept could have several “Synonyms” to accommodate
variations in name. E.g., “Myocardial infarction” could also be called
“Infarction of heart” or just “Heart Attack”
All Concepts are divided in “Hierarchies”
Hierarchies do not overlap
Clinical Finding/Disorder, Procedure, Substance, etc. are all examples
There are some 20+ main hierarchies, more can be added over time
“Relationships” between Concepts can be defined
“Is a” is most common relationship
Other relationships could be defined as “Attributes” of a Concept

8. Example: using SNOMED
relationships
Disease
Is a type of
Disorder of body site
Is a type of
Legend
Disorder
Synonym
Body
Structure
Disorder of body
system
Is a type of
Is a type of
Disorder of
endocrine system
Disorder of foetus or
newborn
Is a type of
Is a type of
Relation
Diabetes mellitus
Is a type of
Endocrine pancreatic
structure
Found in
Neonatal disorder
Is a type of
Neonatal diabetes
mellitus
AKA
Diabetes mellitus
syndrome in
newborn infant

9. Top SNOMED Hierarchies
80000
70000
60000
50000
40000
74758
30000
50060
20000
41221
27623
10000
26210
23700
0
Disorder
Procedure
Finding
Organism
Body
Substance
Structure

10. Disorder vs. Finding
• Disorders and findings often used interchangeably
• “Finding” is a general observation or a judgment of the patient’s
physical, mental or social condition (current or historical). A finding need
not be an “abnormal” state and can be somewhat vague. E.g.:
• Patient complaints/Symptoms (e.g., cough, shivering)
• Lab result observations (e.g., Allergy Skin Test Positive)
• Social setting (e.g., Unsafe play area, Patient’s dependents)
• A “Disorder” or “Disease” is a sub-set of “Finding” concept that are
necessarily abnormal physical or mental conditions for the patient. E.g.:
• Tuberculosis
• Angina, Class I
• A Finding may be the initial diagnosis of the patient’s condition which
may lead to the discovery of a Disorder. E.g.,
• A complaint of Chest pain (Finding) may lead to a final diagnosis of
Angina, Class I (Disorder)
• Bleeding of Gums (Finding) may lead to Hematoma of gingivae (Disorder)
• Cough (Finding) may lead to Tuberculosis (Disorder)

11. SNOMED vs. ICD
ICD is a relatively ancient code family
Late 19th century roots
ICD9 was developed in 1970s! Even ICD10 is ~30 years old!
ICD is a classification whereas SNOMED is a terminology
ICD tends to be more abstract. With SNOMED the user can get a
more accurate description
ICD9 (or ICD10) tend to have a “unspecified” catch-all slot for
most disorders.
SNOMED is far more extensive than ICD9
ICD only covers disorders
SNOMED is implemented as an ontology
Any number of relationships can be defined for each concept
Continued…

12. SNOMED vs. ICD (contd.)
SNOMED CT – is better suited for capturing relevant data during an
encounter
Allows the user to capture the various aspects associated with a disorder (Post
Coordination)
This encourages the user to capture associated information like Severity, Body
part affected, Cause (force or substance), laterality (viz., left or right), Morphology
(form) in structured form
ICD9/10 – used in cases where data need not be very granular
Each code is very rigidly defined and does not support qualifiers
Used in Insurance billing, Morbidity recording (death cause etc.), Epidemiological
tracking (public health surveillance)
These use-cases usually can work with a general disease class
Usually, SNOMED CT is considered a good way to enter the medical
information and ICD9/10 is considered a good way to export information

13. SNOMED CT to ICD9/10 Conversions
Why convert?
Business requirements - e.g., your Billing Clearing house may insist on
ICD9/ICD10
Interoperability – to import CCD/CCR from other sources that use
ICD9/ICD10
Future-proofing – ICD10 may eventually be the de facto standard
SNOMED CT provides cross-mapping with ICD9 and ICD10
terminologies
Since SNOMED CT is much larger in size and because ICD9/10
primarily deal with disorders, only a portion of SNOMEC can be
mapped.
ICD9/ICD10 to SNOMED is mostly 1:1, however SNOMED to
ICD9/ICD10 may have a number of 1:Many mapping
May need user input or context based intelligence to convert

14. Post Coordination
Post Co-ordination: representing a medical term using two or
more SNOMED concepts. E.g., “Wound in the right hand” could
be coded in parts
Wound (Disorder)
399963005
Found in
Hand (Body
Structure)
302539009
Laterality
Right (Qualifier)
24028007
SNOMED’s ontological structure naturally lends itself to Post Coordination based capturing of data.
However, it can cause confusion as the same concept can be
represented in more than one way! E.g.
Wound in hand
(Disorder)
283059006
Laterality
Right (Qualifier)
24028007
Continued…

15. Post Coordination (contd.)
ICD9/10 is design to be Pre Co-ordination oriented. That
is, there is usually one unique code for a given medical
term.
It also implies that one cannot capture much of term’s
associative data using ICD9/10 itself
Some of the SNOMED “leaf” concepts are specific enough
to be used as Pre Co-ordinated terms
For any system, Pre- vs Post- arguments essentially deal
with one question: “For capturing a medical term, what do
you need more: uniqueness or granularity”?

16. Things to consider before implementing
SNOMED CT in your system
Familiarize yourself
Use a SNOMED CT Browser
Look at some existing SNOMED subsets (CORE, VA/KP)
Consider your use-cases
Determine which hierarchies will the system use
(Finding, Procedure, Disorder)
Determine which concepts will the system use (Create a Subset)
Determine when will your system use primitive (generic/vague) and nonprimitive (specific) concepts
Consider your conversion requirements
Look at the UMLS Metathesaurus and see if you can use that instead of
SNOMED
Allow room for updates
SNOMED CT releases updates twice a year
Your system should be able to accept the updates without going out-ofaction

17. References
http://protege.stanford.edu/publications/ontology_de
velopment/ontology101-noy-mcguinness.html - What
is an Ontology
http://perspectives.ahima.org/a-comparison-betweena-snomed-ct-problem-list-and-the-icd-10-cmpcs-hipaacode-sets/ - Comparing ICD10 and SNOMED CT
http://www.connectingforhealth.nhs.uk/elearning/sn
omedct/flash/ - SNOMED Intro by NHS