1. Lecture 12: Terminologies and Classification
Systems
Dr. Martin Chapman
Principles of Health Informatics (7MPE1000). https://martinchapman.co.uk/teaching

2. Lecture structure
This will mostly be a practical lecture, giving you the opportunity to
independently gain an understanding of different clinical
terminologies.
We will use online software to look at ICD-10 codes, Read codes and
SNOMED CT codes.
Look out for URLs throughout the lecture and use a laptop or other
mobile device to access each platform.

3. Lecture limitations
Coding systems are detailed and constantly evolving.
Similarly, the pieces of browsing software used to present different
coding systems are detailed and constantly evolving.
As such, there may be features – of both the terminologies and
browsing software – that aren’t covered here or, indeed, that I do not
know about.
Let’s learn together!

4. Learning outcomes
1. Be able to understand the key characteristics of three different
(clinical) terminologies.

5. International Classification of Diseases
(ICD)
Tenth revision (ICD-10)

6. https://icd.who.int/browse10/2019/en

7. Questions
1. Which (clinical) domain is covered by this terminology?
2. How are the terms in the terminology structured?
1. What range of codes are available?
2. Is there a relationship between the codes?
3. Are there any provisions made for mapping to other
terminologies?
4. Are there any obvious limitations to the terminology?
https://icd.who.int/browse10/2019/en

8. Which (clinical) domain is covered by this
terminology?
Covers disease and other health problems.
Allows morbidity (suffering from a disease) and mortality (death)
information from around the world to be systematically recorded.

9. How are the terms in the terminology structured?
In their simplest form, ICD-10 codes are three alphanumeric
characters from A00 to Z99.
‘U’ codes are used for
emerging diseases like COVID
(at the time), as we have seen.

10. How are the terms in the terminology structured?
When required, a fourth character can be added to create sub-
categories:
We may also see examples of
a fifth character being added,
to create additional categories.
This creates a form
of hierarchy.

11. How are the terms in the terminology structured?
Chapters
Separation into blocks
depends upon what the
focus of the current
chapter is (multi-axial).
Here, for example, the
focus is disease, so
each block represents
different modes of
transmission
The relationship
between codes, blocks
and chapters forms an
additional hierarchy.

12. Are there any provisions made for mapping to other
terminologies?
No immediate evidence of mapping (at least not on this browser).
This may be because ICD-10 is considered the single standard for
recording disease prevalence around the world, and thus other
terminologies map to it.

13. Are there any obvious limitations to the terminology?
Many adjustments have been made to try
and cover a broad range of areas (beyond
morbidity and mortality), resulting in a
terminology that perhaps tries to cover too
much, and its remit becomes confusing as a
result.
May not be as useful in a clinical setting.
(Remember we were broadly referring to these terminologies as
‘clinical’, but, in fact, terminologies do have a wider remit).
Note: ICD-10-CM, an extension, does have codes for diagnoses
and procedures.

14. Aside: The wider ICD family

15. Read Codes
‘Clinical Terms’

16. https://bioportal.bioontology.org/ontologies/RCD/?p=summary
Note: Because Read Codes are
retired, we do not have a direct
browser, but viewing the
terminology as an ontology
should still be useful.

17. Questions
1. Which (clinical) domain is covered by this terminology?
2. How are the terms in the ontology structured?
1. What range of codes are available?
2. Is there a relationship between the codes?
3. Are there any provisions made for mapping to other
terminologies?
4. Are there any obvious limitations to the terminology?
For all these questions, how does the current terminology differ from those seen
previously?
https://bioportal.bioontology.org/ontologies/RCD/?p=summary

18. Which (clinical) domain is covered by this
terminology?
Predominantly designed for general clinical use, in order to code
events in the EHR. This contrasts the (broader) focus on disease
taken by ICD-10.
Like ICD-10, we again
encounter a hierarchical
structure that allows us to
explore logically.
We can already see more terms
that would be relevant to a
clinical setting.

19. How are the terms in the terminology structured?
Unlike ICD-10, hierarchy
is not built into the codes
themselves (e.g. A00 vs
A00.1), nor is there a
finite range of codes, but
there are links between
the terms, across which
properties can be
inherited.
Type Unique Identifier. This is inherited
between terms that connect to each other.
Concept Unique Identifier

20. How are the terms in the terminology structured?
Later versions of the Read codes terminology have a
compositional aspect that involves combining terms with
qualifiers (that can have a certain value) to create new terms.
An entity called a template (rather than a ontology) controls
combinations.
Term Qualifier Qualifier value
Hand fixation of fracture
using intramedullary nail

21. Are there any provisions made for mapping to other
terminologies?
Lots! Particularly to ICD-10.
Read codes in particular focus on the integrity of mappings, by
having a set of quality insurance rules that check structure.

22. Are there any obvious limitations to the terminology?
Read codes were revised multiple times before ultimately being retired
because of many of the limitations of models we’ve seen, including
being a snapshot that becomes less useful over time.
There were other limitations to Read codes, including the inability of
the templates we’ve seen to properly control the composition process.

23. SNOMED CT

24. https://termbrowser.nhs.uk/?perspective=full&edition=uk-
edition&release=v20230215&server=https://termbrowser.n
hs.uk/sct-browser-api/snomed

25. Questions
1. Which (clinical) domain is covered by this terminology?
2. How are the terms in the ontology structured?
1. What range of codes are available?
2. Is there a relationship between the codes?
3. Are there any provisions made for mapping to other
terminologies?
4. Are there any obvious limitations to the terminology?
For all these questions, how does the current terminology differ from those seen
previously?
https://termbrowser.nhs.uk/?perspective=full&edition=uk-
edition&release=v20230215&server=https://termbrowser.nh
s.uk/sct-browser-api/snomed

26. Which (clinical) domain is covered by this terminology?
Much like Read codes, SNOMED CT aims to provide a means to
code a broad range of clinical events in the EHR. Indeed, as
discussed, its use now supersedes the use of Read codes.
Like ICD-10 and Read, we
again encounter a hierarchical
structure that allows us to
explore logically.
We can again see terms that
would be relevant to a clinical
setting.
SNOMED CT is cited as
having a >90% coverage of
common patient problems.

27. How are the terms in the terminology structured?
Similar to Read codes, we
once again have connections
between our concepts creating
a hierarchy (parents and
children).
This is also the first time we
see connected terms, concepts
and codes (Lecture 11) in
practice.

28. How are the terms in the terminology structured?
We also see a more explicit
example of multi-axial
classification (the block separation
in ICD-10 was less overt).

29. Are there any provisions made for mapping to other
terminologies?
We again see a focus on mapping to ICD-10.

30. SNOMED CT is large (~300,000 concepts), meaning
that some redundancy is inevitable.
Such a large number of terms can also result in errors,
such as ambiguous terms, terms with illogical hierarchies,
or terms that perhaps do not fall within the scope of the
terminology.
Are there any obvious limitations to the terminology?

31. Summary
ICD-10, Read codes and SNOMED CT are three examples of
(clinical) terminologies.
ICD-10 is primarily designed to focus on disease, but does have
clinical extensions. Read and SNOMED CT aim to directly cover a
broad range of clinical problems.
All three terminologies employ some hierarchical structure to
organise their terms, with SNOMED CT utilising multi-axial
connections most explicitly.
Both Read and SNOMED CT map to ICD 10.
Trying to be too broad is a common source of issues with clinical
terminologies.

32. References and Images
Enrico Coiera. Guide to Health Informatics (3rd ed.). CRC Press, 2015.