Introduction

In January 2017, the Content Managers Advisory Group (CMAG) initiated an action to conduct a survey of the national extensions that were available, to date there has been limited information available - to other members and presumably SNOMED International. The responses of this survey are available here. The results shows a variety of extensions are produced, ranging from subset/refset, language translations and clinical content development. Subsequent activities investigating collaboration on subset may be pursued, but the CMAG was also interested in exactly what clinical content was in each extension, and how this might be shared. There should be very little clinical content that is exclusive to any country, and if it has been developed by one extension - it's likely globally relevant, and sharing it can reduce duplicated effort and maintenance burden of extension builders.

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A summary of the results is available in the conclusion section at the end of this paper.

The cooperation of all Members is appreciated, and whilst all effort has been made to represent the extensions accurately, any inaccuracies are accidental.

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14 NRC responded to the survey, with 9 indicating they created clinical content extensions.
The Australian Edition also includes it's national drug extension, which has been excluded from this round of analysis (as no other extension appeared to include such content)
All extensions were based upon the July 2016 international release except one. This exception may produce some anomalies, but they are limited to the extension. 

A raw analysis of the active concepts within an extension.

Ratio of active to inactive concepts

All analysis was only performed on active content.

Extension changes against International Concept IDs

A total of 40 core concepts have been modified by extensions in some way.
Two were retired by an extension

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select id,count(*) from X_Concepts
where id in (246089008,246221002,260670006,263512003,263513008,447564002,449609005,700043003,11000119105,41000179103,441000119109,601000119109,1111000119100,1561000119105,4181000179103,4191000179101,4201000179104,4211000179102,4221000179107,4231000179109,4241000179101,4251000179103,4261000179100,4271000179106,4281000179108,4301000179109,4311000179106,4321000179101,4331000179104,4341000179107,4351000179105,5461000179100,5471000179106,5481000179108,5491000179105,5531000179105)
and moduleId != 161771000036108 
group by id
having count(distinct moduleId) > 1

Extension Concepts

There appears to be around 52 unique semantic tags across the extension content. many of these are attributable to translations. Not all extensions provide english FSNs for extension content^{Results of Analysis of SNOMED CT Extensions (2017)1}, semantic tags were manually translated and merged.
After normalisation, this comes to 32 semantic tags. The distribution of content is shown below.

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The type of content by hierarchy

Each Top level hierarchy reviewed below for extension content.
Duplicates were found by comparing terms across extensions within given hierarchy. For example, "Look for duplicate terms within the procedure hierarchy". Duplicates within a module were also ignored.

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SET @Hierarchy = 404684003;

select term,count(distinct moduleId) from X_Descriptions
where conceptId in (select distinct id from X_Concepts where active)
and moduleId != 900062011000036108 -- exclude AMT module
-- and moduleId not in(900000000000207008,900000000000012004) -- exclude international
and typeId = 900000000000003001
and conceptId in (select sourceId from X_TransitiveClosure where destinationId = @Hierarchy)
and active = 1
group by term
having count(distinct moduleId) > 1;

-- candidates for consideration.
select * from X_Descriptions
-- active descriptions for active concepts
where active and conceptId in (select distinct id from X_Concepts where active)
-- target hierarchy
and conceptId in (select sourceId from X_TransitiveClosure where destinationId = @Hierarchy)
and term in (select distinct term from X_Descriptions
					where conceptId in (select distinct id from X_Concepts where active)
					and moduleId != 900062011000036108 -- exclude AMT module
					-- and moduleId not in(900000000000207008,900000000000012004)
					and conceptId in (select sourceId from X_TransitiveClosure where destinationId = @Hierarchy)
					and active = 1
					group by term
					having count(distinct moduleId) > 1);

Clinical finding

NRC,Concepts
SNOMED CT Netherlands NRC maintained ,681
US National Library of Medicine maintained ,3461
Uruguay extension module,14
Canada Health Infoway English ,73
SNOMED CT Sweden NRC maintained ,548
Danish ,24
SNOMED Clinical Terms Australian extension,74
SNOMED CT United Kingdom clinical extension ,8586

Potential Concept Duplication

26 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These may have different character encoding or punctuation conventions, or written languages are genuinely similar (Danish and Swedish). A binary (eliminating case differences) compare halved the number of duplicate terms identified. It's unclear (to the author) what the standards and rules are concerning translations - are they complete (all concepts), some (only concepts of interest), as necessary (where word is different).

Procedure

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,43
US National Library of Medicine maintained ,751
Uruguay extension module,176
Canada Health Infoway English ,1214
SNOMED CT Sweden NRC maintained ,483
Danish ,1
SNOMED Clinical Terms Australian extension,960
SNOMED CT United Kingdom clinical extension ,9732

Potential Concept Duplication

16 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

Admission to nursing home (procedure)
Alpha-1 microglobulin measurement (procedure)
Autopsy planned (situation)
"Computed tomography of head, neck, abdomen and pelvis with contrast (procedure)"
Decompressive craniectomy (procedure)
electrochemotherapy (procedure)
Flexible ureteroscopy (procedure)
Injection of platelet-rich plasma (procedure)
Laparoscopic extended right hemicolectomy (procedure)
Laparoscopic gastrectomy (procedure)
Laparoscopic radical prostatectomy (procedure)
Open reduction of fracture of ankle with internal fixation (procedure)
Open repair of strangulated incisional hernia (procedure)
Open repair of strangulated incisional hernia with prosthesis (procedure)
Rigid ureteroscopy (procedure)
Smoking assessment (procedure)

Special concept

NRC,Concepts
SNOMED CT Netherlands NRC maintained ,370
US National Library of Medicine maintained ,1823
Uruguay extension module,59
Canada Health Infoway English ,374
SNOMED CT Sweden NRC maintained ,254
Danish ,53
SNOMED Clinical Terms Australian extension,308
SNOMED CT United Kingdom clinical extension ,4379

Potential Concept Duplication

15 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

5-Hydroxyhistamine (substance)
Atypical atrial flutter (disorder)
Autopsy planned (situation)
Birch pollen (substance)
Decompressive craniectomy (procedure)
Deer dander (substance)
Escherichia coli serogroup Orough (organism)
Highlands j virus (organism)
No diabetic retinopathy (situation)
Subendocardial myocardial infarction (disorder)
Suspected cerebrovascular accident (situation)
Suspected sepsis (situation)
Takotsubo cardiomyopathy (disorder)
Thrombosis of internal jugular vein (disorder)
Typical atrial flutter (disorder)

Situation with explicit context

NRC,Concepts
SNOMED CT Netherlands NRC maintained ,71
US National Library of Medicine maintained ,340
Uruguay extension module,52
Canada Health Infoway English ,376
SNOMED CT Sweden NRC maintained ,194
SNOMED Clinical Terms Australian extension,114
SNOMED CT United Kingdom clinical extension ,2877

Potential Concept Duplication

8 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

Autopsy planned (situation)
Family history of lactose intolerance (situation)
History of acute coronary syndrome (situation)
History of amaurosis fugax (situation)
History of supraventricular tachycardia (situation)
No diabetic retinopathy (situation)
Suspected cerebrovascular accident (situation)
Suspected sepsis (situation)

Observable entity

NRC,Concepts
SNOMED CT Netherlands NRC maintained ,20
US National Library of Medicine maintained ,28
Uruguay extension module,26
Canada Health Infoway English ,3
SNOMED CT Sweden NRC maintained ,62
Danish ,11
SNOMED Clinical Terms Australian extension,4
SNOMED CT United Kingdom clinical extension ,5538

Potential Concept Duplication

There are no FSNs duplicated across the content.
There are 476 duplicate synonyms across this set. The affected concepts are in the following extensions.

• SNOMED CT Netherlands NRC maintained module
• SNOMED CT core module
• Danish module
• SNOMED CT Sweden NRC maintained module
• SNOMED CT United Kingdom clinical extension module

Event

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,2
US National Library of Medicine maintained ,15
Uruguay extension module,1
Danish ,1
SNOMED CT United Kingdom clinical extension ,2230

Potential Concept Duplication

No FSNs are duplicated across the content.
17 synonyms are duplicated, the affected concepts are in the following extensions.

• Danish module
• SNOMED CT core module
• SNOMED CT Sweden NRC maintained module
• SNOMED CT Netherlands NRC maintained module

Qualifier value

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,100
US National Library of Medicine maintained ,217
Uruguay extension module,104
Canada Health Infoway English ,396
SNOMED CT Sweden NRC maintained ,4
Danish ,132
SNOMED Clinical Terms Australian extension,86
SNOMED CT United Kingdom clinical extension ,2001

Potential Concept Duplication

28 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

Adolescent medicine service (qualifier value),Adolescent psychiatry service (qualifier value)
Audiometry (qualifier value),Cardiology service (qualifier value)
Chiropody (qualifier value),Clinical allergy service (qualifier value)
Clinical genetics service (qualifier value),Clinical immunology service (qualifier value)
Clinical neurophysiology service (qualifier value),Dental hygiene service (qualifier value)
Dentistry service (qualifier value),Dialysis service (qualifier value)
Endodontic service (qualifier value),Genetics (qualifier value)
Health belief model (qualifier value),Infectious diseases service (qualifier value)
Intensive care medicine (qualifier value),Neonatal intensive care service (qualifier value)
Nephrology service (qualifier value),Neurology service (qualifier value)
Physiotherapy service (qualifier value),Prosthetics (qualifier value)
Prosthetics service (qualifier value),Prosthodontic service (qualifier value)
Psychology (qualifier value),Respiratory medicine service (qualifier value)
Respite care service (qualifier value),Sports medicine (qualifier value)

Record artifact

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,202
US National Library of Medicine maintained ,4
Uruguay extension module,57
SNOMED CT Sweden NRC maintained ,1
SNOMED CT United Kingdom clinical extension ,1078

Potential Concept Duplication

8 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

 Discharge letter (record artifact)
Do not attempt cardiopulmonary resuscitation order (record artifact)
Growth chart (record artifact)
Letter (record artifact)
Living will and advance directive record (record artifact)
Medical photograph (record artifact)
Referral letter (record artifact)
Weight chart (record artifact)

Social context

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,5
US National Library of Medicine maintained ,41
Uruguay extension module,56
Canada Health Infoway English ,56
SNOMED CT Sweden NRC maintained ,3
Danish ,21
SNOMED Clinical Terms Australian extension,6
SNOMED CT United Kingdom clinical extension ,603

Potential Concept Duplication

5 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

 Massage therapist (occupation)
Maternal aunt (person)
Maternal uncle (person)
Paternal aunt (person)
Paternal uncle (person)

Substance

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,4
US National Library of Medicine maintained ,418
Canada Health Infoway English ,292
SNOMED CT Sweden NRC maintained ,3
Danish ,166
SNOMED Clinical Terms Australian extension,60
SNOMED CT United Kingdom clinical extension ,20

Potential Concept Duplication

15 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

 5-Hydroxyhistamine (substance)
Arugula (substance)
Birch pollen (substance)
Blue cheese (substance)
Deer dander (substance)
Flounder (substance)
Ham (substance)
Hickory nut (substance)
Honeydew melon (substance)
Jalapeno pepper (substance)
Pneumococcal conjugate vaccine (product)
Red onion (substance)
Snail - dietary (substance)
Tree nut (substance)
White pepper (substance)

Body structure

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,1
US National Library of Medicine maintained ,21
Uruguay extension module,1
Canada Health Infoway English ,4
SNOMED CT Sweden NRC maintained ,2
Danish ,4
SNOMED Clinical Terms Australian extension,2
SNOMED CT United Kingdom clinical extension ,393

Potential Concept Duplication

No FSNs duplicated across the content.

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• Danish module
• SNOMED CT Sweden NRC maintained module
• SNOMED CT core module
• Lithuania
• SNOMED Clinical Terms Australian extension
• US National Library of Medicine maintained module
• SNOMED CT United Kingdom clinical extension module

Staging and scales

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,1
US National Library of Medicine maintained ,5
SNOMED CT Sweden NRC maintained ,12
Danish ,1
SNOMED Clinical Terms Australian extension,2
SNOMED CT United Kingdom clinical extension ,535

Potential Concept Duplication

No FSNs duplicated across the content, which are almost certainly candidates for promotion.
464 synonyms are duplicated across the extensions. The affected concepts are in the following extensions.

• Danish module
• SNOMED CT core module
• SNOMED CT Sweden NRC maintained module
• SNOMED CT United Kingdom clinical extension module

Pharmaceutical / biologic product

 NRC,Concepts
US National Library of Medicine maintained ,263
Canada Health Infoway English ,240
Danish ,141
SNOMED Clinical Terms Australian extension,30
SNOMED CT United Kingdom clinical extension ,47

Potential Concept Duplication

12 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

 Arugula (substance)
Blue cheese (substance)
Flounder (substance)
Ham (substance)
Hickory nut (substance)
Honeydew melon (substance)
Jalapeno pepper (substance)
Pneumococcal conjugate vaccine (product)
Red onion (substance)
Snail - dietary (substance)
Tree nut (substance)
White pepper (substance)

Organism

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,73
US National Library of Medicine maintained ,24
SNOMED CT Sweden NRC maintained ,1
Danish ,12
SNOMED Clinical Terms Australian extension,1
SNOMED CT United Kingdom clinical extension ,3

Potential Concept Duplication

2 FSNs duplicated across the content, which are almost certainly candidates for promotion.
The affected concepts are in the following extensions.

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These are the identified FSNs.

Escherichia coli serogroup Orough (organism)
Highlands j virus (organism)

Environment or geographical location

NRC,Concepts
US National Library of Medicine maintained ,11
Canada Health Infoway English ,4
Danish ,41
SNOMED CT United Kingdom clinical extension ,81

Potential Concept Duplication

No FSNs duplicated across the content.
353 synonyms are duplicated across the extensions, The affected concepts are in the following extensions.

• Danish module
• SNOMED CT Sweden NRC maintained module
• SNOMED CT core module
• Lithuania

Specimen

 NRC,Concepts
US National Library of Medicine maintained ,38
SNOMED CT United Kingdom clinical extension ,56

Potential Concept Duplication

No FSNs duplicated across the content.
Nine synonyms are duplicated. The affected concepts are in the following extensions.

• Danish module
• SNOMED CT Sweden NRC maintained module
• SNOMED CT core module
• US National Library of Medicine maintained module
• SNOMED CT United Kingdom clinical extension module

Physical object

 NRC,Concepts
SNOMED CT Netherlands NRC maintained ,5
US National Library of Medicine maintained ,33
SNOMED CT Sweden NRC maintained ,1
SNOMED CT United Kingdom clinical extension ,20

Potential Concept Duplication

No FSNs duplicated across the conten.
399 synonyms are duplicated across the extensions. The affected concepts are in the following extensions.

• Danish module
• SNOMED CT Sweden NRC maintained module
• SNOMED CT core module

Physical force

Single Concept : U-V radiation in diagnosis NOS (physical force)
 

Extension Descriptions

Most analysis performed as part of identifying duplicates within concepts. However, below is a summary of the translations - (extension descriptions for core concepts).

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Language,Concepts
da,254752
en,6327
es,227
fr,34063
lt,42668
nl,6756
sv,298331

Extension Changes to Core Descriptions

178 International descriptions have some modification in an extension. The associated modules are:

• Australian common model component extension
• SNOMED Clinical Terms Australian extension
• US National Library of Medicine maintained module

Relationship Extensions

5,136 core concepts have been changes within an extension. Some of these look like promotions, however the majority do not appear to be.
 

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Note: Some of the numbers comparing stated and inferred look odd, this is likely a result of the crude aggregation of extensions and some of the extension content already having been promoted to core.

Core relationships modified within an Extension

1,997 core relationships where modified by an extension, affecting 384 concepts

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NRC,Relationships Changed
SNOMED CT Netherlands NRC maintained module,1570
Uruguay extension module,296
Canada Health Infoway English module,80
SNOMED CT Sweden NRC maintained module,16
Australian common model component extension,12
Danish module,8
SNOMED Clinical Terms Australian extension,15

Types of Relationships Modified

A large variety (43) of relationship types are involved in the edits, most are IS A, and some are not part of the approved concept model or are attributes specific to an extension.
 

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Additional Observations

The following observations are only exemplars of the observations made, and by no means comprehensive.

Extensions vs Editions

Of the 9 releases looked at:

• Four publish Editions
• Three publish Extensions
• One publishes three separate extensions.
• One publishes an extension, "bundled" with the International Edition.

File naming

The file naming conventions, do not appear to be consistent across the extensions.

•  sct2_Concept_Snapshot_AU1000036_20161231.txt
•  sct2_Concept_Snapshot_en-CanadianExtension_20161031.txt
• sct2_Concept_Snapshot_DK1000005_20161130.txt
• sct2_Concept_Snapshot_LT1000092_20151107.txt
• sct2_Concept_Snapshot_NL_20160930.txt
• sct2_Concept_Snapshot_SE1000052_20161130.txt
• sct2_Concept_Snapshot_GB1000000_20161001.txt
• sct2_Concept_Snapshot_US1000124_20160901.txt
• sct2_Concept_Snapshot_es-UruguayExtension_20161215.txt
• sct2_Concept_Snapshot_INT_20160731.txt

Directory structure

Some variation was noticed in the the directory structure within the published zip files.
Below are the paths the the snapshot concepts file in each release. 

• \SnomedCT_Release_AU1000036_20161231\RF2Release\Snapshot\Terminology
• \SnomedCT_Canadian_EnglishExtension_Release_20161031\Snapshot\Terminology
• \SnomedCT_ManagedServiceDK_Production_DK1000005_20161130\Snapshot\Terminology
• \SnomedCT_RF2Release_LT1000092_20151107\Snapshot\Terminology
• \SnomedCT_Netherlands_EditionRelease_20160930\Snapshot\Terminology
• \SnomedCT_SE_Production_20161130T170000\Snapshot\Terminology
• \SnomedCT_RF2Release_GB1000000_20161001\Snapshot\Terminology
• \SnomedCT_RF2Release_US1000124_20160901\Snapshot\Terminology
• \SnomedCT_Uruguay_Extension_Release_20161215\Snapshot\Terminology

Specific file inclusions

The international release includes 6 files - Concepts, Description, Relationship,StatedRelationship,Identifier and TextDefinition files - within the "Terminology Folder"
The files are not consistently present in extensions.

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Denmark and USA are the countries to include all 6 files.
Further variations are present within the refset subdirectories.

Miscellaneous QA issues

The description file for one extension for found to be missing the language code for 268 entries. (The country was notified and have rectified).

Anchor
Conclusion Conclusion

Conclusion

• The analysis described above is reveals a wealth of information. There is evidence of duplication of content in almost every hierarchy, the extent of which likely to be much greater given the primitive analysis techniques used.
• There is value to the whole SNOMED CT community to introduce a process for content to be promoted through to core. This process should honour the identifiers issued by an extension builder, so as to minimise maintenance burden of the originating extension, and recognising their effort. The current process is prohibitive to promoting content, and consequently content is duplicated across extensions, the potential maintenance debt grows.
• Almost all NRCs are actively modifying core content. Which proves the importance of clarifying the issues raised in the Discussion Paper - Allowance of Extensions to Modify Core Content (SNOMED International Response). It seems Members have taken a different interpretation of the license to that held by the governing body, and this discrepancy has never been recognised.
• Variations in the artefacts published by NRCs exist. No comment is made about compliance with Technical Specifications, but such variances may impact portability of software that consumes SNOMED CT. Some sort of certification/verification process asserting a minimum conformance criteria would prove valuable.
• All the issues described here may just as likely apply to other (affiliate) extensions, however will remain unknown without systematic investigation.
• The issues described are real and Members are currently struggling to deal with. Prolonging their resolution introduces a cost to all.

Endnotes