SNOMEDCT Usage in NHS CFH HL7 Templates

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SNOMED-CT Usage in NHS CFH HL7 Templates
Data Standards and Products

• Ian Townend
• ian.townend_at_nhs.net

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Contents

• CfH Use of HL7
• Message Implementation Manual (MIM)
• CDA Documents
• CFH Templates
• User of SNOMED-CT in Templates
• TermInfo

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Contents

• Subsets
• Subset Development Process
• Current Subsets in Use
• Current Subsets in Development
• Publication Format and Availability

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Message Implementation Manual (MIM)

• The MIM is published by NHS CfH and provides the
  data specifications for each message/document
  used on the Spine.
• It is split into Implementation Manuals (IMs)
  with one for each domain e.g. Discharge.
• It also contains other artefacts which support
  the domains e.g. vocabulary.

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MIM Walkthrough
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Clinical Document Architecture

• CDA is a HL7 Standard which is currently being
  progressed through ISO.
• It gives the specification for clinical documents
  in a generic way.
• It has been adopted by CfH as the format for all
  clinical domains (except GP Summary)
• It is further constrained by CfH to meet our
  specific business needs using Templates.

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Document Structure

• CDA Documents are split into
• Header
• Administrative information such as document type,
  author, version etc
• Body
• Text sections which can be nested and optionally
  coded
• Entry
• The coded entries which contain the structured
  data used for machine processing. This is where
  the SNOMED content is carried.

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CDA Walkthrough
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Templates

• Templates represent re-usable individual
  components of information which can be combined
  to build larger structures.
• They apply further constraints and are applied as
  an overlay onto HL7 models including CDA
  documents and messages.

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Templates
Generic class
Template
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Additional constraints are applied to all
attributes to either constrain or remove the
attribute. Constraints include fixed values,
changes in cardinality, data type specialisation,
vocabulary specifications etc.
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Templates Implementation

• Templates can be implemented in a number of ways
• XML Schema based on HL7 RMIMs
• Conformance Documents
• Schematrons
• NHS CfH make most use of the XML Schema method to
  enforce the constraints.

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Templates Walkthrough
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SNOMED CT

• SNOMED CT is the Systematised Nomenclature Of
  MEDicine Clinical Terms.
• It is a comprehensive clinical terminology.
• It provides for attributes for detailing
  refinement of concepts.
• It is based on a concept model which details all
  the relationships.
• It has been adopted by NHS CfH for communicating
  clinical concepts to the Spine.

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SNOMED CT

• SNOMED CT is governed by the IHTSDO
  (International Healthcare Terminology Standards
  Development Organisation)
• In the UK, it is maintained by the UK TC (United
  Kingdom Terminology Centre) hosted by NHS CfH
• NHS CfH release SNOMED content twice a year
  (April and October) including international
  content as national extensions

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SNOMED CT Structure

• SNOMED is a polyhierarchical ontology
• It consists of a root concept (SNOMED CT) and
  child nodes which divide the content into e.g.
  findings, social contexts etc
• These are related with IS A relationships, e.g.
  asthma IS A disease of the respiratory system

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SNOMED-CT Usage in Templates

• SNOMED data may be carried in a number of
  attributes in HL7 models, the most common being
  code and value.

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SNOMED-CT Usage in Templates

• Each of these attributes is bound to a vocabulary
  which is included in the MIM
• Each SNOMED vocabulary is then bound to a subset
  using the subsets original ID
• For example

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Finding Template
FindingSnCT Vocabulary
Finding Subset
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SNOMED-CT Usage in Templates

• The actual content from SNOMED when used with any
  attribute is represented using the datatypes
• Coded Value
• Allows code, codeSystem, displayName and
  originalText.
• Concept Descriptor
• Allows code, codeSystem, displayName,
  originalText and qualifier.

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Post Co-Ordination in the Templates

• Post co-ordination is achieved using the CD data
  type as previously shown.
• The qualifier is used to hold the post
  co-ordinations.
• These contain
• A name element which represents the SNOMED
  linkage concept (e.g. laterality)
• A value element which represents the SNOMED value
  concept (e.g. left)
• New ISO standard for data types in healthcare
  will remove qualifier from the structure.

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Example

• Elective planned left hip replacement

ltcode code"405613005" codeSystem"2.16.840.1.1138
83.2.1.3.2.4.15" displayName"Planned
procedure"gt ltqualifiergt ltname
code"363589002" displayName"Associated
procedure"/gt ltvalue code"52734007"
displayName"Total replacement of hip"gt
ltqualifiergt ltname
code"272741003" displayName"Laterality"/gt
ltvalue code"7771000"
displayName"Left"/gt lt/qualifiergt
ltqualifiergt ltname
code"260870009" displayName"Priority"/gt
ltvalue code"103390000"
displayName"Elective"/gt lt/qualifiergt
lt/valuegt lt/qualifiergt lt/codegt
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TermInfo

• TermInfo is a HL7 project sponsored by the HL7
  Vocabulary Work Group
• Started in 2004 after a growing interesting the
  use of SNOMED CT by the HL7 community
• 2 initial work packages
• WP1 Specification of a general approach to
  resolving issues related to the interface between
  HL7 information models and terminologies or code
  systems
• WP2 A guide on the use of SNOMED CT concepts in
  the HL7 Version 3 communication standards

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TermInfo

• Second work package is currently in a Draft
  Standard for Trial Use (DSTU) within HL7
• Currently comments are being received for
  discussion at HL7
• For further information see http//www.hl7.org/Sp
  ecial/committees/terminfo/index.cfm

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TermInfo Details

• The guide deals with details regarding the
  overlap between the information model and the
  terminology.
• If a single possible way exists then this is
  presented as normative, else if several ways
  exist then the advantages/disadvantages of each
  are discussed

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TermInfo Section 2

• This section is the core of the standard
• It provides a detailed walkthrough of RIM
  attribute vs. SNOMED CT properties such as
• Act.classCode
• Act.code and Observation.value
• Procedure.targetSiteCode
• etc

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TermInfo Section 2

• In addition it deals with
• ActRelationships
• Representing relationships between statements
• Participations
• Subject participation
• Specimens
• Products and Consumable roles
• Context Conduction
• HL7 conduction and relevance to SNOMED expressions

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TermInfo Section 2 Example

• As an example we will consider the HL7 attribute
  Procedure.targetSiteCode which represents the
  site in which the procedure is carried out.
• This overlaps with the SNOMED attribute procedure
  site.
• So the two representations are

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TermInfo Section 2 Example
Code 397956004 (Hip replacement) targetSiteCode
362907004 (Left hip joint structure)
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TermInfo Section 2 Example

• In this case, either method could be used to
  represent the same concept of a hip replacement
  of the left hip.
• TermInfo guidance states that in this example,
  the use of targetSiteCode is not permitted.

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Subsets

• Subsets are groups of concepts taken from SNOMED
  CT that are put together for a particular use
• Within NHS CfH they are bound to a vocabulary
  which is bound to an information model
• They may also be used for other purposes such as
  including constraining choice e.g. for national
  datasets, encouraging structured entry and
  supporting background processes for decision
  support

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Subsets

• Subsets are not necessarily mutually exclusive
• They may overlap in content or one might be an
  amalgamation of others
• There is no limit on the size of subsets
• A subset may contain 1 member or 1000 members

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Subsets

• Subsets can be as generic or specific as needed.
  For example
• Radiologists might want a diagnostic imaging
  subset
• Radiologists and nuclear medicine specialists
  might want a radionuclide imaging subset
• Radiologists and nuclear medicine specialists in
  conjunction with neurologists might want a
  neuro-imaging radionuclide procedure subset

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Subset Development Process

• A process to manage the development of subsets is
  used
• There are a number of stages which the documents
  around the authoring are taken prior to the
  subsets being validated and published for use

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Subset Development Process
Review
Requirements Analysis
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Authoring
Publication
ClinicalValidation
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Subset Authoring

• Subsets are authored by constructing subset
  queries which specify which codes to include in
  the subset
• The query is saved for future use as it is the
  basis of the list
• When executed the system will return all concepts
  matching the query

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Subset Authoring

• When constructing the query, ID is specified
  along with what the ID means and an operation.
• The options are
• Single Concept
• Sub hierarchy (from that concept)
• Subset
• Along with operations
• Union
• Intersection
• Minus

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Subset Authoring

• It is also possible to specify other constraints
  on the set such as
• Status
• Language
• Locale
• Descriptions
• Relationships

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Sample Subset Query

• Employment Status subset

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Current Subsets

• There is a large list of current subsets which
  includes

Temperature Alcohol Intake Allergy
Propensity Medication Administration Smoking Lifes
tyle Social or Personal Circumstance Diagnosis Fin
ding Blood Pressure
Weight Height Investigation Treatment Family
History Risk to Patient Service Patient
Movement Provision of Advice and
Information Adverse Reaction Event
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Currently in Development

• There are a number of subsets which are currently
  in development including

Activities of Daily Living Finances Employment
Status Occupation Accommodation
Type Accommodation Tenure Pain Sleep Mood Mobility
Cognition Swallowing and Oral Health Communication
Breathing Consciousness and Seizures Skin Care
and Wound Management General Physical
Wellbeing Housing Care Plan Assessment
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Publication

• The SNOMED CT subsets published by NHS CfH are
  distributed as part of the SNOMED release through
  TRUD.
• They are distributed as flat files which contain
  lists of codes and descriptions along with other
  information such as status.

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Questions?
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