Terminology Approach

The PS-CA specification promotes two simultaneous goals for terminology. It promotes standardized Canadian terminologies in use today for the purpose of facilitating semantic interoperability within and across jurisdictions through the exchange of patient summaries. These are referred to as the Proposed Pan-Canadian Value Sets.

The PS-CA specification also encourages global interoperability where possible for international exchange. Value sets that have been defined by the HL7® FHIR® Base Standard or by the IPS Specification for the purposes of interoperable international exchange are referred to as the Global Value Sets. The SNOMED CT Global Patient Set (GPS) Value Sets are included in this category.

  • Note: The GPS value sets, while helpful for exchange of summaries with countries that do not have SNOMED CT licenses, are not intended to reflect the breadth and complexity of other SNOMED CT value sets used in clinical care today.

Work towards developing PS-CA version 1.0 focuses on standard terminologies available in the current landscape. Where a jurisdiction uses an alternative terminology that is different from the proposed Pan-Canadian Value Sets (local terms that are from an alternative standard, or non-standardized, value set), these are identified as Local Value Sets.

The work to identify all three types of terminology provides the basis to understand the gap between "current state" terminology/value set implementation and desired future state alignment to nationally and internationally recommended terminologies and value sets.

Given these goals, this guide employs a number of profiling mechanisms to socialize terminologies in use locally and facilitate the implementation of standardized terminologies in use nationally and globally.

Terminology Mechanisms

Terminology Binding at Element Level

Profile elements with coded datatypes (e.g., code, Coding, CodeableConcept) often have bindings to FHIR ValueSets noted in their StructureDefinitions. The strength of these bindings (required, extensible, preferred, or example) help implementers determine conformance expectations for what values should be used for the element.

Currently, this specification applies a preferred binding on the Proposed Pan-Canadian Value Sets, when feasible. While earlier versions of the specification inherited a preferred binding to the global value sets from IPS-UV, early feedback from the implementer community outlined the need to prioritize domestic jurisdictional—rather than international—exchange in Version 1.0.

Terminology Slicing

Slicing is another mechanism this specification uses to define the terminology that implementers can expect will be used in patient summaries. This specification uses slices to encourage alignment to standardized terminologies.

Slicing also provides the structure on which additional information (implementor notes) and constraints (e.g., Must Support flags, cardinality, invariants) can be layered on. This structure, when combined with terminology services, is the backbone for terminology conformance validation.

Slices put forth in this guide are open (i.e., slicing.rules is not closed), which means that it is permissible for a patient summary to use non-standard content (e.g., local concept, text only) that does not match the defined slices and still be conformant with the profile if they satisfy the remaining profile constraints. See the IPS-UV Design page for additional examples.

Multiple Codings to Represent a CodeableConcept

The ability to supply multiple codings for a given CodeableConcept is highlighted in this guide to ensure implementors have a way of supplying the original term that was captured.

This is particularly useful for elements that have a value set mandated by the FHIR R4 standard, but are anticipated to be captured in Canadian systems using an alternative terminology. One example of this is the AllergyIntolerance.clinicalStatus element. FHIR R4 standard requires the use of the AllergyIntolerance Clinical Status Codes value set which includes three concepts: active, inactive, resolved. Canadian systems implementing V3 ActStatus concepts for allergy capture (e.g., Newfoundland) will map to those three concepts but will likely also want to supply the original coding which may provide additional detail. An example of how this would be modelled in a patient summary can be found below.

"clinicalStatus" : {
    "coding" : [
      {
        "system" : "http://terminology.hl7.org/CodeSystem/allergyintolerance-clinical",
        "code" : "resolved"
      },
      {
        "system" : "http://terminology.hl7.org/CodeSystem/v3-ActStatus",
        "code" : "completed"
      }
    ]
},

Must Support Flags

Must Support flags are used in combination with slices to identify which standard terminologies vendors are expected to demonstrate they can support for a given release and/or use case. In this release, Must Support flags are only applied to the Data Absent Reason slices as this is a fundamental concept that every implementer is expected to be able to support.

As the specification evolves, implementers should anticipate that additional Must Support flags may be added to other slices to support future use cases that may have additional terminology requirements (e.g., global exchange with a country without a SNOMED CT license).

Stub ValueSets for Exposing Terminology

Stub value sets are another mechanism used in this guide to create a resource with pointers to referenced ValueSets that are not available at their canonical URL or on the terminology servers used in IG publication (i.e., tx.fhir.org).

While these stub value sets cannot be used in conformance testing (see Known Issues & Future Development ), these stand-ins allow for additional details to be provided, such as the website pages where implementors can find and download the value sets in their entirety (e.g., Terminology Gateway, Canadian Vaccine Catalogue).

Terminology Selection and Approach to Value Sets

The scope of PS-CA value sets is confined to HL7 IPS FHIR profiles that have existing terminology bindings defined for data elements. The following principles were used to guide the development and definition of the value sets required for the PS-CA profiles.

The PS-CA value sets have to:

  • Support semantic interoperability and implementation in Canada over the short- and long-term.
  • Align and support national terminology policy such as SNOMED CT Canadian Edition, Canadian Clinical Drug Data Set (CCDD), and pan-Canadian LOINC Observation Code Database (pCLOCD) (see below).
  • Accommodate the requirements of jurisdictions where feasible.
  • Take into consideration the guidance from the Global Digital Health Partnership (GDHP), which recommends the use of SNOMED CT in specific clinical domains.
  • Take into consideration the terminology binding strength of existing required value sets to ensure there is no disruption in interoperability.
  • Take into consideration that FHIR is a data interoperability standard and value sets developed are suited for data exchange and may be broader than value sets used at the point of care.
  • Include clinical review and stakeholder input and quality assurance processes.
  • Include formal documentation of the approach, decisions, characteristics of these value sets, and maintenance processes.
  • Identify opportunities for multi-use value sets, where a single value set is relevant for multiple data elements (create once, use many times).

Terminologies and Classifications - Current and Future State

Current state health system clinical terminologies and classifications identified as national standards and in use across jurisdictions include:

  • SNOMED CT Canadian Edition (SNOMED CT-CA)
  • International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, Canada (ICD-10-CA)
  • International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM)
  • Canadian Classification of Health Interventions (CCI)
  • Logical Observation Identifiers Names and Codes (LOINC)
  • pan-Canadian LOINC Observation Code Database (pCLOCD)
  • Canadian Clinical Drug Data Set (CCDD)
  • Licensed natural Health Products Database (LNHPD)
  • HL7 Vocabulary

In addition, across jurisdictions there is extensive use of free-text and locally defined term sets used for health information data capture.

In the future, it is expected these major terminologies and classifications will continue to exist and that there will be an increase in the use of SNOMED CT-CA in place of free-text or locally defined term sets for health information exchange and data capture.

Terminology Management

Terminology owners often update their code systems and value sets over time: retiring concepts, adding new ones, modifying relationships, etc. Consistent with common FHIR practice, and general best practice, terminologies used in this Implementation Guide should be "current at time of application," except when specific versions of CodeSystems or ValueSets have been identified within PS-CA. Implementers should be cautious of recognizing only the terminology in effect at the time of publication of the PS-CA Implementation Guide, or only the terminology in effect at time of system implementation. PS-CA Patient Summary documents should use current-at-time-of-creation terminology. However, since Patient Summary documents may have an extended life, recipient systems should be designed to accommodate out-of-date codes.

This release of the PS-CA Implementation Guide does not specify conformance expectations around terminology versioning (support of specific terminology versions, handling of obsolete concepts, etc.); however, future updates to the guide, or conformance programs, may define specific requirements.