Specifications that contain queries meant to be run on the LOINC distribution or that contain intensional value set definitions should be expressed with the LOINC attributes contained in Appendix A. (In JSON representations such as HL7’s FHIR, the LOINC attribute serves as the key in an object’s property definition. Not to be confused with the LOINC notion of Property, in JSON, a key-value pair is often referred to as a property). The available LOINC attributes are the field names listed in bold in LOINC Database Structure section. Unless Regenstrief publishes a definitive specification otherwise (see discussion of canonical LOINC representation in FHIR below), these names, and their spellings, are the official attribute names. For example, specifying the set of LOINC terms with a scale of document would reference the LOINC attribute SCALE_TYP and its value of DOC.
In addition, for LOINC codes that are part of the Document Ontology or those that are radiology procedure codes, there are additional attributes that may be used in attribute-based Value Set Definition components. All attributes will have string values that may be used for the attribute (property) value part of the definition. Some will also have coded identifiers (e.g. LOINC Part codes) that can be used in addition to the string.
For Document Ontology:
- Document.Kind
- Document.TypeOfService
- Document.Setting
- Document.Role
- Document.SubjectMatterDomain
These Document Ontology attributes are currently published in the accessory Document Ontology File (available as a separate download from the LOINC website), and will likely be extended in the future. They will always be the unique values in the PartTypeName field of the Document Ontology File. Starting with the LOINC version 2.61, these are also published in the LOINC Part File artifact (also available as a separate download).
For Radiology:
- Rad.Guidance for.Presence
- Rad.Guidance for.Approach
- Rad.Guidance for.Action
- Rad.Guidance for.Object
- Rad.View.Aggregation
- Rad.View.View type
- Rad.Reason for Exam
- Rad.Maneuver.Maneuver type
- Rad.Timing
- Rad.Pharmaceutical.Substance Given
- Rad.Pharmaceutical.Route
- Rad.Anatomic Location.Region Imaged
- Rad.Anatomic Location.Laterality.Presence
- Rad.Anatomic Location.Laterality
- Rad.Anatomic Location.Imaging Focus
- Rad.Modality.Modality type
- Rad.Modality.Modality subtype
- Rad.Subject
These radiology attributes are published in the PartTypeName field of both the LOINC/RSNA Radiology Playbook File and the LOINC Part File. Both of these artifacts are available as a separate download from the LOINC website.
12.3.1 Canonical representation of LOINC as a FHIR CodeSystem
Together with the HL7 FHIR team, we are working to create a specification for the canonical representation of LOINC in FHIR as a CodeSystem resource. This is a work in progress. An initial draft of that specification is available at https://loinc.org/fhir/loinc.xml.
This specification is specific to HL7 FHIR®, and it’s definitions of the LOINC attributes would supercede the general guidance about names for attributes (properties) given above. For example, in the canonical representation for FHIR, the radiology LOINC attribute Rad.View.Aggregation will be named closer to the conventions for FHIR-style property names as “rad-view-aggregation”.