Page Status: updated 2022-03-18
Terminologies
Page index
Introduction
The Swedish National Medication List is to a large extent based on coded values published as terminologies, later referred to as code systems and value sets. Code systems and value sets are used within elements of the type code. Coded values are used in many FHIR resources, e.g. Medication, MedicationRequest etc. to structure the information and make it system readable. The content of code systems and value sets define a set of values in a specific context. The expression code is commonly also called term or concept and is a structured and often standardized way of expressing a value e.g. mg for milligram.
A code system / value set can represent codes from a wellknown terminology e.g. Snomed CT or UCUM, or locally defined codes.
The picture below shows how the binding to code systems or value sets can be seen in a FHIR-profile elements. In this case, the profile NLLDosage has an element route (1) with a binding (2) to the value set nll-snomed-route which defines all valid codes for a route.
Value sets were the basepath of the URI starts with http://electronichealth.se or http://ehalsomyndigheten.se are defined by the Swedish eHealth Agency and can be fetched from the endpoint [base]/ValueSet. Value sets and code systems defined by other organisations are usually not republished by the Swedish eHealth Agency. The identity of a value set or code system can take many forms, e.g. OID, URI etc. An URI identity may in some cases be used as an URL as well, and make it possible to look up and view the concepts by a browser.
CodableConcept and code
The way FHIR usually uses codes in resources is by defining a CodableConcept. One single concept can be described in CodableConcept by specifing one or more codes, and/or a textual description. In some cases the use of codes in the resource is very strict, e.g. in the "status" element that is available in many resources. In those cases a plain code is used.
Resource types and relations
The figure below shows how the terminology resources relate to eachother.
Code System
A code system is a set of concepts where each concept has a unique code, a display name and possibly a definition of the conecept.
No code systems are published by the Swedish National Medication List but each value set is refering to the code system of each code in the value set.
Value Set
Most value sets in the Swedish National Medication List are subsets of larger code systems and they are published as a NLLValueSet. A value set can contain codes from more than one code system.
Some value sets contains the code OTH ("other" HL7 Nullflavor code) which represents that there are no applicable concept. In most such cases it is required to add a textual description in combination with OTH code.
Concept Map
The resource NLLConceptMap is used to show how codes in different value sets relate to each other. As an example based on the codes below, the code AME-0005 (Application) in nll-edqm-method (EDQM-based ValueSet) is related to the code 738991002 (applicera) in nll-snomed-method.
Concept maps are provided to facilitate the translation of codes from certain common code systems into the code systems used by the Swedish National Medication List.