Codings, Codeable Concepts, and Value Sets

Coding

A coding, or code set in Health Cloud, represents a specific concept in the context of the terminology system that defines that concept. Multiple codings can represent the same real-world concept. However, their form depends on the terminology systems that define them and the versions of those systems. Codings consist of five components: Code, Display, System, Version, and User Selected.

Code: The symbol that represents the concept. This code can be a string of numbers or characters, and not necessarily a word. If this attribute is absent in a coding, the terminology system has no defined code to represent that coding’s concept. Consider a code as the form of a coding.

Display: The text that represents the meaning of the code and its concept.

System: The URI of the terminology system that defines the concept of a coding. There are many terminology systems that the industry uses, like LOINC, SNOMED, RxNorm, ICD, and so on.

Version: The version of the terminology system that defines the coding. As mentioned earlier, the form a coding takes can change across versions of the terminology system.

User Selected: The boolean value that specifies whether the code is explicitly chosen by a user, as opposed to being selected by an automated algorithm. The expectation is that codings marked true for this attribute are more likely to be more accurate. If there are multiple codings that represent the same concept, codings marked true for this attribute tend to be more accurate. The Health Cloud implementation calls this attribute Primary.

Here’s what a JSON sample for a coding looks like:

<coding>
        <system value="http://snomed.info/id"/>
        <version value="International Release – 20130731"/>
        <code value="389145006"/>
        <display value="Allergic Asthma"/>
        <primary value="true"/>
    </coding>

The Health Cloud implementation of coding doesn't support hierarchies because the FHIR definition of a coding doesn’t specify hierarchies. However, if your organization requires recording hierarchies, you can do that by adding a self-reference field to the Code Set object.

Codeable Concept

A codeable concept represents a unique real-world concept that’s represented by codings. Codeable concepts bind together codings from across systems and versions, with the binding factor being the shared concept that those codings represent. For instance, let’s say that system 1 represents COVID-19 as C19 in version 2.31 and as CVD2019 in version 1.13, and system 2 represents COVID-19 as C204. The codeable concept that represents the real-world concept of COVID-19 binds all three codings together.

The Health Cloud implementation of codeable concepts, called code set bundles, allow only 15 codings to be bound together while FHIR places no such constraint on codeable concepts.

Here’s a JSON sample for a codeable concept:

<codeableConcept>
    <!-- SNOMED code -->
    <coding>
        <system value="http://snomed.info/id"/>
        <version value="International Release – 20130731"/>
        <code value="389145006"/>
        <display value="Allergic Asthma"/>
        <primary value="true"/>
    </coding>
    <!-- ICD code -->
    <coding>
        <system value="urn:oid:2.16.840.1.113883.6.42"/>
        <version value="9"/>
        <code value="493.00"/>
        <display value="Extrinsic asthma - unspecified"/>
        <primary value="false"/>
    </coding>
    <text value="Atopic Asthma"/>
</codeableConcept>

Value Set

A value set, like a codeable concept, binds together different codings. However, a value set is grouped by the context of the codings that are bound together and isn’t a shared concept that aligns across terminology systems. For instance, while a codeable concept binds together codes representing a specific illness, a value set binds together code sets representing multiple illnesses.

Health Cloud hasn’t explicitly implemented value sets using any object or component. However, to achieve a basic degree of grouping, you can group together code set records that have the same values for the Code Set Type field.