Using Codes

Many fields in FHIR are represented with coded values. The HL7 FHIR specification outlines several ways to define and use codes in resources.

Coding Systems

Codes commonly come from:

Resources used in the FHIR Interface may contain any of these coded values. CareEvolution’s internal terminology management system can associate some local terms with canonical terms, and will provide that association when available.

For example, consider the following Observation resource. Although there is a custom code of “GLU” from the DemoEMR system, it has been associated with the Glucose LOINC code. This gives you context for the code’s semantic meaning.

<code>
    <coding>
        <system value="http://fhir.carevolution.com/codes/DemoEMR/LabObservationType" />
        <code value="GLU" />
        <display value="Glucose" />
        <userSelected value="true" />
    </coding>
    <coding>
        <system value="http://loinc.org" />
        <code value="2345-7" />
        <display value="Glucose SerPl-mCnc" />
        <userSelected value="false" />
    </coding>
    <text value="Glucose" />
</code>

Even if no canonical term exists, the “text” field usually provides a human-readable representation–in this case, Glucose.

Finding System URIs

When specifying a code, you must specify a system URI, which tells where the code came from. Some examples can be seen in the coded values above:

<system value="http://loinc.org" />
<system value="http://fhir.carevolution.com/codes/DemoEMR/LabObservationType" />

Most codes will be associated with standard, widely-recognized coding systems like LOINC, SNOMED-CT, ICD-10, or NDC. A list of the standard coding systems used by the FHIR API can be found in your site’s FHIR directory.

Normally when performing FHIR operations, you will be working with codes from these standard systems. In unusual situations, you may need to translate between internal CareEvolution codes and standard codes. The system URI explorer, available through the “Search” tab of the request explorer, allows you to take an internal CareEvolution term namespace (such as “LOINC”) and convert it to the standard system URI (http://loinc.org) or vice-versa.

System URI Explorer Link
System URI Explorer Link
System URI Explorer
System URI Explorer