Personal Health Device Implementation Guide
1.0.0 - STU 1

Publication Build: This will be filled in by the publication tooling

## Codeable Concepts

In this guide there will be several instances where the 11073 10101 nomenclature (MDC) codes are mapped to FHIR. In almost all cases this mapping involves an element that is a CodeableConcepts data type. The mapping is as follows:

- CodeableConcept.coding.code = partition * 216 + term code
- CodeableConcept.coding.system = urn:iso:std:iso:11073:10101
- CodeableConcept.text = reference identifier (optional)

The reference identifier in the text element is optional since the uploader may not know what the code means; for example, if the uploader works with a PHD specialization developed after the uploader had been released. However, this guide strongly encourages that the text element contains at least the normative reference identifier for the MDC code if it is known.

The text element itself is also optional for future compatibility. Any text element entry requires that the uploader have some previous knowledge of the code as display information is not provided by protocol.

The text element is also used instead of the coding.display element since the latter has restrictions based upon the code system. The information in the display element must come from the code system itself, and in the case of the MDC code system only the reference identifier is defined for all codes. Consequently for this implementation guide to avoid conflicts it is suggested that the text element be populated with “reference identifier: optional additional implementation-defined text describing the code which may be in the local language”. For example, “MDC_CTXT_GLU_MEAL: Meal associated with measurement”.

The CodeableConcept is used quite frequently in other FHIR elements. It has a Coding element which specifies the code system being used to define the item. The Coding element has a 0..* cardinality which allows one to define the item or concept in several different coding systems. Its important to understand that the different coding systems must all describe the same concept, or at least be a reasonable match. In addition, the Coding.system element used to define the coding system is never a value set, but must always be a code system. One can easily be misled when examining the links in the FHIR specification that bring one to the codes a given element may use which displays a bold link but is a value set and not a code system. For example, if one clicks on the DataAbsentReason link describing the Observation.dataAbentReason element one will see the bold title http://hl7.org/fhir/ValueSet/data-absent-reason. However, this element is NOT to be used in the Coding.system element of the Observation.dataAbsentReason. A legal value for the field would be http://terminology.hl7.org/CodeSystem/data-absent-reason if one used the codes in the table from that coding system. The overall Value Set is a list of Coding Systems that maybe used in this element. However, when the code is selected, the system element takes on the code system from which that code came.

- Next: Obtaining the Observation.code
- Previous: Nomenclature Codes