Personal Health Device Implementation Guide, published by HL7 International / Health Care Devices. This guide is not an authorized publication; it is the continuous build for version 1.1.0 built by the FHIR (HL7® FHIR® Standard) CI Build. This version is based on the current content of https://github.com/HL7/phd/ and changes regularly. See the Directory of published versions

Nomenclature codes

IEEE 11073 uses nomenclature codes to represent an entity that needs to be machine readable such as a type or what the measurement is. Nomenclature codes are 32-bit unsigned integers. The most significant 16 bits give the partition and the least significant 16 bits give the term code. Partitions group the term codes into sets with a common meaning. For example, in PHD there is a health and fitness partition which groups terms associated with health and fitness, such as term codes for activities like run, bike, swim, altitude gained, distance, etc.

Associated with each 32-bit code is a reference identifier. The reference identifier is a 'semi-' human readable string such as MDC_ECG_HEART_RATE which is easier for the human reader to understand than the associated nomenclature code 147842. However, these reference identifiers are typically not provided by a PHD. Consequently, this guide does not require the encoder to include them in the FHIR mapping though it is encouraged. A second reason reference identifiers are not required is that is not possible for the encoder to send them if it encounters data from future PHDs using codes it does not know. The new codes can still be mapped to FHIR, but the reference identifiers require the encoder to have an internal map. Not requiring the reference identifiers allows the encoder to work with these future PHDs. Supporting future compatibility is one of the reasons this guide uses a generic mapping approach.

In FHIR, the 32-bit value of the code is always used. If in the PHD to PHG exchange sometimes a 16-bit code is used when the partition can be inferred from the attribute to decrease bandwidth. In these situations the encoder must convert the 16-bit value to the appropriate 32-bit value.

In IEEE 11073 Units are also encoded as nomenclature codes. HL7 and IHE favor the use of UCUM for units. This guide requires IEEE 11073 nomenclature codes for units to be mapped to the equivalent UCUM code. To maintain future compatibility, the use of the MDC nomenclature code is allowed if a UCUM code for the MDC term did not exist, or was not used by PHD standards, at the time the encoder was written.

The set of nomenclature codes is extensive, but it is segmented by partitions. Many of the codes used in the PHD measurement types and measurement values (when codes) come from the SCADA, INFRA, SITES, PHD_DM, PHD_HF, and PHD_AI partitions. This guide does not restrict the codes to come from only those partitions for future compatibility reasons. New partitions could be added and those codes could be used in future PHD specializations. Since the codes are provided by the PHD, the uploader does not need to maintain a code dictionary unless it wants to include the reference identifier or display text about the code. If this guide were to restrict the allowable codes to a given set of partitions, that restriction would prevent an older implementation from working with future devices when it otherwise could have worked with the device. It is clear, however, that any consumer and interpreter of the uploaded information would need to know about the new codes.

More information describing the MDC coding system can be found here

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