A value transmitted in a field of data type HD must contain what?

In the context of HL7 messages, the data type HD, which stands for "Hierarchic Designator," is used to represent specific codes and their corresponding coding systems. The correct answer indicates that a value transmitted in a field of data type HD must contain both a local code and an external coding system ID.

This requirement stems from the structure of the HD data type, which is designed to provide a comprehensive and unambiguous way to communicate coded values. The local code helps identify a specific entity within a local context, while the external coding system ID refers to a recognized coding system outside this local context, ensuring consistency and interoperability across different systems.

By incorporating both the local code and the external coding system identifier, it allows users to fully understand the meaning of the code and where it comes from, which is vital for the accurate exchange of health information. This level of detail aids in reducing ambiguities that can arise when similar codes exist in different systems or when a local code might not be universally recognized.

Other options do not fully meet the requirements of the HD data type. For instance, only having a code from a local table doesn't provide sufficient context for the code's meaning to those outside of that local environment. Similarly, specifying only the external code