Codes
Codes are used throughout CDA. There are clinical codes (medication codes, procedure codes, lab test codes, etc.) and administrative codes (gender, language, zip code, etc.).

While a human reader can match up a wide range of spellings, abbreviations, etc. as all being the same thing – a computer system generally requires a consistent identical code. So machine processing requires the use of codes rather than descriptive text to represent things.

Codes vs. Identifiers
Note that the term “code” in this context means something different than “identifier”. A “code” is something that exists in a pre-defined list that can be looked up. An “identifier” is used for something assigned continuously as new instances are created – like a driver’s license number or a mobile phone serial number. Although an identifier is also a kind of code, it’s not a “code” in the context of this article. Refer to the article Identifiers in CDA for more information about identifiers.

Code Systems
A code system is a set of codes and their assigned meaning or interpretation.

For example, the set of US Zip Codes is a code system which defines codes such as 10001 for a geographical area in Manhattan, NY. That same 10001 code could be the code for a medication, a part of the body, or anything else… in some other code system. It’s only possible to talk about the meaning of a code within the context of its code system.

Code systems can be independently maintained by third party standards organizations. This is the case for leading clinical code systems – such as SNOMED-CT, LOINC, RxNorm, ICD-9, and many others – but also general purpose code systems such as UCUM for units of measure (refer to the article The UCUM code system) and US Postal Codes. Many of the code systems used in C-CDA – especially for administrative codes – were created by (and are maintained by) HL7.

Additional Information
Refer to the article Codes in CDA for information about the XML syntax of code elements in CDA documents.

Refer to the article Value sets for an introduction to the “value set” concept that is prevalent in HL7 materials, including the CDA and C-CDA specifications, and an explanation of why most CDA PRO Know articles about codes in CDA, do not talk directly to the “value set” concept.

Other CDA PRO Know Articles Referenced In This Article