Index code
A “code representing an entry in a standard ontology, e.g., SNOMED or RadLex, which can be applied to a finding or attribute. This is used to standardize the representation of findings and attributes across different systems and to facilitate interoperability between different systems.”1 The shape is three fields: system, code, and an optional display.
Index codes may sit on a finding model, on an attribute, or on an individual attribute value. The same type also carries a finding model’s anatomic_locations, so an anatomic location reference on a finding model is structurally an index code, usually with system: "RADLEX".1
The systems most used in the corpus are SNOMED CT, RadLex, and Gamuts, with RadElement appearing on CDE-derived definitions.2
Synonyms and near-synonyms
- Coding in FHIR is the analogous triple of
system,code, anddisplay. The CDE-labeled FHIR Observation pattern uses it the same way. - Standard code and ontology code are informal names for the same thing.
- Index code is not a crosswalk. It asserts a reference, not an equivalence class across systems.
Identifier form
None of its own. The code inside follows the referenced system, for example RID28473 for RadLex or RDES254 for RadElement.
Where it is used
Ontologies used and Finding model format.
Conflicts
The in-flight metadata rewrite tightens the rule to say that a canonical index_codes entry “must be an exact match or a clinically substitutable near-equivalent for the full model concept,” sending broader, narrower, and complication-specific codes to a separate review artifact instead.3 The corpus on main predates that rule. Separately, the CDE Set schema constrains an index code system to RADLEX, SNOMEDCT, or LOINC while the RadElement API does not appear to constrain it, and OIFM does not constrain it either.4