Which mechanism is used to implement requirements that are not part of the core FHIR specification?

• A. Profile Extensions
• B. Security Extensions
• C. Resource Extensions
• D. User Extensions

Answer: (C)

Extensions are the mechanism to capture information not described in the core FHIR resources. When a local requirement isn’t part of the standard, you define an Extension (with a unique URL) and attach it to a resource as a Resource Extension. This lets you include additional data while keeping the core resource definitions stable and interoperable across systems. Profiles constrain or refine existing elements of resources, rather than adding new data fields, so they’re not the mechanism for implementing new, non-core requirements. Security Extensions and User Extensions aren’t standard mechanisms in FHIR for this purpose.