### Usage Notes

**Profile specific implementation guidance:**

- The scope of patient internal identifier and MRN differ in that:
  - An MRN uniquely identifies a patient in a specific institution (e.g. a hospital), and is intended to be referenced and shared by different applications within that institution. An MRN is assigned and managed by an assigning application (e.g. a Patient Master Index).  
  - A patient internal identifier uniquely identifies a patient within an application, and is not intended to be broadly shared with other applications. 
- When constructing local identifiers such as a patient internal identifier, see the guidance in [Business Identifiers](generalguidance.html#business-identifiers).


