Recording and protecting Member ID when it's the same as SSN

We’re working with a company who maintains and exchanges a member and subscriber ID along with member and subscriber SSN. However, member and subscriber IDs are exactly the same as their SSNs. We want to populate the patient resource with both identifiers for members and subscribers, however, I can’t determine which “type” to use (SS vs EI).

How can we correctly label the field as employee number while still preserving an indication that the field is SSN and should be treated with extreme care?


I guess Identifier.system has enough information to show that the identifier is an SSN and needs to be protected appropriately.