architecture design for application user

I have an architecture design question,

I am using asp core identity to manage my user auth and login, I also have a patient registry in my db and I their access to the db is optional. 

my question is, Shall I create another user table and separate them from database users and handle their auth separately or link the registry table to Application user table?

if linking them to the application user is the best option, I have one problem here, Registry table PK is long and my user Application PK is Guid.

I really appreciate any input

Thanks