How do I get Primary Key name from GetSchema (no replies)

I am trying to retrieve the name of Primary Key constraints with either of the following:

_connection.GetSchema("IndexColumns");
or
_connection.GetSchema("Indexes");

This returns the primary key information however the INDEX_NAME column always contains the value PRIMARY rather than the name of the Primary Key constraint. Is this a bug? Or is there another way to get the Primary Key name?

Thanks