It seems to be a routine MediCare requirement; CGM requires T1. IRC (I think this was discussed on another thread) the various immunological tests are also fine, CPT: 86337, for example:
The C-peptide should be CPT: 84681, based on the recent papers; a glucagon stimulation test, e.g.:
Notice that the CPT code is just some kind of “user friendly” code for a diagnostic test; so the actual tests performed may vary and may, so far as I can see, be completely useless.
The OP’s question is somewhat different; MediCare seem to accept past results, apparently BCBS are not prepared to accept anyone else’s BCBS, or even their own?