Medicare determines the provider's specialty based on how you complete the CMS-855I enrollment application and there is a separate specialty available for pain management on the form. So if your providers are enrolled with different specialties, you should not have a problem billing as a new patient if they are new to that particular specialty in your office. Other payers may have a different process - many will use the specialty that is listed on the provider's NPI registry but even that is not a certainty. In my experience, there is no sure way to know how a payer will handle new vs. established in every case. My approach has been to follow CPT guidelines and payer policies as best you can and then appeal any denials you may get.