Question: If our physicians add a new doctor to the practice and the doctor is not credentialed with Medicare, how can we bill services given to Medicare patients by the new doctor? Maine Subscriber Answer: You should not use another credentialed doctors unique physician identification number (UPIN) on the new doctors Medicare claims. Some practices hold all the new doctors claims until credentialing is complete, and then submit them. Before doing that, you should ask your Medicare carrier whether that is permissible. A carrier may sometimes permit a special surrogate number for the UPIN, as with residents or interns. Ask your carrier if any surrogate numbers apply to your situation. Another option is to have the doctor only see non-Medicare patients until the Medicare credentialing process is complete. Medicare carriers can take six months or longer to complete credentialing, so if your practice is expecting a new physician, start the process well before the arrival date so claims can be submitted promptly.