Question: One of our doctors treated a patient for an abscess at the site of an arteriovenous (AV) fistula, and a week later the patient returned for her follow-up. She was treated by a nurse practitioner, and we want to bill the service incident-to the physician, but that particular doctor was not in that day another doctor was. Can we still bill this incident-to? And if so, under which doctor's number should we bill the service? Ohio Subscriber Answer: Although there is some disagreement about this, your best bet is to bill under the provider identification number (PIN) of the doctor who is physically present in the office suite. This is what CMS has stated as well. Medicare allows you to bill services incident-to a physician even if the service is a follow-up to one that a different doctor provided in other words, you can bill incident-to Dr. X even if Dr. X has never seen this particular patient, as long as you meet the other incident-to requirements. In addition, you should bill under the number of the doctor who is in the office because, should you be audited, you will be able to prove that this doctor was at the office that day and provided the necessary supervision. If you bill under the number of the original doctor, you won't be able to prove that he was there (because he wasn't), and you could be put in a noncompliant situation with the auditors. Answers to Reader Questions provided by Catherine Brink, CMM, CPC, principal of HealthCare Resource Management Inc. in Spring Lake, N.J.; and Patrick Cafferty, PA-C, MPAS, president of Neurosurgical Associates of Western Kentucky in Paducah.