If the MD is only cosigning the note, I would submit the billing under the ARNP. If the MD adds additional documentation to show that they were face-to-face with the patient and also documents a "substantive portion" of the visit, then it can be billed under the MD. Per the CMS IOM, "A substantive portion of an E/M visit involves all or some portion of the history, exam, or medical decision-making key components of an E/M service." CMS IOM Publication 100-04, Chapter 12, Section 30.6.1B