The following is from CMS. Although this applies to Medicare, most, if not all, commercial payers will fall into line with this guidance.
30.6.5 - Physicians in Group Practice(Rev. 1, 10-01-03)
Physicians in the same group practice who are in the same specialty must bill and be paid as though they were a single physician. If more than one evaluation and management (face-to-face) service is provided on the same day to the same patient by the same physician or more than one physician in the same specialty in the same group, only one evaluation and management service may be reported
unless the evaluation and management services are for unrelated problems. Instead of billing separately, the physicians
should select a level of service representative of the combined visits and submit the appropriate code for that level. Physicians in the same group practice but who are in different specialties may bill and be paid without regard to their membership in the same group.
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Ryan Stroup, CPC