From my understanding only the admitting MD for observation can bill the inital observation & subsequent codes. All other providers have to use the NEW/EST codes.
This is from Chapter 12 30.6.8 of CMS manual - Payment for an initial observation care code is for all the care rendered by the ordering physician on the date the patient’s observation services began. All other physicians who furnish consultations or additional evaluations or services while the patient is receiving hospital outpatient observation services must bill the appropriate outpatient service codes.
For example, if an internist orders observation services and asks another physician to additionally evaluate the patient, only the internist may bill the initial and subsequent observation care codes. The other physician who evaluates the patient must bill the new or established office or other outpatient visit codes as appropriate.
