Actually, in this case, I wouldn't charge for the PA's ER visit at all, according to the coding guidelines for inpatient intial hospital care codes. Go to your CPT book and read the paragraphs above the 99221 code to see what I mean. I posted it below for you, too. Unless you are a critical care hospital, you should only bill for the initial hospital. Citical care hospitals would bill for both.
Inpatient hospital care E/M codes
CPT Assistant, April 2003 Pages: 26-27 Category: Coding Consultation
Related Information
Evaluation and Management Services/Initial Hospital Care
The admitting physician may report a code from the Inpatient Hospital Care series, 99221-99223. When the patient is admitted to the hospital as an inpatient in the course of an encounter in another site of service (eg, hospital emergency department, observation status in a hospital, physician's office, nursing facility) all evaluation and management services provided by that physician in conjunction with that admission are considered part of the initial hospital care when performed on the same date as the admission. The inpatient care level of service reported by the admitting physician should include the services related to the admission he/she provided in the other sites of service as well as in the inpatient setting.
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I know it sounds confusing because the PA is not the admitting doc, but since they are both part of the same practice, and it was all considered as the same encounter, it doesn't matter. It is considered to be the same. Hope this helps.