CMS has issued an MLN Ambulance Transports Booklet. The booklet (36 pages) can be downloaded here.

Download MLN Ambulance Transports Booklet

One section of the Booklet that you might want to keep handy involves Free-Standing Emergency Departments. Specifically, on page 15, CMS states the following:

Freestanding Emergency Department (ED)
If a freestanding ED is provider based (a department of the hospital), the ambulance transport from the freestanding ED to the hospital is not a separately payable service under Part B if the beneficiary is admitted as an inpatient prior to ambulance transport. For more information about criteria for coverage of ambulance transports separately payable under Part B or as a packaged hospital inpatient service under Part A, refer to Chapter 10, Section 10.3.3, of the Medicare Benefit Policy Manual.

This may be useful, along with the Manual section cited, when you have a free-standing ED that is part of a hospital and they call for transports to the main building for the patient to be admitted, but the hospital lists the time of admission as being prior to the time of your transport. When the hospital admits the patient prior to your transport, the hospital becomes responsible for the ambulance charges. It may be useful to show the hospital and ED the booklet and Manual section to prove to them that the hospital is responsible if the patient is admitted to the hospital prior to your transport.