Basically, the ambulance service transporting you makes that initial decision. For Federal and State programs like Medicare and Medicaid, federal law makes it illegal for an ambulance service to bill Medicare or Medicaid for ambulance service that the ambulance service provider knows, or should have known, did not meet the government’s criteria for medical necessity. If the patient insists that the ambulance service bill Medicare, then the ambulance service is required by government regulations to use a code that notifies Medicare that the ambulance service believes that the service did not meet the medical necessity criteria.