Final answer:
CMS rules require providers to give an Advance Beneficiary Notice of Noncoverage (ABN) to patients when services or items may not be covered by Medicare, informing them of potential costs.
Step-by-step explanation:
In the context of healthcare services, CMS rules require the provider to present an Advance Beneficiary Notice of Noncoverage (ABN) to a patient when the provider believes that Medicare may deny payment for the specific service or item. The ABN is a written notice that providers and suppliers must provide to a Medicare beneficiary when the provider believes that Medicare will not pay for an item or service. It's important to note that the ABN must be presented prior to performing the service that may not be covered, giving the beneficiary the choice to receive and pay for the service out-of-pocket or refuse the service.