Final answer:
If Medicare services are known to be non-covered or excluded, providers should issue an Advance Beneficiary Notice (ABN) to inform the patient that they may be responsible for the payment.
Step-by-step explanation:
When either condition code 20 (Beneficiary requested billing) or 21 (billing for denial notice) is reported, and it is known by the provider that the services are non-covered or excluded by Medicare, the patient should have been issued a(n) Advance Beneficiary Notice (ABN). An ABN is a written notice given to Medicare beneficiaries to convey that Medicare is not likely to provide coverage for a specific service or item. This is crucial information as it informs the patient that they will likely be responsible for the payment. ABNs are especially important within a fee-for-service health financing system where providers are reimbursed according to the services they provide.