An ABN is a written notice that a provider/supplier gives to a Medicare patient before items or services are rendered when the provider/supplier believes Medicare probably/certainly will not pay for some or all of the items or services.
ABNs should only be provided to Medicare beneficiaries. The ABN allows the beneficiary to make an informed decision about whether to receive services that he may be financially responsible for paying. The ABN serves as proof the patient had knowledge prior to receiving the service that Medicare might not pay. If a provider does not deliver a proper ABN to the patient, the patient cannot be billed for the service.
Note: Providers may not issue ABNs to shift financial liability to a beneficiary when full payment is made through bundled payments (e.g., National Correct Coding Initiative). ABNs cannot be used when the beneficiary would otherwise not be financially liable for payments for the service because Medicare made full payment.
Note: The newly revised ABN replaces the following notices: 
 ABN-G (CMS-R-131-G).
 ABN-L (CMS-R-131-L).
 Notice of Excluded Medicare Benefits (NEMB) (CMS-20007).
*      When a valid ABN has been given, the provider is free to bill the patient for the denied services.
*      If an ABN is not valid, the provider may not bill the patient for the services. 
*      ABNs may not be used to bill patients for services that are denied as bundled into other payments.