Abn
Having a patient sign an ABN protects your ability to bill the patient when you expect Medicare will not pay for the service.
from the CMS ABN Guidelines:
https://www.cms.gov/Outreach-and-Education/.../abn_booklet_icn006266.pdf
You must issue an ABN when you expect Medicare
may deny payment for an item or service because:
™™ It is not considered reasonable and necessary
under Medicare Program standards;
™™ The care is considered custodial;
™™ Outpatient therapy services are in excess of
therapy cap amounts and do not qualify for
a therapy cap exception;
™™ A beneficiary is not terminally ill (for
hospice providers only); or
™™ A beneficiary is not homebound or there is no need for
intermittent skilled nursing care (for home health
services only).
If you don't issue an ABN:
When an ABN is required and you do not issue an ABN or
Medicare finds that the ABN is invalid and you knew, or should
have known, that Medicare would not pay for a usually covered
item or service, you may be financially liable if Medicare does
not pay. You cannot collect funds from the beneficiary. If you
previously collected payment from the beneficiary, you must
refund the beneficiary the proper amount in a timely manner.
And make sure you use the correct modifier on any service provided to a beneficiary. The modifiers related to ABNs are GA, GX. GY and GZ. They are explained in the pdf link above.
I think these rules cover participating providers and non-participating ones. Somewhere on the CMS ABN website you can download a editable ABN that you can customize to your office and services provided.
There is a lot of info about ABNs on the web. Most of it easier to understand than the CMS sources. Maybe there's a professional state organization that has info for you.
Good luck!