ABN: Advance Beneficiary Notice of Noncoverage
An Advance Beneficiary Notice of Noncoverage (ABN, CMS form CMS-R-131) is a written notice given to an Original Medicare patient before a service Medicare is expected to deny, shifting financial liability to the patient. A valid ABN names the specific service, the reason Medicare may deny, and a cost estimate, and must be signed before the service.
- Enforced by
- CMS (Original Medicare)
- Applies to
- Original Medicare fee-for-service patients
- Penalty
- Invalid ABN = write-off + refund exposure
What is an ABN?
An Advance Beneficiary Notice of Noncoverage is the form you give an Original Medicare patient before a service you expect Medicare to deny as not reasonable and necessary. Signed properly, it shifts financial responsibility to the patient, so a denial you would otherwise eat becomes a collectible balance. It is CMS form CMS-R-131 and its use is tightly regulated.
The ABN is the practical mechanism behind medical necessity at the point of care: it lets you deliver a service the patient wants even when coverage is doubtful, without absorbing the cost.
What makes an ABN valid?
Four things must be present, or the ABN is worthless on audit: the current CMS form, the specific service named, the specific reason Medicare is expected to deny, and a good-faith cost estimate. It must be signed before the service. Example: a patient wants a vitamin D test with only a routine screening diagnosis; you present an ABN naming the test, explaining Medicare covers it only for listed conditions, estimating the cost, and the patient signs before the draw.
Which modifiers go with an ABN?
| Modifier | Meaning | Result |
|---|---|---|
| GA | ABN on file, service expected to deny | Denies PR — bill the patient |
| GX | Voluntary ABN, statutorily excluded item | Denies PR — patient liable |
| GY | Statutorily excluded (never covered) | Denies — patient liable, no ABN needed |
| GZ | Expected denial, NO ABN obtained | Denies CO — write off, cannot bill patient |
What are the common mistakes?
Frequently asked questions
An ABN is used for Original Medicare (fee-for-service) patients when you expect Medicare to deny a service as not reasonable and necessary, or as otherwise not covered in that situation. It is not used for Medicare Advantage plans, which have their own notice processes, and it is not needed for services that are statutorily never covered (those use a different, voluntary notice).
A valid ABN must be the current CMS-R-131 form, name the specific service or item, state the specific reason Medicare is expected to deny it, include a good-faith cost estimate, and be signed and dated by the patient before the service is furnished. Blanket ABNs signed at check-in for "anything Medicare might not cover" are invalid and will be voided on audit.
Modifier GA means a valid ABN is on file, so the denial returns as patient responsibility (PR) and you can bill the patient. Modifier GZ means you expected the denial but did not obtain an ABN — the claim denies as provider liability (CO), you cannot bill the patient, and you must write it off. GA lets you collect; GZ does not.
Sources & further reading
Reviewed by the ImmediCare Solutions RCM team
Certified billers and coders handling claims across 50+ specialties nationwide. This entry is reviewed against current payer policy and CMS rules. Last review: Jul 5, 2026.
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