An Advance Beneficiary Notice (ABN) is one of the few pieces of paperwork in Medicare billing that directly determines whether your practice gets to bill the patient at all when a claim is denied. Get the timing or the form wrong, and you don’t just risk a denial — you lose the right to collect from the patient too, even if the denial itself was legitimate.
What an ABN actually does
An ABN (Form CMS-R-131) is a written notice given to a Medicare patient before a service is furnished, informing them that Medicare is expected to deny payment for that specific service and that they’ll be personally responsible for the cost if it’s denied. Without a valid ABN on file for a service you reasonably expected Medicare to deny, you generally can’t bill the patient after the fact — your practice absorbs the loss entirely.
The 2026 form update — a deadline you may have already missed
CMS approved an updated version of the ABN form on March 13, 2026. The revised form became effective immediately and carries an expiration date of March 31, 2029. A transition period allowed practices to keep using the older form temporarily, but that grace period ended on May 12, 2026 — after that date, using the old form version is a compliance gap, not just an outdated template. If your practice hasn’t specifically checked which ABN version is loaded into your EHR or printed in your front-desk materials since mid-2026, that’s worth confirming directly rather than assuming it’s current.
Timing rules that actually matter
The ABN has to be signed and dated before the service is delivered — not after, and not on the same visit after the service already happened. A post-service signature is treated as invalid and won’t hold up under audit scrutiny, which defeats the entire purpose of having the form. Practically, this means your front-desk or intake workflow needs to flag likely-denial services early enough in the visit that the ABN can be presented, explained, and signed before anything is performed.
The four modifiers: GA, GX, GY, GZ
Once the ABN situation is handled, the claim itself needs the right modifier to communicate what happened:
- GA — a mandatory ABN was issued as required, and it’s on file. This is what protects your ability to bill the patient if Medicare denies the claim.
- GX — a voluntary ABN was issued for a service Medicare never covers under any circumstances (routine physicals, certain cosmetic procedures) — not required, but a good practice for transparency.
- GY — no ABN was needed because the service is statutorily excluded from Medicare coverage entirely; there’s nothing to appeal or dispute.
- GZ — you expected Medicare to deny the service as not medically necessary, but you did not issue an ABN. This is the modifier that signals “billing at our own risk” — and it means the patient cannot be billed if the claim denies. The practice absorbs the full loss.
What happens if you get it wrong
Missing the correct modifier, or skipping the ABN altogether when one was required, has the same practical effect: you lose the ability to collect from the patient once Medicare denies the claim, and the financial responsibility stays with your practice. Using an outdated or incorrectly completed form can create the same problem even if you technically had the patient sign something — if it doesn’t meet CMS’s current form and timing requirements, it may not hold up if the patient disputes the charge or the claim is audited.
Takeaway
An ABN only protects your practice’s ability to bill the patient if it’s the current form version, signed and dated before the service, and paired with the correct modifier on the claim. With the form update that took effect in 2026, this is a good moment to confirm your intake materials and EHR templates are actually current rather than assuming last year’s version still applies.