GA, GZ, GY: billing correctly after the ABN conversation

What the three modifiers tell Medicare

GA, GZ, and GY are the three modifiers that report what happened with an Advance Beneficiary Notice of Noncoverage — the ABN, Form CMS-R-131 — before you delivered a service you expected Medicare might not pay 1Ref 1Centers for Medicare & Medicaid Services (2026).Beneficiary Notices Initiative (BNI).That the ABN (Form CMS-R-131) governs when a Medicare patient must be warned in writing that a service may be denied, and that the GA, GZ, and GY modifiers report the ABN outcome on the claim.. Each one sends a different message to the claims processor about whether coverage is in doubt, whether the patient was warned in writing, and who can be billed if the line denies. Choosing the right one is the difference between a bill you can legally send the patient and a write-off you absorb. They are not interchangeable, and the processor treats each denial differently depending on which one you appended.

When GA is the right modifier

Append GA when you expect Medicare to deny a normally covered service as not reasonable and necessary and you have a signed ABN on file for it 1Ref 1Centers for Medicare & Medicaid Services (2026).Beneficiary Notices Initiative (BNI).That the ABN (Form CMS-R-131) governs when a Medicare patient must be warned in writing that a service may be denied, and that the GA, GZ, and GY modifiers report the ABN outcome on the claim.. GA tells the processor the patient was warned in advance and accepted financial responsibility, so if the line denies, you may bill the patient. It is the modifier that protects your right to collect.

The ABN behind it has to be genuine and specific — a valid notice names the service, the reason you expect the denial, and an estimated cost — not a blanket form signed at every visit. If you are unsure whether a given service even needs the warning, the companion question of when is an abn required is worth settling before you reach for the modifier.

GZ: the modifier that means the ABN is missing

Use GZ when you expect the same denial but no ABN was obtained before the service 1Ref 1Centers for Medicare & Medicaid Services (2026).Beneficiary Notices Initiative (BNI).That the ABN (Form CMS-R-131) governs when a Medicare patient must be warned in writing that a service may be denied, and that the GA, GZ, and GY modifiers report the ABN outcome on the claim.2Ref 2Centers for Medicare & Medicaid Services (2026).Internet-Only Manuals (IOMs).That CMS's Medicare Claims Processing Manual, published in the public Internet-Only Manuals, is the operative program instruction for how a modifier is applied to a Part B claim.. GZ is an admission: you thought coverage was doubtful, you did not warn the patient in writing, and so you cannot shift the cost to them. Medicare denies a GZ line as provider-liable, and the balance becomes your write-off.

GZ exists so the claim is honest, not to help you get paid. In practice it is simply what GA becomes when the paperwork was skipped — which is the whole reason the ABN conversation belongs before the service rather than after the denial arrives.

GY: services Medicare never covers

Reach for GY when the service is excluded from Medicare by statute — something the program never covers for anyone, not merely something likely to be denied on this claim 1Ref 1Centers for Medicare & Medicaid Services (2026).Beneficiary Notices Initiative (BNI).That the ABN (Form CMS-R-131) governs when a Medicare patient must be warned in writing that a service may be denied, and that the GA, GZ, and GY modifiers report the ABN outcome on the claim.2Ref 2Centers for Medicare & Medicaid Services (2026).Internet-Only Manuals (IOMs).That CMS's Medicare Claims Processing Manual, published in the public Internet-Only Manuals, is the operative program instruction for how a modifier is applied to a Part B claim.. Because the exclusion is categorical, an ABN is not technically required, though many practices still give the patient a voluntary notice so the financial conversation is documented.

GY forces a fast, formal denial, and that denial is often the point. Coordination of benefits can only move a claim to a secondary payer once Medicare has formally denied it 3Ref 3Centers for Medicare & Medicaid Services (2026).Coordination of Benefits and Recovery Overview.That coordination of benefits sets primary-versus-secondary payer order, so a formal Medicare denial on a GY-flagged line is what lets the claim move to a secondary payer., so a GY line is frequently what starts the secondary process — including the medicaid-billing path when Medicaid sits behind Medicare — or what lets you bill the patient for a plainly non-covered item.

How to decide before you submit

Work it backward from two questions: does Medicare cover this service at all, and do you expect it to pay on this patient. If the service is statutorily excluded, the answer is GY. If it is normally covered but you expect a not-reasonable-and-necessary denial, the answer is GA with a signed ABN, or GZ without one. The Medicare Coverage Database is where you confirm whether a national coverage determination or your MAC's local coverage determination makes a denial likely 4Ref 4Centers for Medicare & Medicaid Services (2026).Medicare Coverage Database (MCD) Search.That a national coverage determination or a MAC's local coverage determination in the Medicare Coverage Database is where a clinician confirms whether a service is likely to be denied — the trigger for an ABN and a GA modifier., and the Medicare Claims Processing Manual is the operative instruction for how the modifier is actually applied to a Part B claim 2Ref 2Centers for Medicare & Medicaid Services (2026).Internet-Only Manuals (IOMs).That CMS's Medicare Claims Processing Manual, published in the public Internet-Only Manuals, is the operative program instruction for how a modifier is applied to a Part B claim.. Settling coverage first turns the modifier choice into a lookup rather than a guess.

What the wrong modifier costs

The two expensive mistakes are opposite. Bill GZ, or omit the modifier entirely, on a service you could have collected for, and you write off money the patient legally owed — because you skipped the ABN. Bill GA on a service where the ABN was defective or missing, and an auditor can find you billed a patient you had no right to bill.

Neither is fatal on a single claim, but as a pattern each one is a leak: one drains revenue you earned, the other invites a compliance problem. The fix is upstream — a real ABN conversation, keyed to a coverage check, before the visit ever happens.