GA, GZ, and GY are the three Medicare Advance Beneficiary Notice (ABN) modifiers. They live on the same claim line as the drug J-code and tell the MAC who is on the hook if Medicare denies. GA = ABN was signed, patient agreed to pay if denied. GZ = ABN was not obtained, claim will deny and patient cannot be billed. GY = service is statutorily excluded from Medicare entirely, patient is fully liable regardless of ABN. They are mutually exclusive at the line level — pick one, never two.
The Advance Beneficiary Notice of Noncoverage program is defined in CMS Internet-Only Manual Publication 100-04 (Medicare Claims Processing Manual), Chapter 30 (Financial Liability Protections), and rests on the statutory hook of Section 1879 of the Social Security Act as amended by the Balanced Budget and Improvement Act (BIPA). Section 1879 limits a Medicare beneficiary's financial liability when a service is denied as not reasonable and necessary — unless the beneficiary was given proper advance notice of likely non-coverage. The notice form is CMS-R-131, and the GA modifier is the claim-line mechanism that tells the MAC the notice was given.
Of the three modifiers, GA does the most work. It moves a Medicare-denied charge from provider write-off to patient responsibility. GZ exists as the explicit alternative for when the provider expects denial but failed to obtain (or chose not to obtain) an ABN; it produces a clean denial with no patient billing. GY is the statutory-exclusion case — the service is something Medicare never covers under any circumstance (cosmetic procedures, hearing aids, routine dental, off-pathway uses outside any Medicare benefit category) — and is often used to generate a Medicare denial that the patient can use for secondary insurance or supplemental plans.
All three modifiers are specific to Medicare and to Medicare Advantage plans that follow CMS billing convention. Commercial payers do not use this modifier set; instead they have their own member-liability waiver processes (Notice of Member Liability, advance written notice of non-coverage, network-out-of-coverage acknowledgements). Appending GA, GZ, or GY to a commercial claim is harmless but does not substitute for the commercial payer's own waiver workflow.
GY — patient is fully liable and an ABN is not legally required (though many practices issue one as a courtesy and for documentation).GA — the patient is liable if Medicare denies.GZ. Medicare denies; the patient cannot be billed. The line is a write-off. GZ exists to give the MAC the clean signal that you knew this would deny — it is not a penalty modifier, but a habit-of-use pattern (every claim carrying GZ) is an audit red flag.The cleanest mental model is two questions in sequence: (1) Is this a Medicare benefit at all? If no, GY. If yes, (2) Do I expect denial, and did I get the ABN? Yes/yes → GA, yes/no → GZ, no/either → no modifier. The GA pathway is by far the most common in oncology, ophthalmology, and infusion-clinic settings, because off-label and off-LCD scenarios arise constantly and a well-run practice routinely obtains ABNs in those situations. GZ should be rare; GY is reserved for the narrow set of services Medicare statutorily does not cover.
The ABN modifier set is Medicare-native. Commercial payers do not use GA/GZ/GY and instead require their own member-liability waiver process. The grid below covers Medicare and the four largest commercials so the practice has a one-glance reference on what these modifiers do (and do not) accomplish across the book.
| Payer | ABN modifiers recognized? | Notes |
|---|---|---|
| Medicare (Part B) | Yes — GA, GZ, GY are the source-of-truth ABN modifier set | Defined in IOM Pub 100-04, Chapter 30. GA preserves the right to bill the patient when Medicare denies as not reasonable and necessary. GZ produces a clean denial with no patient liability. GY documents statutory exclusion. MACs may add LCD-specific guidance on which ICD-10 / J-code combinations trigger ABN expectations. |
| Medicare Advantage (MA) | Generally yes — plans follow CMS billing convention | Most MA plans honor GA/GZ/GY the same as traditional Medicare and have their own Notice of Denial of Medical Coverage (NDMC) or Detailed Explanation of Non-Coverage (DENC) forms layered on top. Confirm in the specific plan's provider manual; some MA plans require their own additional integrated notice. |
| UnitedHealthcare (commercial) | Not recognized — harmless if appended, ignored at adjudication | UHC commercial uses its own member-liability waiver workflow through the patient portal and the practice's own consent forms. Append the practice's commercial-waiver form to the chart; do not rely on a Medicare GA to shift liability on a UHC commercial claim. |
| Aetna (CVS Health, commercial) | Not recognized | Aetna commercial requires a written notice of non-coverage signed by the member before rendering a non-covered service. The notice is on Aetna's own template and is filed in the chart. The Medicare GA modifier does not transfer. |
| Cigna / Express Scripts (commercial) | Not recognized | Cigna uses a Pre-Service Member Acknowledgement for known non-covered services. Accredo dispensing reports include an analogous liability acknowledgement when the patient receives a non-covered specialty drug, but the medical-claim line does not need a GA modifier. |
| Humana (commercial book) | Not recognized on commercial; recognized on Humana MA | Humana's MA-heavy book honors the ABN modifier set for the MA lines of business. Humana commercial uses its own member-liability waiver form. Be careful to flag the line of business correctly before deciding whether the GA matters. |
| Denial pattern | What it means | Fix / appeal language |
|---|---|---|
| GA used without a valid ABN on file (post-payment audit recoupment) | Medicare paid the line because GA preserved patient liability, but a post-payment audit discovered the ABN form is missing, unsigned, more than one year old, or does not list the specific item billed. The MAC recoups the paid amount AND the practice cannot bill the patient because the ABN basis was invalid. | Pull the ABN immediately. If valid, submit it with the audit response and cite IOM Pub 100-04, Chapter 30, §50.6 (ABN content requirements). If invalid, the practice absorbs the recoupment; do not back-date or re-create the ABN. Going forward, audit the ABN file monthly against GA-flagged claims to catch mismatches before the MAC does. |
| GZ as a "habit modifier" on every claim (integrity audit flag) | The MAC's data analytics flag a provider whose GZ rate is statistically anomalous — e.g., GZ on more than 5% of all Part B drug lines. Pattern suggests either chronic under-collection of ABNs (process problem) or use of GZ as a defensive default (fraud red flag). | Do not defend the pattern; fix the process. GZ should be rare. If GZ rate is high, the underlying scenario (off-label use without ABN) is being repeated and the intake workflow needs to capture an ABN at the point of order. Document the corrective process in case the MAC opens a formal review. |
| GY appended to a Medicare-covered service (incorrect denial) | GY was used on a service that is actually a covered Medicare benefit (e.g., therapeutic Botox for chronic migraine, J0585 for a covered ICD-10). Medicare denies the line as "statutorily excluded" even though the service is covered, and the patient gets billed for a service that should have been paid. | Resubmit with no GY (and GA if you anticipated possible medical-necessity denial). Appeal language: "The service rendered is a covered Medicare benefit under [LCD/NCD reference] for ICD-10 [X]. Modifier GY was appended in error; the corrected claim removes the modifier. Please re-adjudicate as a covered service." Attach the LCD coverage page showing the indication is on the covered list. |
| GA / GZ / GY appended to a commercial claim (harmless but wasted) | The practice's claim scrubber adds an ABN modifier to every potentially-questionable line, including commercial claims. The commercial payer ignores the modifier (they do not recognize GA/GZ/GY), and the practice's own commercial-waiver process may not have been completed for the same line. | No claim correction needed — the commercial payer adjudicates as if the modifier were not present. The real risk is on the chart side: confirm the commercial payer's own member-liability waiver form is on file for any service where the patient was billed for non-covered care. Going forward, scope the ABN-modifier rule in the scrubber to Medicare and Medicare Advantage payer IDs only. |
| ABN form expired (more than one year old) — GA inappropriate | Practice billed GA citing an ABN signed during a prior episode of care that is more than one year old, or the ABN covers a different drug/indication than the current line. CMS treats expired or non-matching ABNs as no ABN, so the GA-flagged line is treated like a GZ line in an audit. | Re-issue the ABN at the next encounter and re-bill subsequent lines with a fresh GA. For the already-billed line, expect post-payment recoupment if audited; do not back-date the ABN. Train intake to issue a fresh ABN at any course-of-treatment change (new drug, new indication, more than one-year duration) per IOM Pub 100-04 Chapter 30 §50.6. |
| GA and GZ on the same line (mutually exclusive pair) | Claim line has both GA and GZ appended, often because the scrubber added one and a manual edit added the other. The two modifiers describe opposite scenarios (ABN obtained vs not obtained) and cannot coexist. | Resubmit with the single correct modifier. If the ABN is valid and on file, use GA. If not, use GZ. Appeal language: "Modifiers GA and GZ are mutually exclusive per CMS IOM Pub 100-04, Chapter 30. The corrected claim retains [GA / GZ] based on the ABN documentation in the chart, dated [MM/DD/YYYY]." |
GA and GZ both signal that the provider expects Medicare to deny a service as not reasonable and necessary. The difference is documentation: GA means a valid Advance Beneficiary Notice (CMS-R-131) was signed by the patient before the service, so the patient agreed to pay out of pocket and is financially liable. GZ means no ABN was obtained, so the provider has no basis to bill the patient and the claim will be denied with no patient liability.
No. GA is a prospective expectation of denial — the provider believes the service is unlikely to meet medical necessity for this specific patient and ICD-10 combination. The MAC adjudicates the claim on the merits. If Medicare in fact pays, the GA is harmless and the patient is not billed for the Medicare-allowed portion. If Medicare denies, the GA preserves the practice's right to bill the patient because the ABN is on file.
The Advance Beneficiary Notice of Noncoverage (Form CMS-R-131) is a CMS-mandated form a Medicare provider gives a beneficiary in advance of a service the provider expects Medicare may not cover. The form must list the specific item or service, the reason Medicare may deny, and the estimated cost. The patient checks one of three options (receive and bill Medicare, receive and pay out of pocket, do not receive) and signs. The form is the precondition for billing the patient if Medicare denies as not medically necessary.
Per CMS guidance in the Medicare Claims Processing Manual, Chapter 30, a single ABN can cover an extended course of treatment for up to one year provided the items, services, and reasons for non-coverage do not change. A new ABN is required if the situation changes (different drug, different indication, different cost estimate). Practices that rely on ABNs more than one year old should re-issue; in audit, an expired ABN is treated as no ABN — and a GA modifier on top is then inappropriate.
Yes. GA, GZ, and GY may be appended to Part B drug HCPCS lines (J-codes, Q-codes) the same as to any other CPT/HCPCS service. The most common drug scenario is GA on a J-code where the drug is being used off-label or off-pathway and Medicare may deny for medical necessity. The modifier is appended at the line level for the specific drug J-code; the administration code is modified independently if applicable.
The provider documents the refusal (a second staff member witnesses, the refusal is noted on the ABN form itself, and the form is retained), and may then proceed only if willing to absorb the cost if Medicare denies. Coding-wise, if the provider proceeds and expects denial, the line is reported with GZ (no ABN on file) — the claim will deny and the patient cannot be billed. Alternatively, the provider may decline to render the service. The practice should never bill GA without a signed ABN; backdating or proceeding-as-if is an enforcement risk.
Commercial payers do not use the GA/GZ/GY modifier set — those modifiers exist specifically to communicate ABN status to Medicare. Commercial payers have analogous patient-financial-responsibility processes (Notice of Member Liability forms, advance written notice of non-coverage), but appending GA/GZ/GY to a commercial claim is harmless and ignored. Do not omit the practice's own commercial-payer waiver form on the assumption that a Medicare ABN modifier substitutes for it.
GY signals that the service itself is statutorily excluded from Medicare — it does not meet the definition of any Medicare benefit (e.g., cosmetic Botox, hearing aids, routine dental). A statutorily excluded service should always carry GY when billed to Medicare, even though Medicare will deny and patient is fully liable; the GY documents that the provider knew the exclusion and is billing for crossover/secondary purposes or to produce a Medicare denial the patient can use to seek payment elsewhere. By contrast, an ICD-10 that falls outside an LCD's covered diagnosis list is a coverage limitation (use GA with ABN), not a statutory exclusion.
All sources are publicly available federal publications or paraphrased from trade-association educational materials. The methodology by which we resolve source disagreements is described in the Methodology.