Modifier GA: Waiver of Liability (ABN on File)
The GA modifier tells Medicare a signed ABN is on file for a service that may be denied as not medically necessary. When to use GA, ABN rules, and GA vs GZ.
Modifier GA is a HCPCS Level II modifier that tells Medicare you gave the patient a valid Advance Beneficiary Notice of Non-coverage (ABN) before a service you expected Medicare to deny as not reasonable and necessary. CMS's descriptor is "Waiver of Liability Statement Issued, as Required by Payer Policy" (MLN006266). GA doesn't make the service payable; it decides who pays if Medicare denies it: with GA and a valid ABN, the patient does.
Key takeaways
- GA is for services Medicare covers but may deny in this case: medical necessity, LCD diagnosis lists, or frequency limits.
- The ABN must be signed before the service, name the specific service and give a genuine reason denial is expected. Blanket or generic notices don't count.
- Medicare still reviews a GA claim. If it pays, the patient owes only normal cost-sharing.
- No ABN means modifier GZ, and the provider is liable for a denial.
- Services Medicare never covers take GY, not GA.
Modifier GA · payment effect
With and without the modifier
G0121 without GA · national office
$378.43
Screening colonoscopy
G0121-GA · No change to the rate
$378.43
A signed ABN is on file. Medicare decides payment; if denied, the patient is liable.
When to use the GA modifier
Use GA when all of these are true:
- Medicare covers the service in general, but you expect a denial for this patient under §1862(a)(1) of the Social Security Act: the service may not be reasonable and necessary, the diagnosis isn't on the local coverage determination's list, or the service exceeds a frequency limit.
- You gave a mandatory ABN (form CMS-R-131) before the service, the patient chose an option and signed it, and you keep it on file. You don't send the ABN with the claim, but you must produce it on request.
- The claim is for traditional Medicare. Medicare Advantage plans use their own pre-service notice process.
Common GA situations for physician practices:
- A screening service done sooner than Medicare's frequency limit, such as a screening colonoscopy (G0121). CMS's ABN booklet lists preventive services that exceed frequency limits as a required-ABN case.
- A test ordered for a diagnosis the LCD doesn't support, such as vitamin D testing or an echocardiogram for an indication outside policy.
- Therapy or injections beyond what a MAC policy considers necessary.
When not to use the GA modifier
- No signed ABN. Use GZ. You can't bill the patient for a medical-necessity denial without a valid notice.
- The service is never covered (routine physical, cosmetic surgery, hearing aids). Use GY, with GX if you gave a voluntary notice.
- The ABN was signed after the service, or the patient refused to sign. An after-the-fact notice doesn't transfer liability.
- The service exceeds the therapy threshold but is medically necessary. That is KX, not GA.
How GA affects payment
GA has no payment percentage and doesn't trigger automatic payment or denial on professional claims. Medicare reviews the service normally:
- Medicare pays: the allowed amount is paid and the patient owes only their usual deductible and coinsurance. The ABN is moot.
- Medicare denies as not reasonable and necessary: the remittance assigns liability to the patient, and you may collect your charge.
- The ABN is found invalid: the MAC overrides GA and the provider is liable (ch. 30, §30.2).
Keep every ABN for five years from the date of care, including ones the patient refused to sign (MLN006266).
GA vs GZ, GY and GX
| Modifier | Covered by Medicare? | ABN | Liability if denied |
|---|---|---|---|
| GA | Yes, but denial expected | Required ABN signed and on file | Patient |
| GZ | Yes, but denial expected | No ABN | Provider |
| GY | No, excluded by statute | Not required | Patient |
| GX | No, excluded by statute | Voluntary notice given | Patient |
CMS descriptors (MLN006266): GZ "Item or Service Expected to Be Denied as Not Reasonable and Necessary"; GY "Item or Service Statutorily Excluded or Does Not Meet the Definition of Any Medicare Benefit"; GX "Notice of Liability Issued, Voluntary Under Payer Policy."
FAQ
Why do we use the GA modifier?
To tell Medicare a valid ABN is on file for a service you expected to be denied as not medically necessary. If Medicare denies it, the patient is liable instead of the provider.
What do the modifiers GA and GZ mean on a medical bill?
Both mean the provider expected Medicare to deny the service as not reasonable and necessary. GA says the patient signed an ABN, so the patient may be billed if it's denied. GZ says no ABN was obtained, so the provider absorbs the denial.
When should the GZ modifier be used?
When you expect a medical-necessity denial and didn't get a signed ABN, for example in an emergency or when the patient wasn't available to sign. GZ keeps the claim honest; the provider remains liable.
Does GA mean Medicare will deny the claim?
No. Medicare reviews a GA line like any other. If the service meets coverage rules it is paid, and the patient owes only normal cost-sharing.
What is the difference between GA and GY?
GA is for covered services that may fail medical necessity and requires an ABN. GY is for services Medicare never covers and doesn't require one.
Keep reading
- Modifier GY for statutorily excluded services.
- Modifier KX for therapy above the yearly threshold.
- Modifier GP, JW and JZ for other Medicare-specific HCPCS modifiers.
- Codes on this page: G0121 G0105 93306
Sources: CMS MLN006266, Medicare Advance Written Notices of Non-coverage (May 2025); CMS Medicare Claims Processing Manual, Pub. 100-04, ch. 30, §§30.2, 40.2.2 and 50. Verified October 6, 2026.
