GA modifier: Waiver of liability statement on file
Category: Modifier
By Dr. Daniel Turner, DC · Reviewed September 2, 2026
What is GA modifier used for?
The modifier that tells Medicare an Advance Beneficiary Notice is signed and on file for a service expected to be denied as not reasonable and necessary. It shifts financial liability to the patient, who agreed in writing to pay if Medicare declines.
How it works in a chiropractic practice
The maintenance care modifier. When a Medicare patient continues adjustments past the active treatment window, the honest claim carries the CMT code with GA instead of AT, backed by a properly executed ABN. Medicare denies the line as expected, the denial arrives as patient responsibility rather than a contractual writeoff, and the practice bills the patient at its rate. Without the GA and the ABN behind it, the same denial forbids balance billing entirely.
What the note must show
- ✓A completed ABN, Form CMS-R-131, signed before the service was furnished, specific about the service and the reason Medicare is expected to deny
- ✓One ABN can cover a course of maintenance care when it describes the frequency and duration, but blanket ABNs signed at intake for everything forever are invalid
- ✓The claim line carries GA in place of AT; the two are mutually exclusive on the same line
A worked example
A patient with resolved low back pain wants a monthly adjustment. The practice issues an ABN describing maintenance spinal manipulation at the practice rate, the patient signs, and each visit bills 98940 with GA. Medicare denies to patient responsibility under PR-204 or the maintenance denial, the statement goes to the patient, and everyone is exactly where they agreed to be. Skip the ABN and the same claim comes back CO-50, contractual, unbillable.
Does Medicare pay chiropractors for GA modifier?
Defined by Medicare ABN policy. The companion GX modifier exists for voluntary notices on services that are statutorily excluded rather than merely not medically necessary; for chiropractic that means GX rides on excluded services like therapy codes, while GA belongs on covered but not currently necessary spinal CMT.
Where practices get burned
Billing maintenance visits with AT because it pays; blanket ABNs; GA without a retrievable signed ABN, which fails audit; confusing GA with GX and GY on the excluded services.
How Cervica helps with GA modifier
Cervica's claim scrubber validates modifiers, units, and diagnosis pointers for GA modifier before submission, per payer rules handle code substitutions and modifier requirements automatically, and when a payer pushes back anyway the denial worklist reads the adjustment codes and routes the claim to the exact fix.
Related codes
- →AT modifier · Active treatment modifier for Medicare CMT
- →GY modifier · Statutorily excluded service
- →98940 · Chiropractic manipulative treatment, spinal, one to two regions
- →CO-50 · the denial this code most often triggers
Quick answers
What is GA modifier used for?
The modifier that tells Medicare an Advance Beneficiary Notice is signed and on file for a service expected to be denied as not reasonable and necessary. It shifts financial liability to the patient, who agreed in writing to pay if Medicare declines.
What documentation does GA modifier require?
A completed ABN, Form CMS-R-131, signed before the service was furnished, specific about the service and the reason Medicare is expected to deny One ABN can cover a course of maintenance care when it describes the frequency and duration, but blanket ABNs signed at intake for everything forever are invalid The claim line carries GA in place of AT; the two are mutually exclusive on the same line
Does Medicare pay chiropractors for GA modifier?
Defined by Medicare ABN policy. The companion GX modifier exists for voluntary notices on services that are statutorily excluded rather than merely not medically necessary; for chiropractic that means GX rides on excluded services like therapy codes, while GA belongs on covered but not currently necessary spinal CMT.
References
General information for billing teams, not legal, coding, or payer specific advice. CPT is a registered trademark of the American Medical Association; code descriptions here are paraphrased in our own words and the AMA's CPT publications control. Payer policies vary and control for any individual claim.