Medicare: Modifiers

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The ACA receives a lot of questions about how and when to use Medicare modifiers. Knowing the answer to these questions requires some understanding of certain regulations.   

Under Medicare, the only covered service for doctors of chiropractic is manual manipulation of the spine to correct a subluxation, and only active care (acute and chronic) is reimbursable. Maintenance care is not reimbursable, although it is still spinal manipulation and, therefore, still a “covered” service. (For the exact definitions of acute, chronic, and maintenance care, consult the Medicare section of the ACA Chiropractic Coding Solutions Manual or visit Chapter 15 of the Medicare Benefit Policy Manual, §240.1.3.) The critical thing to remember is that, just because a service is “covered”, it does not necessarily mean that service is “reimbursable”.

This distinction is important for many reasons but, in this instance, it is critical because this dictates the proper usage of the Medicare modifiers.

• AT modifier: Active Treatment—Used on Covered Services (Spinal CMT) Only. Active treatment consists of acute and chronic (active/corrective) care. The –AT is required (as of October 1, 2004) on active treatment 98940, 98941, 98942 and is meant to represent to Medicare that the care was medically necessary (under Medicare guidelines).  –AT would never be used on maintenance care.  Please make sure you understand the Medicare definitions of acute, chronic, and maintenance care.

• GA modifier: Advance Beneficiary Notice (ABN) on File—Used on Covered Services (Spinal CMT) Only.  The ABN is the form that is used when a covered service (spinal manipulation) is expected to be denied due to lack of medical necessity. If the treatment of a Medicare beneficiary is maintenance care, and therefore would be considered not medically necessary and not reimbursable by Medicare, you would have the patient sign an Advance Beneficiary Notice (ABN) and are required to append the GA modifier. 

• GZ modifier: Advance Beneficiary Notice (ABN) NOT on File—Used on Covered Services (Spinal CMT) Only.  Use this modifier when an ABN should have been signed, but wasn’t. This modifier is a measure of good faith towards Medicare that you recognize you made an error.  Please note that you may NOT collect payment from the patient.

• GY modifier: Non-Covered Service (Services Which Are Statutorily Excluded or Do Not Meet the Definition of Any Medicare Benefit)—Used on All Non-Covered Services (anything NOT spinal CMT).  This modifier is required on all services other than manual manipulation of the spine, including x-rays, extra-spinal CMT, therapy modalities, and exams. Please note that you do not use GY on maintenance care spinal CMT.

• GP modifier: Services Delivered Under an Outpatient Physical Therapy Plan of Care—Used on Therapy Services Only.  This modifier is required on most therapy codes (consult the ACA Chiropractic Coding Solutions Manual, Medicare Section, for a complete list or consult the Medicare FAQ), and would be used in addition to the GY modifier (e.g., 97035 GPGY). Please note this does not mean therapy services are reimbursable if delivered by a doctor of chiropractic.

• GX modifier: Item or service expected to be denied because it is not a covered service—ABN signed.  Modifier GX went into effect April 5, 2010. The GX modifier will be used when providers want to indicate they have used an ABN to voluntarily notify a beneficiary that a statutorily non-covered Medicare service will not be covered. It is important to remember that Medicare only requires the ABN be used to inform beneficiaries when services will be denied as “not reasonable and necessary” (e.g., maintenance care spinal CMT). Providers are not required to inform patients that non-covered services (e.g., exams, x-rays, physical medicine services) will not be covered.


1) You have treated a patient with maintenance care spinal CMT.  Is it reimbursable under Medicare?

a) Yes.
b) No.

Answer: b.

2) You have treated a patient for maintenance care spinal CMT and you know it isn’t reimbursable under Medicare. You also have a properly executed ABN on file. Which modifier(s) do you append to the code?

a) –AT
b) –GA
c) –GZ

Answer: b.

3) You have treated a patient for properly documented chronic care (hence, active) spinal CMT. Which modifier(s) do you append to the code and is it reimbursable?

a) –AT and yes
b) –GA and yes
c) –GY and no

Answer: a.

4) You are billing Medicare for therapy services, which you know are statutorily excluded for doctors of chiropractic. Which modifier(s) do you append to the code?

a) –GP
b) –GY
c) –GPGY

Answer: c.