Chiropractic ABN & modifiers
Chiropractic ABN (Advance Beneficiary Notice): When and How to Use It
Medicare won’t pay for maintenance care, but whether the patient can be billed for it comes down to one form, signed before the visit. Here’s the rule, the modifiers, and how we keep it clean.
What an ABN is
An ABN is the one piece of paper that decides who pays when Medicare won’t.
An Advance Beneficiary Notice of Noncoverage (ABN), the standardized Form CMS-R-131, is a written notice you give a Medicare patient before a service you expect Medicare to deny. It tells the patient, in plain language, that Medicare probably won’t pay, why, and roughly what it will cost, so they can decide whether to proceed and accept financial responsibility. Signed correctly and on time, it transfers liability to the patient. Skipped or done wrong, the cost lands on the practice.
For a chiropractor, the ABN matters more than for almost any other specialty, because the Medicare chiropractic benefit is unusually narrow, and the line it draws runs right through the middle of a typical treatment plan. This guide covers what the ABN is, the coverage rule that triggers it, mandatory versus voluntary notices, the modifiers (GA, GZ, GX/GY) that pair with it, how to fill the form out, and the mistakes that quietly cost practices money. It sits underneath our full chiropractic billing service; for the broader claim rules behind it, see our chiropractic Medicare billing guide and the CPT codes & modifiers cheat sheet.
A general reference, not legal or billing advice. ABN rules, the CMS-R-131 form, and Medicare coverage policy change, and the right notice always depends on the specific service and patient. Use this to orient, then verify against the current CMS ABN instructions and your MAC’s policy before you rely on it. Nothing here is legal, compliance, or coding advice for a particular claim.
Coverage rule
Medicare covers active, corrective adjustment, and never maintenance.
Under the chiropractic benefit, Medicare Part B pays for exactly one thing: manual manipulation of the spine to correct a subluxation (CPT 98940, 98941, and 98942), and only when it is active, corrective care, flagged with the AT modifier (Active/Corrective Treatment). The moment the goal shifts from improving the condition to simply holding the patient where they are, the care becomes maintenance, and Medicare won’t pay for it.
That is not a billing glitch you can modifier your way around. It is a coverage line written into the benefit. When you expect a service to be denied because it’s maintenance (or otherwise non-covered), you issue the ABN before the visit so the patient can choose to pay. The ABN doesn’t make Medicare pay; it makes the patient billable when Medicare doesn’t. That’s the whole point.
Note the difference in those two lines below the top one. Maintenance spinal CMT is a covered code that’s expected to be denied as not medically necessary, so the ABN is mandatory. Extraspinal 98943 is statutorily excluded (never a benefit), so the ABN there is voluntary. Same form, two different paths, and the modifier follows the path. We cover both next.
Mandatory vs. voluntary
Mandatory vs. voluntary ABN, and why the distinction matters.
Not every non-covered service triggers the same obligation. The form is identical; what changes is whether issuing it is required to protect your right to bill the patient, or simply a courtesy that prevents a surprise. Getting this wrong in either direction (skipping a required notice, or issuing a blanket one on everything) is where practices get hurt.
Covered service, expected denial
Required when a normally covered service, like spinal CMT, is expected to be denied as not reasonable and necessary. The classic case: continued adjustment that has become maintenance care. Without a valid ABN, you generally cannot transfer liability to the patient when the denial lands.
Pairs with the GA modifier. This is the notice chiropractors use most.
Statutorily excluded service
Optional (but recommended) for services Medicare never covers under the chiropractic benefit, such as extraspinal manipulation (98943), exams, X-rays, and therapies billed by the DC. The patient is already liable by statute; the ABN is a courtesy that documents they were told up front.
Reported with GY (statutorily excluded); add GX when a voluntary ABN is on file.
Why it’s worth getting right: a mandatory ABN you forget to issue means a maintenance visit you can’t bill to anyone: a pure write-off. A voluntary ABN you skip on 98943 usually still leaves the patient liable, but invites a billing dispute you didn’t need. The form costs you sixty seconds at check-in; the missing form can cost the whole visit.
Modifiers
GA, GZ, GX, GY: the ABN’s shorthand on the claim.
A modifier tells Medicare the status of the notice behind the line. Most of them describe what you did with the ABN, and one of them, used wrong, makes the service unbillable to anyone. They are not interchangeable, and on a chiropractic claim they decide whether a denied service becomes patient revenue or a write-off.
GA · the one you want
Signals a signed, mandatory ABN is on file for a covered service expected to be denied: maintenance CMT. It transfers liability so you can bill the patient when Medicare denies. This is the modifier that turns a non-covered maintenance visit into legitimate patient revenue.
GZ · the costly one
Means you expect a denial but have no ABN on file. Lines billed with GZ are auto-denied (CO-50), and you cannot bill the patient. The practice eats it. GZ isn’t a strategy; it’s an honest admission that a step was missed.
GX / GY · the excluded one
A statutorily excluded item carries GY (item never a Medicare benefit), and extraspinal 98943 is the textbook example. When you also hand the patient a voluntary ABN, add GX alongside it, so the line reads GX/GY. The patient is already liable by statute; the notice just documents they were told.
Never put AT and GA on the same line. They describe opposite things: AT says “active, covered care,” GA says “expected denial, ABN on file.” A claim can’t be both. MACs return CMT lines submitted with both AT and GA together to be corrected and resubmitted rather than appealed. A visit is either active care billed to Medicare (AT), or maintenance billed to the patient with an ABN (GA). One or the other, every time.
Completing the form
A valid ABN names the service, the reason, and the cost, and is signed before the visit.
For an ABN to actually transfer liability, three blanks have to be filled in honestly and specifically, and the patient has to sign before the service. Hand it over at check-in, walk the patient through it, and let them choose an option. You cannot pre-check a box or complete the signature line for them.
The form spells out the service in patient-friendly terms (the adjustment, the extraspinal manipulation), the reason it’s expected to be non-covered (“Medicare does not pay for maintenance chiropractic care”), and a good-faith estimated cost. A blank cost estimate can invalidate the whole notice, so the estimate has to be reasonable. CMS expects it within $100 or 25% of the actual charge. The patient then picks an option, signs, and dates it. That signed, pre-service form is what makes the GA (or GX) modifier mean anything.
Two billing tracks
Two clean tracks, never blurred.
Everything above collapses into a simple operating rule. Active care and non-covered care run on two separate tracks, and the only job is to put each visit on the right one, with the documentation, the notice, and the modifier all telling the same story.
Billed to Medicare
Billed to the patient
Where a patient sits on that line (active vs. maintenance) is a clinical decision the provider documents. The billing job is to make sure the claim matches the chart: AT on the visits the note supports as active care, an ABN and GA on maintenance, and GY (with a voluntary ABN and GX) on excluded items. We never quietly add AT to make a denial disappear, and we never let a maintenance visit go out without the notice that protects it.
Common mistakes
The three ABN mistakes that cost the most.
Almost every ABN problem traces back to a handful of habits. None of them are exotic. They’re the shortcuts a busy front desk takes, repeated on every patient until they add up to real money.
Blanket / routine ABNs
Handing every Medicare patient an ABN “just in case” (or a single signed form meant to cover all future visits) isn’t a valid notice. A routine or blanket ABN doesn’t transfer liability, and it can read as a sign the practice doesn’t know which services are actually covered. Each notice has to be tied to a specific expected denial.
Missing it on maintenance care
The opposite failure: a patient transitions from active to maintenance care, but the visits keep going out as active, or with no ABN at all. When Medicare denies, there’s no signed notice to bill the patient against, and the visit becomes a write-off. The maintenance transition is exactly when the ABN has to appear.
GZ instead of a real ABN
Reaching for the GZ modifier (“expect denial, no ABN”) instead of obtaining the notice. The line auto-denies CO-50 and can’t be billed to the patient. GZ is what you report when the step was genuinely missed, not a substitute for doing it. The fix is always upstream: get the ABN signed before the visit.
The thread running through all three: the ABN is only as good as the timing and the specificity. Signed before the service, tied to a real expected denial, with a true cost estimate, it protects the practice. Backdated, blanket, or replaced by a GZ shortcut, it doesn’t. For how this sits alongside the rest of the claim, see our claim denials guide and the full chiropractic billing guides.
How we help
Every visit gets sorted onto the right track before the claim goes out.
The AT-vs-maintenance call is clinical, but making sure the notice, the modifier, and the claim all agree with that call is billing work, and it’s exactly what we do. We check each Medicare CMT visit against the same questions on this page so active care is billed to Medicare with AT, and maintenance or excluded care carries a valid ABN and the right modifier before it’s billed to the patient.
And it’s consultative, not just defensive. The same review that keeps your ABN and modifier usage clean also catches the money generalists miss: undercharged E/M visits, codes left off the claim, lines priced below the fee schedule. Many of our clients run multi-specialty centers, so the same coordinator also bills the therapy, massage, acupuncture, and nurse-practitioner visits under your roof, with the Medicare-specific rules applied correctly across all of them. It’s the same scrutiny that runs through our full billing service, all one flat fee, laid out on our pricing page.
Proof
The expertise shows up in the collections.
“In practice over 30 years, I have never found a more professional, knowledgeable company. I have a dedicated person accessible at all times, and they’re compatible with my EHR so I have no extra steps.”
“ACB has been instrumental in cleaning up our accounts receivable, helping us transition between software, and staying on top of all our billing. Knowledgeable, and most importantly, effective.”
“I used to spend a lot of time calling insurance companies when claims weren’t paid. Now they’re part of my team, so I can focus on patient care. Highly recommend.”
FAQ
Chiropractic ABNs, answered.
An Advance Beneficiary Notice of Noncoverage (ABN), the standardized Form CMS-R-131, is a written notice you give a Medicare patient before a service you expect Medicare to deny. It explains that Medicare likely won’t pay, why, and the estimated cost, so the patient can decide to proceed and accept responsibility. Chiropractors use it most when continued spinal manipulation has become maintenance care (which Medicare doesn’t cover) and for statutorily excluded services like extraspinal manipulation (98943). Signed before the visit, it lets you bill the patient when Medicare denies.
An ABN is mandatory when a normally covered service, like spinal CMT, is expected to be denied as not reasonable and necessary, the classic case being maintenance care. Without it, you generally can’t bill the patient after the denial. An ABN is voluntary for services Medicare never covers under the chiropractic benefit (statutorily excluded items like extraspinal 98943, which carry the GY modifier); the patient is already liable, so the notice is a courtesy that documents they were told up front. The form is the same; the obligation and the modifier differ.
GA means a mandatory ABN is on file for a covered service expected to be denied; it transfers liability so you can bill the patient. GZ means you expect a denial but have no ABN on file; those lines are auto-denied (CO-50) and cannot be billed to the patient, so the practice absorbs the cost. GY reports a statutorily excluded item that is never a Medicare benefit, such as extraspinal 98943; GX is added alongside GY when you also gave the patient a voluntary ABN. In short: GA protects you on covered-but-denied care, GX/GY handle the always-excluded items, and GZ is the one that leaves you holding the bill.
No. AT says the care is active and covered; GA says it’s expected to be denied with an ABN on file. A line can’t be both, and Medicare contractors return CMT claims billed with both AT and GA together to be corrected and resubmitted rather than appealed. Each visit is either active care billed to Medicare with AT, or maintenance care billed to the patient with an ABN and GA. Never both on the same line.
List the specific service in patient-friendly terms, the reason Medicare is expected not to pay (for example, “Medicare does not pay for maintenance chiropractic care”), and a good-faith estimated cost. CMS expects the estimate within $100 or 25% of the actual charge, and a blank estimate can invalidate the notice. The patient then chooses an option, signs, and dates the form before the service is provided. You can’t pre-check the option box or sign for the patient, and a backdated, blanket, or routine ABN doesn’t transfer liability.
If the care is maintenance and you have no valid ABN, Medicare denies it as not medically necessary, and without the signed notice you generally can’t bill the patient either, so the visit becomes a write-off. Reporting the GZ modifier (“expected denial, no ABN”) just confirms that exposure: those lines auto-deny CO-50 and aren’t patient-billable. The fix is always upstream: identify the maintenance transition and get the ABN signed before the visit. That’s exactly the kind of step we keep on track.
Pricing
All of this, for 7% of net collections.
The AT-vs-maintenance review, the ABN and modifier checks, denials and appeals, your dedicated coordinator, and the consultative revenue work: it’s all included in one performance-based fee: 7% of net collections, or a $1,500/month minimum, whichever is greater. All-inclusive, month-to-month, no contract. See the full breakdown and run the numbers on our pricing page.
Official sources
Where these rules come from
The ABN rules on this page come directly from CMS. Form CMS-R-131 and its instructions are updated periodically, so always issue the current version.
- CMS: Advance Beneficiary Notice of Noncoverage (ABN, Form CMS-R-131)
- CMS: Beneficiary Notices Initiative
- CMS Billing & Coding: Chiropractic Services (A56273)
Billing rules also vary by state. See our state-by-state chiropractic billing guides. Each covers the local auto-injury, Workers’ Comp and Medicaid rules, cited to the governing statute.
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General reference, not legal or billing advice · HIPAA-regulated · BAA available · Any-EHR compatible · Month-to-month · Transparent 7%