Chiropractic billing runs on a few rules that, once you know them, save a lot of denied claims and a lot of awkward conversations with patients. Medicare in particular has firm limits on what it pays for, and the AT modifier sits right at the center of it. So let’s walk through how chiropractic billing works with Medicare, what the AT modifier does, and how maintenance care fits in.
What Medicare Actually Covers
Medicare’s rule for chiropractic care is narrow, and a lot of billing problems start with not knowing how narrow.
Medicare pays for manual manipulation of the spine to correct a subluxation. That is it. The covered codes are 98940, 98941, and 98942, which cover spinal manipulation across different numbers of regions. Anything outside spinal manipulation, like exams, x-rays ordered by the chiropractor, or therapy modalities, is not covered under the chiropractic benefit.
This catches new billers off guard. A patient may receive several services in a visit, but Medicare will only consider the spinal manipulation, and only when it meets the rules.
The AT Modifier & Why It Matters
The AT modifier stands for Active Treatment. It is the piece that tells Medicare the manipulation was active and corrective, not maintenance.
When to Use AT
You append AT to the manipulation code when the treatment is working to improve or restore function. The patient has a condition, there is a treatment plan, and the care is moving them toward a goal. That is active care, and AT signals it.
Without the AT modifier, Medicare reads the claim as maintenance and denies it. So on any claim where you expect Medicare to pay, the AT modifier needs to be there, and the records need to support active treatment.
When Not to Use AT
Once a patient hits a plateau and the care shifts to keeping them comfortable rather than improving them, that is maintenance. You do not put AT on maintenance care, because using it on care that is not active is a compliance problem. The modifier has to match what the note shows.
Maintenance Care & the Patient Conversation
Maintenance care is where billing meets honesty with the patient. Medicare does not pay for it, but patients still want it, and they can still get it. The key is handling it correctly.
The ABN
Before you provide maintenance care to a Medicare patient, you give them an Advance Beneficiary Notice. This form tells the patient Medicare likely will not pay and that they may be responsible for the cost. The patient signs it, and now everyone knows where they stand before the care happens.
The GA Modifier
When an ABN is on file, you append the GA modifier to the claim. This tells Medicare a valid ABN exists, which means if Medicare denies the service, the patient can be billed. Skipping the ABN and the GA modifier on maintenance care leaves you unable to collect from the patient and unpaid by Medicare.
Documentation That Holds Up
Chiropractic claims get audited, and the records are what decide whether you keep the payment.
Show the Subluxation
Medicare wants the subluxation documented, either through an x-ray or through a physical exam using the PART method, which looks at Pain, Asymmetry, Range of motion, and Tissue tone. The record has to show what you found.
Spell Out the Treatment Plan
A treatment plan shows the care has a goal and an end point. It names the condition, the planned frequency, and what improvement you expect. This is what separates active care from maintenance in the eyes of a reviewer.
Track Progress Visit to Visit
Notes that change from visit to visit show the patient is improving and the care is active. Notes that read identically every time suggest maintenance, and that pulls the AT modifier into question.
Common Chiropractic Billing Denials
A few denials show up again and again in chiropractic claims.
Missing AT modifier on active care. Medicare reads it as maintenance and denies. Confirm AT is on every active treatment claim.
Maintenance billed without an ABN. With no ABN and no GA modifier, the denial leaves you stuck with no one to bill. Get the ABN signed first.
Subluxation not documented. If the record does not show the subluxation, the manipulation has nothing to support it, and the claim falls apart on review.
Non-covered services billed to Medicare without the right modifier. Exams and modalities billed as if Medicare covers them get denied. Knowing what is covered keeps these off the claim.
Putting It Together
Chiropractic billing comes down to matching the claim to the care. Active treatment gets the AT modifier and documentation that shows progress. Maintenance care gets an ABN and the GA modifier so the patient can be billed. The subluxation gets documented every time. Do those things and Medicare claims hold up, patients know what they owe before care happens, and denials stop eating into the practice’s income.