Chiropractic Billing Services

The AT Modifier and the Maintenance-Care Denial Loop

Here is the short version. Medicare pays for spinal manipulation only when it is active treatment of a subluxation, and the AT modifier is how you tell the payer that. But AT is a claim, not proof. When your note does not document active care with an expectation of functional improvement, the same claim gets read as maintenance, the AT is disallowed, and CPT 98940 through 98942 denies for medical necessity. That is the loop. This page traces exactly where a claim clears it and where it falls in.

Sec. 240

Medicare Benefit Policy Manual, Ch.15, chiropractic coverage rules

Active Treatment modifier, required on every covered manipulation line

98940–42

The only three CPT codes Medicare recognizes for CMT

The rule in one breath

AT does not mean covered. It means you are asserting active care.

Medicare Benefit Policy Manual Chapter 15, Section 240 limits chiropractic coverage to manual manipulation of the spine to correct a subluxation. Section 240.1.3 splits every case into two buckets: active or corrective treatment, which is payable, and maintenance therapy, which is not. The AT modifier signals the first bucket. It is the fastest thing to add and the fastest thing to lose in an audit, because reviewers do not check the modifier. They check whether the documentation earns it.

Pain / tenderness

evaluated and re-checked

Asymmetry / misalignment

section or segment level

Range of motion

abnormality documented

Tissue / tone changes

palpated and noted

Section 240.1.2 asks for the PART exam to demonstrate subluxation: two of the four criteria, and at least one must be Asymmetry or Range of motion. Miss that, and the acute story never gets off the ground.

The unique angle · process flow

One claim, one fork: where AT documentation clears the denial and where it triggers it

Follow a single 98941 line from encounter to adjudication. Every claim runs the same path. The fork is not the modifier you keyed. It is what the note says underneath it.

Step 01 · Encounter

Patient presents, DC performs the adjustment

Spinal CMT delivered. Regions counted for code selection.

Step 02 · Subluxation

PART exam documents the subluxation

Two of four PART findings, one being A or R. Primary diagnosis coded to the subluxation level, secondary to the neuromusculoskeletal condition.

Step 03 · Code + modifier

98940 / 98941 / 98942 keyed with AT appended

AT tells Medicare this is active treatment, not maintenance.

The medical-necessity fork

Does the note prove active, corrective care with expected improvement?

CLEARS AT holds

Treatment plan states objective goals and a measurable functional target.
Each visit records progress or the reason care continues toward recovery.
Acute or chronic subluxation with a clear aggravation or new injury.
Claim adjudicates and pays under Section 240.

TRIGGERS AT is disallowed

Note reads as supportive or preventive care, no expected improvement.
Repetitive visits with static findings and no functional change.
Plan of care never defined a discharge goal.
Reviewer reclassifies as maintenance. CO-50 / medical necessity denial.

↻

The loop closes when the practice re-bills the same static note with AT still attached. Nothing about the modifier changed, so the reclassification repeats. Breaking out means changing the documentation or moving the patient to a self-pay maintenance plan with an ABN and the GA modifier on file.

Clears vs triggers

What the two paths look like in the chart

✓ The note that clears

Initial visit captures history, the subluxation by PART, symptoms, diagnosis, and the date the current episode began, per Section 240.1.3.
Treatment plan names the specific level, the technique, frequency, duration, and an objective goal you can discharge against.
Subsequent visits document review of symptoms, changes since last visit, and progress toward the functional target.
AT modifier present on every 98940 to 98942 line, because active treatment is what the note actually shows.

✗ The note that triggers

Copy-forward visits where PART findings never move and no new complaint appears.
Plan of care with no endpoint, so care reads as ongoing wellness rather than correction.
AT appended by default in the billing software regardless of what the encounter documents.
Maintenance visits billed to Medicare without an ABN, leaving the practice, not the patient, holding the write-off.

Code reference

The three CPT codes Section 240 recognizes

Medicare covers only these for chiropractic manipulative treatment of the spine. Region count drives the code. The AT modifier logic above applies identically to all three.

CPT	Spinal regions	Descriptor	Modifier expectation
98940	1 to 2 regions	CMT, spinal, one to two regions	AT for active care; GA / GZ if maintenance
98941	3 to 4 regions	CMT, spinal, three to four regions	AT for active care; GA / GZ if maintenance
98942	5 regions	CMT, spinal, five regions	AT for active care; GA / GZ if maintenance

A quick reminder that costs practices real money: 98943 (extraspinal CMT) is statutorily excluded from Medicare regardless of modifier. When a payer follows Medicare rules, that line is patient responsibility from the start, not an appeal you can win.

Cite the source, win the appeal

The 2026 guidance your appeals should name by hand

CMS

Medicare Benefit Policy Manual, Chapter 15, Section 240 — Chiropractic Services. Defines covered manual manipulation of the spine to correct subluxation, and Section 240.1.3 draws the active-treatment versus maintenance-therapy line your AT modifier is answering.

CMS

Medicare Claims Processing Manual, Chapter 12 — AT modifier instruction. Requires the AT modifier on covered chiropractic manipulation and directs contractors to deny maintenance care. The modifier does not itself establish medical necessity.

CPT 2026

AMA CPT 2026 code set, 98940 to 98943. Current descriptors and region definitions for spinal and extraspinal chiropractic manipulative treatment.

CMS-1500

Medicare Physician Fee Schedule Final Rule for CY 2026. Sets the payment amounts and the ongoing coding and documentation expectations that your covered 98940 to 98942 lines are adjudicated against.

ABN

Advance Beneficiary Notice (Form CMS-R-131) with GA or GZ modifiers. The compliant path for maintenance visits: notify the patient in advance, capture the ABN, and route financial responsibility correctly instead of re-billing a note that will keep denying.

Your denials are not a modifier problem. They are a documentation-to-modifier gap.

ASP-RCM Solutions builds chiropractic billing services around exactly this fork. We audit where AT is attached against what each note actually documents, tighten the plan-of-care language that clears medical necessity, and set up the ABN and GA workflow so maintenance care stops draining your active-treatment collections. The result is fewer CO-50 reversals and a cleaner first-pass rate on 98940 through 98942.

Get a chiropractic denial audit →

Operator to operator. We work the same claim edits your team does, at scale.