Chiropractic billing for Medicare patients has one rule that separates compliant billing from the most common source of denials: the AT modifier. Miss it on a single claim, and that claim denies. Miss it systematically, and you have both a revenue problem and a potential compliance exposure — because the AT modifier is what distinguishes active treatment from maintenance care, and maintenance care is not covered by Medicare.
The AT Modifier: Why 31% of Chiropractic Medicare Denials Come From Here
Medicare covers chiropractic manipulation only for subluxation with a treatment goal of restoring or improving function — active care. Medicare does not cover manipulation when the goal is maintenance of current status — maintenance care. The AT modifier (Active Treatment) is how the biller signals to Medicare that this is active care.
Claims for chiropractic manipulation without the AT modifier are automatically denied by Medicare. The denial code is CO-4 (incorrect code) or a claim-level rejection. The fix is simple: add the AT modifier to every chiropractic manipulation code (98940, 98941, 98942) on every Medicare claim where the treatment goal is active and documented.
The complication: adding AT when the documentation doesn’t support active care goals is not just a billing error — it’s a false claim. The AT modifier certifies that active care is being provided. If the clinical notes describe maintenance-level treatment, billing AT creates compliance exposure. This is why chiropractic billing requires a biller who understands the documentation requirements, not just the code requirement.
Active Care vs. Maintenance Care Documentation
Medicare’s standard for active chiropractic care: the patient is showing measurable improvement, or the documentation establishes that without treatment, the patient would decline from their current functional level. Maintenance care: the patient has plateaued — continued treatment maintains but doesn’t improve function.
The billing implications are absolute: active care → AT modifier → Medicare coverage. Maintenance care → no AT modifier → no Medicare coverage. The patient is either in one category or the other, and the clinical notes must clearly establish which.
A chiropractic billing specialist reviews clinical notes before coding to ensure the documentation supports the AT modifier before it’s applied. When the documentation is ambiguous or indicates maintenance-level care, they flag for clinical review rather than defaulting to AT.
OIG Audit Focus: Chiropractic Billing
The OIG has consistently flagged chiropractic billing as a high-audit-risk area. OIG work plans have identified systematic problems with: maintenance care billed as active treatment, services billed without required documentation, and manipulation billed at higher complexity levels than documented.
OIG findings from prior chiropractic audits: approximately 64% of overpayments identified were for maintenance care billed as active treatment. The average overpayment per review was significant because the error had typically been occurring for months or years before the audit.
Frequently Asked Questions
What is the AT modifier in chiropractic billing?
The AT modifier (Active Treatment) is required on all Medicare chiropractic manipulation claims to certify that the treatment is for active care — with a goal of restoring or improving function — rather than maintenance care. Without the AT modifier, Medicare automatically denies chiropractic manipulation claims. With it applied incorrectly to maintenance care, the claim creates a false certification and compliance exposure.
Does Medicare cover chiropractic maintenance care?
No. Medicare covers chiropractic manipulation only when the treatment goal is to restore or improve function (active care). Maintenance care — treatment to maintain the patient’s current status — is not covered. When a patient transitions from active to maintenance care, Medicare billing stops. The patient may pay out-of-pocket for continued maintenance treatment, but Medicare cannot be billed.
What chiropractic CPT codes require the AT modifier?
All chiropractic spinal manipulation codes require the AT modifier for Medicare claims: 98940 (1-2 spinal regions), 98941 (3-4 spinal regions), and 98942 (5 spinal regions). The modifier is applied to the manipulation code on the claim line. No other chiropractic codes (98943 for extremity, evaluation codes) require the AT modifier.
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Related Resources
Chiropractic billing specialists | Systematic denial reduction | HIPAA compliance in billing
Our chiropractic billing specialists are trained on AT modifier requirements and CMT code compliance. We serve chiropractic practices in Illinois, Pennsylvania, and Ohio.