Why Is Chiropractic the Most Audited Medicare Specialty?
Chiropractic services carry the highest improper payment rate among all Medicare Part B services at 33.6 percent, according to CMS’s Comprehensive Error Rate Testing program. An OIG audit found that approximately 82 percent of Medicare chiropractic payments were for services that did not comply with Medicare requirements, primarily because maintenance care was billed as active treatment. The AT modifier, which is supposed to distinguish active care from maintenance, was found on virtually every claim the OIG flagged as improper.
- The AT modifier is a claim, not proof. The modifier attests that the visit was active treatment. It does not prove it. Documentation in the clinical note is what proves it, and that is where audits find the gap.
- Maintenance care is not covered. Medicare covers manual spinal manipulation to correct a subluxation only when the treatment is active and corrective. Treatment that maintains the current condition or prevents deterioration is not payable.
- Audits reach back years. RAC reviews, SMRC targeted reviews, and CERT audits can request documentation on claims from prior years. A billing habit that runs unchecked compounds into a multi-year liability.
What the OIG Found
The HHS Office of Inspector General has audited Medicare chiropractic payments multiple times since 2005, and the findings have been consistently severe. The most cited audit found that approximately $385.8 million of the $439 million Medicare paid for chiropractic services in the study period did not comply with Medicare requirements. The primary reason was maintenance care billed as active treatment.
What makes this finding actionable for every chiropractic practice is the AT modifier problem at its center. Medicare requires the AT modifier on every claim for active or corrective treatment. But the OIG found that almost every claim it identified as maintenance therapy still carried the AT modifier. The modifier was present; the documentation behind it was not. This is the pattern that drives the audit cycle: the modifier says active, the note says routine, and the payer pulls the claim.
In our experience matching chiropractic practices with billing partners, the practices with the highest audit exposure are not the ones doing anything unusual. They are the ones applying the AT modifier as a default rather than a clinical statement, documenting the same findings visit after visit, and treating the modifier as a billing step rather than a reflection of what the note actually says.
What Is the Difference Between Active Treatment and Maintenance Care?
This distinction decides whether Medicare pays. Active treatment is corrective care aimed at producing measurable functional improvement, documented through objective outcome measures such as pain scores, range of motion changes, or disability index results. Maintenance care is treatment that seeks to maintain the current condition, prevent deterioration, or provide comfort without expectation of further improvement. Medicare covers the first and explicitly excludes the second.
| Active Treatment (covered) | Maintenance Care (not covered) |
|---|---|
| Corrective care aimed at measurable improvement | Care to maintain or prevent deterioration |
| Objective outcomes documented (ROM, VAS, ODI) | Subjective improvement or comfort only |
| Treatment plan with goals and expected duration | Open-ended or indefinite treatment plan |
| Functional status changes visit to visit | Same findings documented repeatedly |
| AT modifier supported by the note | AT modifier applied by default |
The line between the two is drawn visit by visit in the clinical note, not at the start of a treatment plan. A patient can shift from active to maintenance mid-course, and the documentation must reflect the transition. Across the billing companies we vet, the most common audit finding is not a wrong code or a wrong modifier. It is a clinical note that looks identical from visit to visit, which tells a reviewer the care was maintenance regardless of what the modifier says. For the chiropractic CPT codes that carry the AT modifier, the documentation standard is the same across 98940, 98941, and 98942.
If your AT modifier rate is near 100 percent but your notes do not change visit to visit, your practice is in the audit profile. A billing partner who specializes in chiropractic can audit your documentation pattern and fix it before a contractor asks. Get matched with vetted chiropractic billing companies, free.
How to Audit Your Own AT Modifier Risk
Providers often come to us after a RAC or SMRC records request, when the safer move would have been to run the audit internally first. These steps identify the exposure before a payer does.
- Pull your AT modifier rate. Calculate the percentage of your Medicare CMT claims that carry the AT modifier. If it is at or near 100 percent, that pattern is the first thing a reviewer sees.
- Sample 20 to 30 charts at random. Read the notes for objective outcome measures, visit-to-visit changes, treatment goals, and expected duration. If most notes look the same, the documentation does not support the modifier.
- Check for a transition point. Identify whether any patient chart documents the moment care shifted from active to maintenance. If no chart does, the practice may be billing maintenance as active across the board.
- Count visits per patient per year. The OIG found that claims become increasingly likely to be medically unnecessary after 12 treatments per year. High-frequency patients need stronger documentation, not the same note repeated.
- Verify the ABN workflow. When a patient transitions to maintenance care, the practice should issue an Advance Beneficiary Notice (CMS-R-131, updated May 2026) before the next visit so the patient understands they will be financially responsible.
- Review your billing system defaults. If the AT modifier is auto-applied to every CMT claim, override the default and make the modifier a manual, per-visit decision tied to the note.
What Happens During a Medicare Chiropractic Audit
Medicare chiropractic audits come through several channels: RAC (Recovery Audit Contractor) reviews, SMRC (Supplemental Medical Review Contractor) targeted reviews, CERT (Comprehensive Error Rate Testing) sampling, and MAC (Medicare Administrative Contractor) prepayment reviews. Each requests documentation on a set of claims and compares the clinical notes against Medicare’s active treatment standard.
One question we hear constantly from practice managers is what happens if they fail the audit. The answer depends on the audit type, but the common outcome is a demand for repayment on every claim where the documentation did not support the AT modifier, plus extrapolation across similar claims if the error rate is high enough. For practices with years of reflexive AT modifier usage, the exposure can reach six figures.
The practices that survive audits intact are the ones whose notes were written to defend the modifier from the start: objective findings that change visit to visit, a treatment plan with measurable goals, and a documented transition when care shifts from active to maintenance.
In-House Documentation vs. a Billing Partner
The documentation problem behind the AT modifier is not a billing problem in the traditional sense. It is a workflow problem that starts in the treatment room and ends in the billing system. A billing partner with chiropractic experience can audit the documentation pattern, flag notes that would not survive a review, retrain staff on the active-versus-maintenance distinction, and configure the billing system so the AT modifier is a clinical decision rather than a default. These are the controls the OIG has repeatedly said CMS needs to implement, and they are the controls a specialized billing partner builds into the daily workflow.
Frequently Asked Questions
What is the AT modifier in chiropractic billing?
The AT modifier is appended to a chiropractic manipulative treatment claim to attest that the service was active or corrective treatment for subluxation, not maintenance care. Medicare requires it on every covered CMT claim. Without it, the claim is denied. With it but without supporting documentation, the claim is at risk on audit.
What is the Medicare chiropractic improper payment rate?
Chiropractic services carry a 33.6 percent improper payment rate according to the CMS CERT program, the highest among all Medicare Part B services. An OIG audit found that approximately 82 percent of Medicare chiropractic payments did not comply with requirements.
What triggers a Medicare chiropractic audit?
A high AT modifier rate relative to peers, high visit frequency per patient, repetitive documentation patterns, and claims volume above MAC-established thresholds are the primary triggers. RAC, SMRC, CERT, and MAC prepayment reviews all target chiropractic services.
Does Medicare cover maintenance chiropractic care?
No. Medicare covers manual spinal manipulation to correct a subluxation only when the treatment is active and corrective. Maintenance care, defined as treatment to maintain the current condition or prevent deterioration, is not covered regardless of whether the AT modifier is present.
What is the updated ABN form?
CMS released an updated Advance Beneficiary Notice form (CMS-R-131) in 2026 with a mandatory compliance deadline of May 12, 2026. The ABN is issued when a practice expects Medicare to deny a service, such as maintenance care, so the patient understands they will be financially responsible.
How far back can a Medicare chiropractic audit reach?
Audit lookback periods vary by audit type but commonly cover three to five years of claims. RAC reviews can request documentation on claims from prior years, and the exposure compounds if the same documentation pattern persists across the lookback period.
Next Steps
- Need the CPT code reference? See our chiropractic CPT codes guide for the CMT codes that carry the AT modifier.
- Pull your AT modifier rate and sample 20 to 30 charts this week. If the notes look the same visit to visit, that is the gap to fix before a contractor finds it.
- Ready to hand compliance off? Get matched with a chiropractic billing company that audits AT modifier documentation as part of the daily workflow.
Chiropractic has the highest Medicare improper payment rate in Part B, and the AT modifier is at the center of every audit. Whether you need a billing partner who audits your documentation before submission or want to compare your current billing company’s compliance controls, Chiropractor Billers connects you with vetted partners at no cost. More than 2,000 providers matched, all 50 states, over 15 years in medical billing, rates from 2.95 percent. Matching is 100 percent free.
