Medicare chiropractic claims: the AT modifier and what Medicare won't pay

What Medicare pays a chiropractor for

Medicare covers manual manipulation of the spine to correct a subluxation, billed with 98940 (one or two spinal regions), 98941 (three or four) or 98942 (five). That's all. Exams, X-rays, other treatments and manipulation outside the spine (98943) aren't covered when a chiropractor provides them, so they're the patient's cost.

AT means active treatment

Medicare pays for manipulation that's improving the patient's condition, not for maintenance once they've stopped improving. The AT modifier on 98940 to 98942 tells Medicare the treatment is active. A manipulation line without AT is treated as maintenance and denied.

When it's maintenance: GA or GZ

• GA: you expect Medicare to deny it as maintenance, and the patient signed an Advance Beneficiary Notice (ABN) before the visit. The patient can then be billed if Medicare denies it.
• GZ: you expect a denial and there's no signed ABN. The practice usually can't bill the patient.

What the note needs

Medicare looks for the subluxation and the regions treated, a treatment plan with goals, and progress toward them. When the notes stop showing improvement, care has become maintenance, whatever modifier is on the claim.

Check before you send

Summit Practice Billing stops a Medicare claim from a chiropractor that has anything other than 98940 to 98942, or a manipulation without AT, GA or GZ, before it goes out, with a reminder that other services are the patient's cost. Try your own codes in the free Claim Check.

Published October 29, 2026. Payer rules change, and Medicaid plans and insurers may differ from Medicare: check your payer's current policy before relying on any one rule here.