Background History of the AT Modifier

The Active Treatment ( AT) modifier was developed to clearly define the difference between active care and maintenance care.

In 2018, the Comprehensive Error Rate Testing Program found a high error rate (41%) in chiropractic claims, mostly due to poor or missing documentation. To reduce errors, CMS clarified rules around the AT modifier.

What the AT Modifier Means:

• Required on claims for CPT codes 98940–98942 (spinal manipulation) since October 1, 2004.
• Used only for active/corrective treatment (acute or chronic conditions).
• Not used for maintenance therapy (ongoing supportive care without expected improvement).

Types of Treatment Covered:

• Acute subluxation: New injury, expected improvement with treatment.
• Chronic subluxation: Long-term condition, therapy may help function but not fully resolve.
• Once a condition stabilizes without further improvement, care becomes maintenance therapy → not covered by Medicare.

Maintenance Therapy:

• Focuses on preventing disease, promoting health, or maintaining a chronic condition.
• Medicare does not cover maintenance therapy.
• Providers should consider an Advance Beneficiary Notice (ABN) so patients know they may be responsible for payment.

Key Rule: If a claim for 98940–98942 does not include the AT modifier when active treatment is provided, Medicare will deny the claim.