Modifier AT (active treatment) defines the difference between active treatment and maintenance treatment.

The AT modifier is required under Medicare billing to receive reimbursement for CPT codes 98940-98942. For Medicare purposes, the AT modifier is used only when chiropractors bill for active / corrective treatment (acute and chronic care).

Every chiropractic claim for 98940 / 98941 / 98942, should include the AT modifier if active / corrective treatment is being performed. Claims that do not contain modifier AT will deny.

Do not use modifier AT for maintenance therapy. 
 

Reference

• MLN Matters Special Edition, SE1602 - Use of the AT modifier for Chiropractic Billing (new information along with information in MM3449)