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 or corrective treatment (acute and chronic care).

Every chiropractic claim for 98940, 98941 and 98942, should include the AT modifier if active or 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)