Modifier

A two-character code appended to a CPT code to indicate that a service was altered in some way without changing its definition. In behavioral health, the most critical modifiers are: -25 (significant, separately identifiable E/M on the same day as another procedure — required when billing same-day E/M + psychotherapy); -59 (distinct procedural service, used to override bundling edits); -GT (synchronous telecommunication, used for telehealth on some payers); and place-of-service modifiers 95/GT. Missing or incorrect modifiers are the #1 cause of CO-4 and CO-97 denials.