Modifier -23 (Unusual Anesthesia) is used on anesthesia service CPT codes when a procedure that normally requires no anesthesia or only local anesthesia must be performed under general anesthesia because of unusual patient or procedural circumstances. It applies only to anesthesia CPT codes (00100–01999) and must be sequenced after the anesthesia performance/direction modifier (for example AA, QK, QZ).

Although modifier -23 documents the need for general anesthesia in an atypical situation, it is considered informational-only and does not by itself increase reimbursement. Payers such as Medicare MACs and major commercial carriers treat the modifier as explanatory; claims should include supporting clinical documentation that justifies why general anesthesia was required. Some payers may request additional narrative or documentation during audit or review.

Use modifier -23 when unforeseen or unusual circumstances require general anesthesia for a procedure that ordinarily would use no or only local anesthesia (for example, an IUD removal performed under general anesthesia due to extreme patient anxiety). Report the appropriate anesthesia CPT code with the performance/direction modifier first (e.g., AA or QZ) and place modifier -23 in the second position. Include pertinent diagnostic codes and clinical notes to substantiate medical necessity. Remember that adding modifier -23 documents the situation but does not automatically trigger extra payment; reimbursement remains subject to standard payer rules and reasonable charge determination.