Question: When a physician assistant (PA) assists in surgery on an outpatient basis, does this fit the incident-to definition? When billing incident-to, should I use the surgeon's information at all on the claim? Utah Subscriber Answer: A PA can bill for assisting in surgery under Medicare by appending HCPCS modifier -AS (Physician assistant, nurse practitioner, or clinical nurse specialist services for assistant at surgery) to the CPT code, provided the procedure is billable under Medicare's guidelines. If a physician assists in surgery, he or she reports the same CPT code that the surgeon uses and adds -80 (Assistant surgeon) or -81 (Minimum assistant surgeon). Some non-Medicare payers may not know that a PA can assist in surgery and therefore may not recognize a claim for PA surgical assistance. You may need to educate private payers on the Medicare guidelines for this.