Non-physician practitioners (NPPs)’ participation in surgical or perioperative care is not limited to low and middle-income countries, as suggested by a decade-old healthcare workforce research published by the National Institutes of Health.
Today, even in the USA, NPPs function as integral members of the surgical care team in hospitals and outpatient clinics. However, when a nurse practitioner (NP), physician assistant (PA), or clinical nurse specialist (CNS) assists the primary surgeon during an operative procedure, the billing requirements change.
Primarily, the billing should indicate that an NPP provided care services, and the modifier AS makes that distinction.
Modifier AS – Description
Modifier AS is an HCPCS Level II modifier, and without it, the claim for a surgery involving NPP assistance is either wrongly reimbursed or rejected completely.
Hence, understanding modifier AS is the most effective approach to safeguard your revenue on assistant-at-surgery claims. Here is how the modifier is described as per the Centers of Medicare & Medicaid Services (CMS)’s Medicare Claims Processing Manual.
“Physician assistant, nurse practitioner, or clinical nurse specialist services for assistant at surgery.”
Understanding the AS Modifier
It is important to remember that modifier AS is an HCPCS modifier and is not a CPT modifier (although they function similarly). CMS established this modifier to distinguish assistant-at-surgery services performed by non-physician practitioners from those performed by physicians.
Assistant-at-surgery claims may also involve modifiers 80, 81, or 82, depending on payer policy and claim requirements. Noridian Healthcare Solutions (CMS Medicare Administrative Contractor, Jurisdiction E) explains that this modifier is reported with appropriate procedure codes for cases where a CNS, NP, or PA assists a principal surgeon as a surgical assistant. Additionally, the assistant surgeon’s role must extend beyond ancillary services.
Modifier AS-eligible procedures may vary based on the assistant-at-surgery policy. Additionally, the claim is payable if the assistant at surgery is qualified and allowed to provide services for that specific procedure.
Typically, surgical assistants, also known as first assistants, handle tasks like exposing the surgical site, closing incisions, and suturing to help the primary operating surgeon.
Scenarios Where Modifier AS is Applicable
The following are three scenarios where the AS modifier applies:
Abdominal Surgery Requiring a PA Assistant
Consider the case of a 42-year-old male patient who undergoes a laparoscopic colectomy (CPT code 44204). For this procedure, the CMS assistant-at-surgery status indicator is 2. This indicates that an assistant at surgery will be paid.
A physician assistant actively assists the attending colorectal surgeon throughout the operation. Therefore, the claim is submitted for colectomy CPT code 44204, with modifier AS. And as per payer requirements, the operative notes highlight the PA’s active role throughout the procedure.
NP-Assisted Cardiac Surgery
Imagine an NP actively assisting a cardiothoracic surgeon during a coronary artery bypass graft (CABG), CPT code 33510, for a 50-year-old male patient. The procedure carries an assistant-at-surgery status indicator 2.
Following the procedure, the billing team reports modifier AS to the CPT code to explain the NP’s active assistance during surgery. Moreover, the NP’s participation as the primary bedside assistant to the cardiac surgeon throughout the operation is documented and submitted with the claim form.
CNS-Assisted Total Hip Arthroplasty
Consider the case of a 72-year-old patient with severe osteoarthritis of the right hip. The patient undergoes a total hip arthroplasty. For the hip replacement procedure (CPT code 27130), CMS assistant-at-surgery indicator 2 applies. Why is this important? A CNS with prior orthopedic surgical experience actively assists till the end of the procedure.
She participates during the exposure, retraction, and wound closure. Hence, during billing, the biller appends modifier AS to the total hip arthroplasty CPT code.
Modifier AS – Billing Guidelines
The following essential billing guidelines apply to the AS modifier for accurate billing:
Never Bill the Modifier for Physicians
Modifier AS applies only to non-physician practitioners, and FCSO Medicare explains that if it is appended when a physician (MD or DO) acted as an assistant at surgery, the claims will be denied.
Submit the Claim with Complete Documentation
The medical necessity of an assistant surgeon’s services should be justified by attaching detailed supporting documentation with the claim. Therefore, the submitted documentation should include the following:
- Clinical condition of the patient.
- Details of procedures or services performed.
- An operative note documenting the assistant surgeon’s active role during the procedure, not merely their presence.
- An explanation why an NPP was appointed as part of the surgical team, e.g., “a resident surgeon was unavailable”.
Review Assistant-at-Surgery Indicator
The payment details for an assistant at surgery are published by the Medicare Physician Fee Schedule Database (MPFSDB). According to Medicare FCSO, the indicator value applicable to every CPT code for an assistant-at-surgery claim should be confirmed before claim submission.
Procedures assigned indicator 1 are generally not eligible for assistant-at-surgery reimbursement. The following table provides a comprehensive breakdown of indicators and their relevant billing actions.
| Indicator | What It Means | Billing Action |
|---|---|---|
| 0 | Payment restriction applies unless supporting documentation justifies it. | Submit supporting operative documentation to establish medical necessity for payment. |
| 1 | Statutory payment restriction applies to assistants at surgery. | Do not bill assistant-at-surgery services to avoid claim rejection. |
| 2 | Assistant at surgery will be paid with the proper modifier. | Use an assistant-at-surgery modifier (80, 81, 82, or AS) for just reimbursement. |
| 9 | The assistant-at-surgery concept does not apply. | Do not bill assistant-at-surgery services for these procedures. |
Verify State Scope-of-Practice Eligibility
The Medicare Carriers Manual explains that CNS, PA, or other professionals must be eligible to provide assistant-at-surgery services in line with the state laws. Since January 1, 1998, there have been no restrictions on the service setting, but state scope-of-practice authorization must be confirmed before billing.
Check Payer-Specific Details
Reimbursement for assistant-at-surgery services varies by payer and provider type. So, commercial payers’ rates will differ from those of Medicare. However, generally, commercial payers reimburse claims with modifier AS at 10% of the allowed amount for the surgery. While Medicare Advantage reimburses at 13.6% and Medicaid at 16% of the established fee.
Therefore, billers should verify payer-specific reimbursement rules before claim submission. We recommend that billers check the PFS Lookup Tool for the latest Medicare Administrative Contractor (MAC) rates.
Reduce Modifier AS Denials with MediBillMD
Modifier AS is a commonly misunderstood modifier. It is used to explain assistant-at-surgery services. If a PA, NP, or CNS assisted the primary surgeon throughout the surgery, the AS modifier must be appended to ensure a clean billing process and to protect revenue that might otherwise be written off.
If your in-house teams are unable to handle surgical billing, we recommend opting for professional medical billing services from renowned companies like MediBillMD. Certified coders and billers at MediBillMD can identify modifier usage issues before claim submission to help ensure claims are:
- Accurate
- Timely
- Defensible under payer review
