Glossary · Updated Aug 6, 2026
Assistant at Surgery Indicator
The assistant at surgery indicator is a per-procedure flag in the Medicare Physician Fee Schedule showing whether Medicare's payment restriction on assistants at surgery applies to that procedure. It answers "may this procedure ever support a separately paid assistant?"—not "will this claim pay?"
Indicator or modifier? Copy link
These are two different things, and mixing them up is the most common way this field gets misread. The indicator belongs to the procedure code: it is a field CMS publishes in the fee schedule file, describing Medicare's restriction for that procedure. The modifier belongs to the claim: it identifies who assisted and under what circumstance. You never submit the indicator on a claim—you look it up first to find out whether submitting modifier 80, 81, 82, or AS has any chance of being paid.
The four indicator values Copy link
All four values, in one table:
| Value | What it means |
|---|---|
| 0 | Restricted. Medicare may pay only if supporting documentation establishes that an assistant was medically necessary. |
| 1 | A statutory payment restriction applies. Medicare may not pay an assistant at surgery for this procedure. |
| 2 | The restriction does not apply. Medicare may pay an eligible assistant, subject to the other claim requirements. |
| 9 | The assistant at surgery concept does not apply. |
Value 2 is permission to try, not an approval Copy link
Indicator 2 is the least restrictive value, not a payment guarantee. It clears one gate—the procedure-level restriction—and leaves every other gate standing: whether the assistant is a practitioner type Medicare recognizes, whether the assistant was medically necessary for this case, whether the operative report supports it, whether the practitioner is enrolled, and whether the surgery happened at a teaching hospital with a resident available. Indicator 1 is labelled statutory for a concrete reason: federal law itself bars payment for an assistant at surgery on a procedure where, on the most recent data, a physician assists in fewer than five percent of cases nationally. A second statutory restriction is narrower and easy to miss—an assistant at surgery in a cataract operation is excluded unless a quality improvement organization or the Medicare contractor approved the assistant in advance, based on a complicating medical condition. All four values describe Original Medicare only—commercial and Medicaid plans set their own assistant-at-surgery policies and are not bound by this field.
Four modifiers, two Medicare rates Copy link
CMS recognizes four assistant-at-surgery modifiers, which fall into two payment tiers:
| Modifier | Who or what it identifies | Medicare rate |
|---|---|---|
| 80 | Physician serving as assistant surgeon | 16% |
| 81 | Physician serving as minimum assistant surgeon—a lesser level of assistance than 80 | 16% |
| 82 | Physician serving as assistant surgeon because no qualified resident was available | 16% |
| AS | Physician assistant (PA), nurse practitioner (NP), or clinical nurse specialist (CNS) assisting at surgery | 13.6% |
Watch the wording on 80, 81, and 82 Copy link
Modifiers 80, 81, and 82 all identify a physician who assisted. "Physician assistant" as a job title is the other tier entirely: a PA—along with an NP or CNS—bills assistant-at-surgery services with modifier AS, not with 80, 81, or 82. The 13.6% figure is 85% of the physician's 16%, which is the standard Medicare reduction for services these practitioners bill under their own identity. Both percentages apply to the procedure's surgical fee schedule amount, and neither is the final remittance—locality adjustment, sequestration, patient responsibility, and multiple-procedure reductions all land afterward.
What the operative report has to show Copy link
Documentation matters even when the indicator is 2. The operative report should describe what the assistant actually did and why skills beyond those of ancillary operating-room staff were needed; naming the assistant in the report header is not enough on its own. Medicare's standard for a PA, NP, or CNS is that the practitioner actively assisted in performing the procedure and furnished more than merely ancillary services. When the indicator is 0, the documentation must additionally establish that an assistant was medically necessary for that case, and contractors generally expect it up front rather than on appeal.
Teaching hospitals restrict this further Copy link
Medicare generally does not pay an assistant at surgery at a teaching hospital that both runs a residency program in the specialty the surgery requires and has a qualified resident available to assist. The regulation lists five conditions that restore payment. Four are operational: exceptional medical circumstances, complex procedures needing a team of physicians each performing a discrete function, concurrent care by a physician of another specialty, and a primary surgeon who has an across-the-board policy of never involving residents in patient care. The fifth is a carve-out rather than an exception—it covers services not tied to a procedure that falls under the five-percent rule to begin with. Modifier 82 is how a physician's assistant-at-surgery claim signals that no qualified resident was available; a PA, NP, or CNS still bills AS rather than switching to 82, and the same teaching-hospital restriction applies to them.
Where to see it applied Copy link
Every code page shows this code's assistant at surgery indicator in its billing-policy panel, and—when the indicator permits it—computed -80/81/82 and -AS amounts in the modifier amounts section. CPT 27447 (total knee replacement) carries indicator 2, so its two modifier amounts show the 16% and 13.6% tiers side by side.
Frequently asked Copy link
Does indicator 2 mean an assistant surgeon claim will be paid?
No. Indicator 2 means Medicare's procedure-level restriction does not apply. The claim still has to clear practitioner eligibility, medical necessity, documentation, Medicare enrollment, and—at a teaching hospital—the qualified-resident rule. For other payers, credentialing, network participation, and prior authorization can cause a denial regardless of what this field says.
Can any surgery bill an assistant surgeon?
No. Only procedures with indicator 2, or indicator 0 with documentation establishing medical necessity, can support a separately paid assistant at surgery under Medicare. Indicator 1 procedures cannot, and indicator 9 means the concept does not apply to that code at all.
What is the difference between modifiers 80, 81, 82, and AS?
Modifiers 80, 81, and 82 identify a physician who assisted: 80 for assistant surgeon, 81 for minimum assistant surgeon, and 82 when no qualified resident was available at a teaching hospital. All three pay 16% of the procedure's surgical fee schedule amount. Modifier AS identifies a PA, NP, or CNS assisting at surgery, and pays 13.6%—85% of the physician amount.
Do I bill modifier AS by itself, or with 80, 81, or 82?
For Medicare, by itself. CMS instructs that only the AS modifier be reported when a PA, NP, or CNS bills an assistant-at-surgery service, and contractors treat 80, 81, and 82 as physician-only modifiers a non-physician practitioner should not append. Some commercial and Medicare Advantage plans require the opposite—AS paired with 80, 81, or 82—and reject a claim carrying AS alone, so check that payer's own policy before dropping the companion modifier.
Can a surgical first assistant or surgical technologist bill Medicare with modifier AS?
Modifier AS is Medicare's assistant-at-surgery modifier for a PA, NP, or CNS. A certification such as CSFA, CST, or RNFA does not by itself make someone one of those three practitioner types, and having an NPI is not the same as being an eligible one—Medicare contractors state outright, for example, that a registered nurse first assistant is not a recognized provider for this service. Commercial and Medicaid plans set their own eligibility rules, so check the specific payer's policy for non-Medicare claims.
Whose NPI goes on a PA, NP, or CNS assistant-at-surgery claim?
Their own. Medicare requires PAs, NPs, and CNSs to have their own non-physician practitioner NPI for billing purposes, and to be enrolled. Modifier AS is not a way to report an uncredentialed practitioner's work under the surgeon's identity.
Is an assistant at surgery the same as a co-surgeon?
No. An assistant supports the primary surgeon through the procedure. A co-surgeon performs a distinct part of the operation and reports modifier 62 when Medicare's requirements are met. CMS states directly that surgeons billing as co-surgeons, or as a surgical team under modifier 66, are not acting as assistants at surgery, and it does not generally pay an assistant on top of a paid co-surgeon or team claim.
Why was modifier AS denied on a procedure with indicator 2?
Common causes are the assistant not being a PA, NP, or CNS enrolled with Medicare; an operative report that names the assistant without describing what they did; a teaching hospital where a qualified resident was available; or a non-Medicare payer applying its own assistant-at-surgery policy. Indicator 2 rules out only one reason for denial.
Sources Copy link
- CMS Medicare Physician Fee Schedule Relative Value Files
- CMS Medicare Claims Processing Manual (Pub. 100-04)
- 42 USC 1395w-4(i)(2) (SSA §1848(i)(2))—Assistants-at-surgery
- 42 USC 1395y(a)(15) (SSA §1862(a)(15))—exclusion of assistant-at-surgery services
- 42 CFR 415.190—Conditions of payment: assistants at surgery in teaching hospitals
Written from primary CMS sources—see how we source, compute, and verify everything on this site.
- Medicare recognizes four assistant-at-surgery modifiers: 80, 81 and 82 for a physician, and AS for a physician assistant, nurse practitioner, or clinical nurse specialist. —CMS Medicare Claims Processing Manual (Pub. 100-04)
- Medicare pays a physician's assistant-at-surgery service at 16 percent of the amount otherwise applicable for the surgical payment. —CMS Medicare Claims Processing Manual (Pub. 100-04)
- A PA, NP, or CNS assistant-at-surgery service is paid at 85 percent of the physician amount, i.e. 13.6 percent of the surgical fee schedule amount. —CMS Medicare Claims Processing Manual (Pub. 100-04)
- Medicare contractors may not pay assistants at surgery for procedures in which a physician is used as an assistant at surgery in fewer than five percent of cases nationally. —CMS Medicare Claims Processing Manual (Pub. 100-04)
- The five-percent restriction is statutory: where the national average use of a physician as an assistant at surgery for a procedure is less than 5 percent, no payment may be made for an assistant at surgery on that procedure. —42 USC 1395w-4(i)(2) (SSA §1848(i)(2))—Assistants-at-surgery
- Federal law caps a physician's assistant-at-surgery fee schedule amount at 16 percent of the amount otherwise determined for the global surgical service. —42 USC 1395w-4(i)(2) (SSA §1848(i)(2))—Assistants-at-surgery
- An assistant at surgery in a cataract operation is excluded from Medicare payment unless a quality improvement organization or the Medicare contractor approved the use of an assistant before the surgery, based on a complicating medical condition. —42 USC 1395y(a)(15) (SSA §1862(a)(15))—exclusion of assistant-at-surgery services
- A PA, NP, or CNS assistant-at-surgery service is payable only when the practitioner actively assists the physician in performing the procedure and furnishes more than just ancillary services. —CMS Medicare Claims Processing Manual (Pub. 100-04)
- PAs, NPs, and CNSs must have their own non-physician practitioner NPI for billing purposes. —CMS Medicare Claims Processing Manual (Pub. 100-04)
- Only the AS modifier is reported when a PA, NP, or CNS bills an assistant-at-surgery service to Medicare; 80, 81, and 82 are physician-only modifiers. —CMS Medicare Claims Processing Manual (Pub. 100-04)
- Fee schedule payment is not available for an assistant at surgery at a hospital that has a training program in the specialty required for the procedure and a resident available to assist, except in five defined circumstances. —42 CFR 415.190—Conditions of payment: assistants at surgery in teaching hospitals
- When two or more surgeons are required for their individual skills and bill as co-surgeons (modifier 62) or a surgical team (modifier 66), the additional physicians are not acting as assistants at surgery, and Medicare does not generally allow an assistant surgeon in addition. —CMS Medicare Claims Processing Manual (Pub. 100-04)
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