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CO-54 Denial Code: Assistant or Extra Surgeon Not Covered

CO-54 means the payer determined that multiple physicians or assistants aren't covered for this procedure or case. Typically an assistant surgeon, co-surgeon, or team surgery claim was billed for a service where the payer doesn't allow one.

Quick facts

Code
CO-54 (CARC 54)
Status
Active In use since January 1, 1995; last modified July 1, 2017.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The usual group. The provider absorbs the amount and can't bill the patient unless the payer allows it under an advance notice.
Official description
Multiple physicians/assistants are not covered in this case. Usage: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-54 means

CARC 54 says multiple physicians or assistants are not covered in this case. Surgical and procedural claims may include more than one provider: a primary surgeon, an assistant (physician or non-physician), co-surgeons each performing distinct parts of a procedure, or a surgical team. Payers decide for each procedure whether these extra roles are payable. When they’re not, the additional provider’s claim is denied with CO-54.

The usage note points to the 835 Healthcare Policy Identification segment for the payer’s policy.

For Medicare, the physician fee schedule assigns indicators that say whether a procedure can have an assistant at surgery, co-surgeons, or a team. Many commercial payers use the same indicators or similar lists.

Common causes

  • Assistant billed on a procedure where assistants aren’t payable under the fee schedule indicator or payer policy.
  • Co-surgeon modifier 62 on a code that doesn’t allow co-surgeons, or used when only one surgeon performed the key parts.
  • Team surgery modifier 66 without supporting documentation or on a code that doesn’t allow it.
  • Wrong modifier, such as 80 for a non-physician assistant when the payer wants AS.
  • Both surgeons billing as primary without co-surgery modifiers.
  • Teaching hospital rules limiting assistant billing when a qualified resident was available.

How to fix it

  1. Check the procedure’s surgery indicators and payer policy for assistants, co-surgeons, and teams.
  2. Review the operative report to confirm each provider’s role.
  3. Correct modifiers in box 24D (80, 81, 82, AS, 62, 66) and send a corrected claim with resubmission code 7 in box 22.
  4. Appeal with documentation if the payer allows exceptions when medical necessity for an additional surgeon is documented.
  5. Write off if the procedure doesn’t allow the role billed.

How to prevent it

  • Verify assistant and co-surgeon eligibility before scheduling procedures with more than one surgeon.
  • Document each surgeon’s role clearly in the operative report.
  • Coordinate billing between surgeons so modifiers match.
  • Scrub surgical claims for modifier and indicator conflicts. A Claims Validator can flag assistant modifiers on codes that don’t allow them.

Remark codes that may appear with CO-54

  • N646 (Reimbursement has been adjusted based on the guidelines for an assistant.): Reimbursement was adjusted based on the payer's guidelines for an assistant.
  • N249 (Missing/incomplete/invalid assistant surgeon primary identifier.): The assistant surgeon's identifier is missing or invalid.
  • CO-59 (Processed based on multiple or concurrent procedure rules. (For example multiple surgery or diagnostic imaging, concurrent anesthesia.)): Reduction under multiple or concurrent procedure rules, which may appear on the same surgical claim.
  • CO-B20 (Procedure/service was partially or fully furnished by another provider.): The procedure was partially or fully furnished by another provider.
  • CO-97 (The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.): Bundled into another procedure's payment.
  • CO-194 (Anesthesia performed by the operating physician, the assistant surgeon or the attending physician.): Anesthesia performed by the operating or assistant surgeon.

CO-54 FAQ

How do I know if a procedure allows an assistant surgeon?

For Medicare, the physician fee schedule has indicators for assistant at surgery, co-surgeons, and team surgery for each code. Commercial payers often follow those indicators or publish their own lists.

Which modifiers apply to assistants and co-surgeons?

Common modifiers include 80, 81, and 82 for assistant surgeons, AS for non-physician assistants at surgery, 62 for co-surgeons, and 66 for team surgery. Payers set which are accepted for each code.

Can I appeal CO-54?

Yes, if the payer allows an assistant or co-surgeon when medical necessity is documented. Send the operative report showing why an additional surgeon was needed.

Does CO-54 affect the primary surgeon's payment?

Usually not. CO-54 normally appears on the additional provider's claim or line. The primary surgeon's claim is processed on its own, although it may carry other adjustments such as multiple procedure reductions.