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CO-261 Denial Code: Inconsistent with Patient History

CO-261 means the procedure or service is inconsistent with the patient's history. Based on its claims history, the payer believes the service could not have been performed as billed, for example a procedure on an organ already removed or a one-time service that was already paid.

Quick facts

Code
CO-261 (CARC 261)
Status
Active In use since June 1, 2014.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The provider is responsible for resolving the inconsistency. The amount generally cannot be billed to the patient.
Official description
The procedure or service is inconsistent with the patient's history.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-261 means

CARC 261 says the procedure or service is inconsistent with the patient’s history. The payer checked the claim against what it knows about the patient, usually from its own claims history, and found a contradiction.

This differs from age or sex edits, which compare the code with demographic data. CO-261 compares it with past events. Examples include a procedure on a body part that history shows was removed, a service limited to once per lifetime that was already paid, or a subsequent procedure with no initial procedure in history.

Common causes

  • Laterality error: the claim reports the wrong side, so it looks like a repeat of an earlier procedure. Check modifiers RT, LT, and 50 in box 24D.
  • Wrong code for an initial versus subsequent service.
  • Once-in-a-lifetime service billed again, either in error or because it was genuinely repeated for a documented reason.
  • Incomplete payer history, because an earlier procedure was billed to a different plan or not billed at all.
  • Wrong patient on the claim or a merged record.

How to fix it

  1. Ask the payer what history conflicts with the claim, including the date and code of the prior service.
  2. Review the medical record for the current and prior services.
  3. If the claim was wrong (side, code, or patient), submit a corrected claim with frequency code 7.
  4. If the claim was right but history is incomplete, send records showing the actual history, such as the earlier procedure being done by a different payer, or a revision or re-implant being clinically necessary.
  5. If a limit applies and the service was repeated for a valid reason, check whether the payer’s policy allows an exception and appeal with documentation.
  6. Do not bill the patient under the CO group.

How to prevent it

  • Ask about prior surgeries and relevant history at intake and record them clearly.
  • Require laterality modifiers wherever the code’s side matters.
  • Know which services your payers limit to once per lifetime or once per side.
  • Use pre-submission edits that check repeated procedures against prior claims; a Claims Validator can flag suspicious repeats.
  • See preventable causes of medical claim denials for similar data-consistency issues.

Remark codes that may appear with CO-261

  • N214 (Missing/incomplete/invalid history of the related initial surgical procedure(s).): The history of the related initial surgical procedure is missing, incomplete, or invalid.
  • M86 (Service denied because payment already made for same/similar procedure within set time frame.): Payment was already made for the same or similar procedure within a set time frame.
  • N537 (We have examined claims history and no records of the services have been found.): The payer examined claims history and found no record of the related services.
  • CO-6 (The procedure/revenue code is inconsistent with the patient's age.): The procedure is inconsistent with the patient's age.
  • CO-7 (The procedure/revenue code is inconsistent with the patient's gender.): The procedure is inconsistent with the patient's sex.
  • CO-11 (The diagnosis is inconsistent with the procedure.): The diagnosis is inconsistent with the procedure.
  • CO-B13 (Previously paid.): Payment for the service may have been made in a previous payment.

CO-261 FAQ

What are examples of CO-261?

Billing a procedure on an organ the payer's history shows was removed, billing a once-per-lifetime service a second time, or billing a follow-up procedure when no initial procedure appears in history.

What if the patient's history at the payer is wrong?

Payer history can be wrong or incomplete, for example when an earlier service was billed to another plan. Send records showing the correct history and ask for reprocessing.

Should I correct the claim or appeal?

If the claim had an error, such as the wrong side, wrong code, or wrong patient, submit a corrected claim. If the claim was right and the payer's history is wrong or incomplete, appeal with documentation.