Claim adjustment reason code
Denial code CO-231 meaning
CARC 231, usually seen as CO-231: The two procedures cannot reasonably be done on the same day or in the same session.
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- Reason code
- CARC 231
- Short name
- Mutually exclusive procedures
- Plain meaning
- The two procedures cannot reasonably be done on the same day or in the same session.
- Group codes
- CO-231: Contractual obligation. The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Plain-English summary written by Rivvi. X12 owns the CARC list and its exact wording, which is not reproduced here. Read it on the X12 CARC list (list dated November 1, 2025, checked October 23, 2026). This page does not decide how a claim is paid.
Common causes
- An NCCI mutually exclusive edit pairs this code with another one billed.
What to check before resubmitting
- Check the NCCI edit and whether a modifier is allowed.
- Bill only the procedure documented, or add a supported modifier.
Related reason codes
Related pages
Questions
What does denial code CO-231 mean?
The two procedures cannot reasonably be done on the same day or in the same session. This is Rivvi's plain-English summary of CARC 231. X12's exact wording is on x12.org.
How do I fix CO-231?
Check the NCCI edit and whether a modifier is allowed. Bill only the procedure documented, or add a supported modifier.
Can I bill the patient for CO-231?
With group code CO, no. CO means the provider absorbs the amount under its contract or the payer's rules.
Which group codes come with CARC 231?
Most often CO (contractual obligation). The group code, not the reason code, says who owes the amount.
What is the difference between a CARC and a RARC?
A claim adjustment reason code (CARC) says why a claim line was paid differently than billed. A remittance advice remark code (RARC) adds detail, such as which field is missing.