Claim adjustment reason code
Denial code CO-31 meaning
CARC 31, usually seen as CO-31: The payer cannot match the patient to a member on its records.
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- Reason code
- CARC 31
- Short name
- Patient not found as a member
- Plain meaning
- The payer cannot match the patient to a member on its records.
- Group codes
- CO-31: 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
- The member ID, name or date of birth on the claim does not match the payer's record.
- The claim went to the wrong payer.
What to check before resubmitting
- Check the ID card and run an eligibility check.
- Correct the patient information and resubmit.
Remark codes that often come with it
Related reason codes
Related pages
Questions
What does denial code CO-31 mean?
The payer cannot match the patient to a member on its records. This is Rivvi's plain-English summary of CARC 31. X12's exact wording is on x12.org.
How do I fix CO-31?
Check the ID card and run an eligibility check. Correct the patient information and resubmit.
Can I bill the patient for CO-31?
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 31?
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.