CO-31 Denial Code: Payer can't match the patient to an active policy
The payer can't match the patient to an active policy - usually a wrong member ID, name, or date of birth, or the patient isn't covered by this payer. Verify identity/eligibility and correct or rebill.
- Group code
- CO - Contractual Obligation
- Code type
- CARC
- Billable to patient?
- Usually a data fix; patient responsibility only if billed as PR-31
- Appealable?
- Usually a data fix; appeal only if coverage is confirmed
- Category
- Coverage & Benefits
- Common pairing
- N382
CAS*CO*31*125.00On a paper EOB it shows as CO-31.What CO-31 means
CO-31 means the payer searched its membership and could not find the patient as an insured. Most often the member ID, name spelling, or date of birth on the claim does not match the payer's records; sometimes the patient genuinely isn't covered by this payer. Re-verify identity and eligibility, correct the demographics, and resubmit - or bill the correct payer. Some payers issue code 31 as PR-31 (patient responsibility) rather than CO.
Common causes
- The member ID, name, or date of birth doesn't match the payer's records.
- A typo or an outdated card created an identity mismatch.
- The patient isn't covered by this payer (the wrong plan was billed).
- Coverage had not started, or had ended, for the date of service.
How to fix it
- Re-verify the patient's exact name, DOB, and member ID against the card and a real-time eligibility check.
- Correct the demographic/ID data and resubmit a corrected claim.
- If a different payer covers the patient, rebill the correct payer.
- If eligibility confirms coverage and the data was correct, appeal with the verification.
How to prevent it
- Capture and verify insurance details at registration with real-time eligibility.
- Scan the insurance card and confirm name, DOB, and ID match exactly.
- Re-verify identity for returning patients whose coverage may have changed.
Appeal letter template
Fill in the bracketed fields, attach your supporting documentation, and send through the payer's appeal channel. This is a starting point — adjust to your payer's requirements.
Re: Member Identification (CO-31) - Claim [Claim Number] Patient: [Patient Name] | DOB: [DOB] | Member ID: [Member ID] Date(s) of Service: [DOS] To Whom It May Concern: Claim [Claim Number] was denied under CO-31 (patient not identified as insured). Our eligibility verification on [Verification Date] (reference [Ref Number]) confirms the patient was active under member ID [Member ID] for the date(s) of service, with matching name and date of birth. Verification is enclosed. We request reprocessing of this claim. Sincerely, [Your Name], [Practice Name] | [Phone] | [NPI/TIN]