CO-31: Patient Not Identified as Insured

What Does CO-31 Mean?

CO-31 designates the denial as the provider's contractual responsibility. The payer is saying the claim cannot be processed because the submitted patient identifiers do not match any enrollment record, and the provider must correct and resubmit. Since this is an information-quality issue on the provider's side, the patient cannot be billed for the denied amount. This is the standard pairing for CARC 31 — it appears on the vast majority of these denials.

When CARC 31 appears on a remittance, the payer searched its enrollment database using the identifiers on your claim and found no match. The patient could not be linked to any active policy. This does not necessarily mean the patient is uninsured — it means the information you submitted does not align with what the payer has on file.

The most frequent trigger is a data entry error at registration: a transposed digit in the member ID, a misspelled last name, a date of birth keyed incorrectly, or a subscriber ID confused with the group number. Less commonly, CARC 31 appears when the claim was routed to the wrong payer entirely — the patient changed jobs and insurance, but your system still shows the old carrier. It can also surface when the patient's enrollment has not yet been loaded into the payer's system, particularly with new-year plan changes or employer group transitions.

Under Group Code CO, this denial is the provider's responsibility to resolve. You cannot bill the patient for a CO-31 adjustment because the payer did not reject the service — they simply could not identify who the patient is. The fix is straightforward: verify the correct insurance details, update your records, and resubmit a clean claim. This is one of the most preventable denial codes, and high-volume practices that implement real-time eligibility checks at scheduling and check-in can virtually eliminate it.

Common Causes

How to Resolve

Verify the patient's insurance identifiers against the payer's records, correct any mismatches, and resubmit the claim.

1. Verify insurance identifiers Cross-reference the claim's member ID, subscriber name, date of birth, and group number against the patient's physical or scanned insurance card. Run a 270/271 eligibility check to confirm active enrollment.
2. Correct the mismatch Update the patient's record in your PM system with the verified identifiers. Common fixes include correcting transposed member ID digits, updating a name change, or switching to the correct payer.
3. Resubmit the claim File a corrected claim with the updated patient and insurance information. Monitor for acceptance confirmation from the clearinghouse to verify the resubmission was received.
4. Contact the patient if coverage is not found If the eligibility check confirms no active coverage with any payer you have on file, contact the patient to obtain current insurance details or discuss self-pay arrangements.

Common RARC Pairings

The RARC code tells you exactly what triggered the CO-31:

How to Prevent CO-31

• Run real-time eligibility verification at scheduling and again at check-in to catch enrollment mismatches before the claim is ever submitted
• Scan or photograph the insurance card at every visit and compare it against your system records — do not rely on data from previous visits
• Implement front-desk validation workflows that require confirmation of member ID, group number, and subscriber name before the encounter proceeds
• Use automated patient intake systems that cross-reference submitted insurance data against payer eligibility files in real time

General Prevention

• Run electronic eligibility verification (270/271) for every patient at scheduling and again at check-in to catch coverage issues before service delivery
• Scan or photograph both sides of the patient's insurance card at every visit and compare against the information in your system
• Implement front-desk workflows that require staff to verify the member ID, group number, and subscriber information match exactly before the encounter
• Use automated patient intake tools that cross-reference submitted insurance data against payer eligibility files in real time
• Flag patients with recently changed employers, new plan enrollments, or coverage changes from the prior visit for mandatory re-verification
• Train registration staff to recognize common data entry errors — transposed digits, first/last name reversal, and outdated policy numbers

Also Filed As

The same CARC 31 may appear with different Group Codes:

Related Denial Codes