Eligibility

Denial code CO-31: Patient cannot be identified as our insured

The payer cannot match the patient on the claim to any member in its system.

Reason code

CARC 31

Typical group code

What CO-31 actually means

The identifying data on the claim — member ID, name, date of birth — did not match a member record at this payer. Either the demographics are wrong, or the patient is insured somewhere else entirely. It is a data-matching failure rather than a coverage decision, which is good news: the underlying claim is usually payable once the identity resolves.

Why this denial happens

The member ID was mistyped or is missing a required alpha prefix.
The patient’s name on the claim differs from the name on the policy (maiden name, hyphenation, suffix).
The claim went to the wrong payer or the wrong plan within a payer family.
The patient is covered as a dependent and was submitted as the subscriber.

How to resolve a CO-31 denial

Re-run eligibility with the member ID exactly as printed on the card, prefix included.
Confirm the legal name and DOB the payer has on file and match the claim to it.
Verify the correct payer ID — large payer families route by plan, and the wrong ID lands at a plan that has never heard of the member.
Correct and resubmit once the record matches.

How to prevent it

Scan or photograph insurance cards at registration instead of transcribing them.
Run electronic eligibility at check-in; a failed eligibility response predicts this denial exactly.

Frequently asked

What does denial code CO-31 mean?

The payer cannot match the patient on the claim to any member in its system. The X12 description reads: "Patient cannot be identified as our insured."

How do I fix a CO-31 denial?

Re-run eligibility with the member ID exactly as printed on the card, prefix included. Confirm the legal name and DOB the payer has on file and match the claim to it. Verify the correct payer ID — large payer families route by plan, and the wrong ID lands at a plan that has never heard of the member. Correct and resubmit once the record matches.

Can CO-31 be billed to the patient?

Generally no. The recommended path for this code is "appeal or correct and resubmit" — check your payer agreement before transferring any balance to the patient.

Related denial codes

CO-140 · Patient ID number and name do not match PR-26 · Expenses incurred prior to coverage PR-27 · Expenses incurred after coverage terminated CO-109 · Not covered by this payer — send to the correct payer

Related billing terms

Eligibility verification

See how much CO-31 is costing you

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General revenue-cycle guidance, not legal, coding, or payer-specific advice. Claim adjustment reason codes are maintained by X12 and are revised periodically; payer policy and your provider agreement govern in any specific case. Always read the remark codes transmitted with the denial — they frequently carry the detail this code does not.