Denial code

CO 31

The payer cannot find this patient as a member.

Fix and resubmit CO

What CO 31 means

CO — Contractual obligation — the provider absorbs it and cannot bill the patient.

So the balance cannot move to the patient. Either the appeal recovers it or the practice absorbs it. That makes the appeal decision the whole decision on this line.

Is it worth appealing?

Fix and resubmit. This is a correction, not an appeal. Appealing burns the deadline.

Why it fires

In the order we see it.

  1. A mistyped member ID, or a name that does not match the payer's record.

  2. The patient gave an old card and has since changed plans.

What to do

Re-verify the member ID, name spelling and date of birth against the card, then resubmit.

What actually wins it

The documentation, not the argument.

Current eligibility showing the correct member ID and plan.

The common mistake. Do not write this off as non-covered. It is almost always a data problem, and the claim pays once the identifiers match.

Where this comes from. This is our own reading of the code, not the payer's and not a copy of the standards text. We classify it from how these denials actually resolve. Where we are unsure, we say so rather than guessing.

Related codes

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