CO-252CO group · Administrative

CO-252 denial code: an attachment or additional documentation is required

CO-252 isn't a no — it's a 'send more.' The faster you read the paired remark and submit exactly what it asks for, the faster it pays.

CO-252 means the payer cannot finish adjudicating until it receives additional documentation — typically medical records, an operative note, or an itemized bill. It is paired with a Remittance Advice Remark Code that names what is needed. It is highly resolvable: send the right documentation through the right channel, and the claim moves.

What CO-252 means

Some services require supporting records before payment — high-cost items, unlisted procedures, or claims flagged for review. CO-252 is the request for that documentation. The paired RARC specifies which records, and the response, not an argument, is what resolves it.

Why CO-252 fires

  • The service requires supporting medical records that weren't attached.
  • An unlisted or by-report procedure needs an operative note or description.
  • The payer flagged the claim for documentation review.
  • An itemized bill or invoice is required for the charge.

Is CO-252 worth appealing?

Sometimes worth appealing

Treat it first as a documentation request, not an appeal: read the paired remark, gather exactly what it names, and submit through the payer's records channel. It becomes a formal appeal if the payer denies after you have provided complete, responsive documentation — at which point you appeal with proof of what was sent and when.

How to resolve or appeal CO-252

  1. 1

    Read the paired remark

    The RARC names the specific documentation required — records, operative note, itemized bill. That is your checklist.

  2. 2

    Submit through the right channel

    Send the documentation the way the payer specifies (portal, fax, or attachment), referencing the claim so it's matched, not lost.

  3. 3

    Appeal only after a complete response

    If the claim is denied despite complete, responsive documentation, appeal with proof of what was submitted and when.

CO-252 — frequently asked

Is CO-252 a denial?
It's a development request more than a final denial — the payer needs documentation to adjudicate. Supplying the right records usually resolves it without a formal appeal.
What documentation does CO-252 want?
Whatever the paired remark code specifies — commonly medical records, an operative or procedure note, or an itemized bill. Send exactly that, referenced to the claim.

Related guides

CO-16 · AdministrativeCO-50 · Medical necessityCO-197 · Authorization

Sources

Reason-code meanings are paraphrased from the X12 Claim Adjustment Reason Code list for plain-language reference; they are not reproduced verbatim. This is general information, not legal, coding, or medical advice — always confirm against the payer's remittance and policy.

Turn this CO-252 denial into a signed appeal

Upload the denied EOB and Merits builds a complete CO-252 appeal — the argument, the payer's own coverage criteria, and your federal appeal rights, every claim cited to a named source. $9 a letter. No account.

Appeal a denial →