Denial code CO-252: Attachment or documentation required
The payer needs supporting documentation it does not have before it will finish adjudicating the claim.
An attachment/other documentation is required to adjudicate this claim/service.
What CO-252 actually means
Adjudication is paused, not concluded. The payer wants records — an operative note, medical records, an invoice for an unlisted item, a certificate of medical necessity — and the remark codes name what. Because the claim is not truly denied, these resolve at a high rate when documentation is sent promptly; they turn into timely-filing losses when they sit in a queue nobody works.
Why this denial happens
- Records were requested to support medical necessity.
- An unlisted or miscellaneous procedure code requires a description and invoice.
- A certificate of medical necessity is required for DME.
- Accident or third-party liability details are required before adjudication.
How to resolve a CO-252 denial
- Read the remark codes to identify precisely which documentation is being requested.
- Submit the documentation through the payer’s preferred channel with the claim reference attached.
- Track the resubmission — documentation requests are frequently lost on the payer side and need follow-up.
How to prevent it
- Attach documentation up front for codes that predictably require it.
- Include a description and invoice with every unlisted procedure code at first submission.
Frequently asked
What does denial code CO-252 mean?
The payer needs supporting documentation it does not have before it will finish adjudicating the claim. The X12 description reads: "An attachment/other documentation is required to adjudicate this claim/service."
How do I fix a CO-252 denial?
Read the remark codes to identify precisely which documentation is being requested. Submit the documentation through the payer’s preferred channel with the claim reference attached. Track the resubmission — documentation requests are frequently lost on the payer side and need follow-up.
Can CO-252 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
Related billing terms
See how much CO-252 is costing you
Upload your 835 remittance files and PayerVista groups every denial by reason code, payer, and dollar impact — so this code stops being a claim you happened to notice and becomes a number you can work.
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.