CO-252 denial code
An attachment is required to adjudicate this claim
How to fix it
Submit the required attachment through the payer's accepted channel and reference the claim number.
How to prevent it
Identify which services routinely require attachments for each payer and attach at submission.
In practice
A practice bills an unlisted procedure code for a device implantation with no specific code. The claim returns CO-252: an attachment is required to adjudicate this claim.
This was predictable. Unlisted codes carry no description a payer can price, so every payer requires an operative report and a comparison code with them. Submitting one without documentation guarantees this denial.
The fix is to resubmit through the payer's accepted attachment channel — electronic via the 275 transaction, portal upload, or fax with a claim-specific cover sheet — referencing the claim number so it is matched rather than filed as loose correspondence.
What sits behind it
CO-252 differs from CO-17 in an important way. CO-17 means the payer asked and did not receive. CO-252 means the documentation was required from the outset and never sent. One is a response failure; the other is a submission failure, and only the second is fully preventable at the front end.
The services that require attachments are a knowable list per payer: unlisted procedure codes, certain durable medical equipment, some drugs administered in office, procedures requiring a certificate of medical necessity, and anything billed with modifier 22 for increased procedural services. None of these are surprises.
The mechanical detail that decides whether this resolves is the attachment channel and the control number. An operative report faxed without a claim-specific cover sheet frequently never reaches the pending claim, and the practice records a second denial for documentation it did in fact send.
Related codes
Terms used here — Claim Scrubbing · Clean Claim · EDI 837
How we handle it — Claims Management · Denial Management · Medical Coding
Primary sources
The rules behind CO-252, at the bodies that publish them.
- Medicare Claims Processing Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — The operative manual for how Medicare claims must be coded, submitted, adjusted and appealed. When a payer policy and a vendor's advice disagree, this settles it.
- CMS-1500 claim form standards (opens in a new tab)
National Uniform Claim Committee — Maintainer of the CMS-1500 professional claim form and its data element definitions, plus the provider taxonomy code set.
- CPT code set (opens in a new tab)
American Medical Association — Maintainer of CPT. Annual changes to CPT are the most common cause of a sudden, unexplained rise in denials each January.
Every denial code with a guide
Authorization
Bundling
Contractual
Coverage
Data quality
Documentation
- CO-150Level of Service Not Supported
- CO-17Requested Records Not Received
- CO-252Attachment Required
Eligibility
Liability and workers comp
Patient responsibility
Provider eligibility
Timely filing
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-252
CO-252 means documentation was required from the outset and was not submitted. CO-17 means the payer asked for records and did not receive an adequate response. The first is a submission failure and is preventable at the front end; the second is a response failure.
Unlisted procedure codes, many durable medical equipment items, some office-administered drugs, anything needing a certificate of medical necessity, and claims billed with modifier 22. The list is knowable per payer and does not change often.
Through the payer's accepted channel — the electronic 275 transaction, portal upload, or fax with a claim-specific cover sheet — always referencing the claim number. An operative report sent without that reference frequently never reaches the pending claim.
Build a rule per payer identifying which codes require documentation, and hold those claims in scrubbing until the attachment is present. This denial is fully avoidable because the requirement is known before the claim is built.
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