CO-252 Denial Code: Supporting documentation needed to process the claim
The payer cannot finish processing the claim until you send supporting documentation. A remark code on the same remittance line should identify what is needed.
- Group code
- CO - Contractual Obligation
- Code type
- CARC
- Billable to patient?
- No - claim is pended for documentation; not patient responsibility
- Appealable?
- Send the records - no appeal needed
- Category
- Missing or Invalid Information
- Common pairing
- N479
CAS*CO*252*125.00On a paper EOB it shows as CO-252.What CO-252 means
CO-252 is a documentation request, not a final judgment on the claim: the payer has it but will not adjudicate until it receives an attachment - medical records, an operative note, an invoice, a primary payer's EOB, or similar. X12 requires this code to travel with at least one remark code, so check the RARC on the same line to see exactly what is missing (for example, N479 for a primary EOB). Because it lands in the CO group, nothing here shifts to the patient. The claim typically sits pended until you respond, and most payers give a fixed window before they finalize the denial, so speed matters.
Common causes
- Services that routinely trigger records requests - high-dollar claims, unlisted codes, or modifier 22 - were billed without proactive attachments.
- A required attachment such as an invoice, operative report, or primary EOB was not sent with the initial claim.
- The payer's medical policy requires notes for that procedure code and the claim went out without them.
- Documentation was sent but never linked to the claim - wrong attachment control number, or faxed without the claim reference.
- The payer is auditing a billing pattern and pending claims for records review.
How to fix it
- Read the paired remark code first - it usually names the specific document the payer wants.
- If the remittance does not say, call the payer or check the portal to confirm exactly what to send and where.
- Submit the records through the payer's documented channel with the claim number and attachment control number clearly referenced.
- Track the response deadline and calendar a follow-up to confirm the claim moved out of pended status.
- If you already sent the documentation, resubmit it with proof of the original submission and request reprocessing.
How to prevent it
- Keep a payer-specific list of codes that always draw records requests and attach documentation with the initial claim (PWK segment or portal upload).
- Use unlisted codes only with a complete description and supporting documentation included up front.
- Work 252s within days, not weeks - documentation windows are short, and a missed window converts a pend into a final denial.